CHANGELOG.md

@@ -4,6 +4,25 @@ All notable changes to FastSync are documented here. Versions match
 `PROTOCOL_VERSION` (printed by `fastsync --version`); the client and server must
 run the same version because the handshake is strict.
 
+## [Unreleased]
+
+### Security
+
+- Enforce the daemon's per-module `max connections` cap and add a global
+  `max connections per host` cap plus a cross-process `auth lockout`
+  (`auth lockout threshold` / `auth lockout duration`). Because the listener
+  forks one child per connection, the counters live in an anonymous shared
+  mapping created before the accept loop and reclaimed by the parent's
+  `SIGCHLD` handler, so the per-module, per-source and auth-failure state is
+  shared across every child (including after `SIGKILL`). The per-source table
+  now has a bounded lifetime (expired-lockout/idle entries are reclaimed, with a
+  rate-limited warning when it is genuinely full), and the occupancy counters are
+  re-derived from the shared slot table on every child exit so a child killed
+  mid-registration cannot leak a count. Trusted loopback peers are exempt from the
+  per-host cap and the auth lockout (they share one address); clients behind a
+  shared NAT/proxy still share a single per-host budget and lockout, which is
+  documented.
+
 ## [2.20.0] - 2026-09-13
 
 ### Security

CMakeLists.txt

@@ -86,6 +86,7 @@ set(SHARED_SRCS
 	src/shared/config.c
 	src/shared/credentials.c
 	src/shared/daemon_conf.c
+	src/shared/daemon_limits.c
 	src/shared/data.c
 	src/shared/delay_updates.c
 	src/shared/delta.c
@@ -205,6 +206,7 @@ set(TEST_SRCS
 	tests/test_config.c
 	tests/test_credentials.c
 	tests/test_daemon_conf.c
+	tests/test_daemon_limits.c
 	tests/test_data.c
 	tests/test_delay_updates.c
 	tests/test_delta.c

README.md

@@ -508,18 +508,47 @@ defaults to the current directory. |
 implicit global section, then `[module]` sections). Besides `port`, `motd file`,
 and `address`, the global section accepts:
 
-- `max connections = N` — cap on concurrent connections, default 100. The
+- `max connections = N` — global cap on concurrent connections, default 100. The
   listener enforces it; `0`, negative, and non-numeric values are parse errors.
+- `max connections per host = N` — cap on concurrent connections from a single
+  source IP, default 0 (unlimited). Enforced across all forked connection
+  children through a shared registry.
 - `auth failure delay = MS` — milliseconds to sleep after a failed
-  authentication, default 500. `0` disables it and the value is capped at 60000,
+  authentication, default 500. `0` disables it and the value is capped at 5000,
   so online password guessing is rate-limited per connection. Successful auths
   are never delayed.
+- `auth lockout threshold = N` — number of failed authentications from one source
+  IP before that source is locked out, default 10; `0` disables the lockout. The
+  failure counter is shared across every connection child, so the lockout holds
+  even when the next attempt is handled by a different forked child.
+- `auth lockout duration = SECONDS` — how long a locked-out source is refused
+  (default 300). A locked-out client is refused before any SCRAM challenge is
+  sent; a successful authentication clears the counter.
 - `hosts allow` / `hosts deny` — comma- and/or whitespace-separated host access
   patterns.
 
-A `[module]` may also set `max connections` (parsed and validated but not
+A `[module]` may also set `max connections` (0 = unlimited; enforced per module
-enforced per module — the global cap applies to the whole listener) and its own
+across all connection children) and its own `hosts allow`/`hosts deny`.
-`hosts allow`/`hosts deny`.
+
+The per-host cap and the shared auth lockout identify a source by its numeric
+peer IP. **Loopback peers (127.0.0.0/8, IPv6 `::1`) are exempt**: every local
+client shares that one address, so counting or locking them out would let one
+local process deny service to all the others. The per-module and global
+`max connections` caps still apply to loopback. Because the key is the peer IP,
+`max connections per host` and `auth lockout` also cannot distinguish clients
+behind the same NAT, proxy, or reverse-proxy address — they share one budget and
+one lockout counter, so an over-aggressive lockout can affect unrelated users
+behind that address. Prefer TLS client certificates (`--client-cn`) plus
+`hosts allow`/`hosts deny` for per-client policy when clients share an address,
+and size `auth lockout threshold` accordingly.
+
+The shared per-source table has a bounded lifetime: an entry with no live
+connection is reclaimed once its lockout has expired, or after it has been idle
+(300 s). If every entry is still live or locked, a new source is admitted without
+per-host accounting (fail open) and a rate-limited warning is logged; the
+per-module cap and host ACLs still apply. The occupancy counters are re-derived
+from the shared slot table after every child exit, so a child killed mid-transfer
+(or mid-registration) cannot leak a slot or an occupancy count.
 
 Host patterns are `*` (match all), IPv4/IPv6 literals, or IPv4/IPv6 CIDR
 (`10.0.0.0/8`, `2001:db8::/32`). Hostnames are not resolved, so hostname globs

RSYNC_COMPAT.md

@@ -627,7 +627,7 @@ now transmits targets (the prior behavior was broken/partial); its status moved
 |------|-------------------|-----------------|-------|
 | `--daemon` | Run as rsync daemon | ✅ Implemented | Wave A: a real persistent listener. `fastsync-server --daemon --config FILE` (plus `--no-detach` to stay foreground; without it the listener detaches to the background after binding) reads a FastSync-native module config file and serves each connection confined to the requested module's `path` root (never a client-chosen root; every client-chosen-ownership/super-user request (`--numeric-ids`/`--chown`/`--usermap`/`--groupmap`/`--fake-super`/`--copy-as`/explicit `--super`) is refused unless the module opts in with `client owner = yes`, and the operator `--no-super` veto is honored). TCP/TLS via the existing `--tls` stack; plaintext still requires `--allow-unauthenticated` (same secure default as the standalone server). Client destinations use rsync's `host::module/path` form. Wire/protocol: the config frame gained a trailing daemon-module string and `PROTOCOL_VERSION` was bumped **2.14.0 → 2.15.0** (see the Daemon Mode notes below). Daemon mode is built in FastSync's own protocol/config grammar, not rsync's SMB/daemon option encoding |
 | `--config=FILE` | Alternate rsyncd.conf file | ✅ Implemented | Wave A: selects the daemon config file. Default when omitted (in `--daemon` mode): `~/.config/fastsync/fastsyncd.conf` if it exists, else `/etc/fastsyncd.conf`. The grammar is FastSync-native (documented in the Daemon Mode notes below) and strictly rejects unknown keys so a typo can never silently change what a module serves; requires `--daemon` |
-| `--dparam=OVERRIDE` | Override global daemon config | ✅ Implemented | Wave A: overrides one global scalar from the command line (`--dparam port=8734` and `--dparam=KEY=VALUE` both work). Limited to the global keys the grammar defines (`port`, `motd file`, `address`, `max connections`, `auth failure delay`, `hosts allow`, `hosts deny`); keys are case-insensitive and unknown keys/invalid values are rejected. Requires `--daemon` |
+| `--dparam=OVERRIDE` | Override global daemon config | ✅ Implemented | Wave A: overrides one global scalar from the command line (`--dparam port=8734` and `--dparam=KEY=VALUE` both work). Limited to the global keys the grammar defines (`port`, `motd file`, `address`, `max connections`, `max connections per host`, `auth failure delay`, `auth lockout threshold`, `auth lockout duration`, `hosts allow`, `hosts deny`); keys are case-insensitive and unknown keys/invalid values are rejected. Requires `--daemon` |
 | `--no-detach` | Don't detach from parent | ✅ Implemented | Wave A: with `--daemon`, keeps the listener in the foreground (what integration tests use). Without it the daemonizes (fork/setsid, stdio redirected to /dev/null) after the listening socket is bound. Requires `--daemon` |
 | `--password-file=FILE` | Read daemon password from file | ✅ Implemented | A7 daemon auth. Client: `--password-file` supplies `user:password` for a `host::module/path` destination (the username is taken from this file, so `user@host::module` stays rejected); the literal password is held client-side only for the SCRAM handshake and wiped at teardown. Server (`fastsync-server --daemon --password-file FILE`): the salted-PBKDF2 verifier store that modules with `auth users` are verified against. **Neither the password nor any replayable bearer value crosses the wire or is stored server-side** — the store holds a per-user salt plus derived keys, and the daemon proves the secret with a per-connection nonce challenge. The file must be private to its owner: both the client and server verify the exact inode they read (open-then-`fstat`, so the check cannot be raced) and refuse a `--password-file`/`--early-input` that is not owned by the current user or grants any group/other permission bit (mode 0600), mirroring the TLS private-key check. A process-substitution pipe (`--early-input <(vault ...)`) is still accepted when it satisfies those checks. See the Daemon Mode notes below for the file formats and the plaintext/TLS caveat |
 | `--early-input=FILE` | Use FILE for daemon early exec | ✅ Implemented | Server-only (requires `--daemon`): a second credential-store file, same new-format grammar as `--password-file`, read before the listener accepts connections (a secrets-manager / process-substitution source). Its entries layer over `--password-file`: byte-identical verifiers dedupe, a conflicting verifier for the same user is a startup error. A daemon whose modules declare `auth users` must be given at least one of the two, or it refuses to start (fail closed) |
@@ -635,9 +635,9 @@ now transmits targets (the prior behavior was broken/partial); its status moved
 
 **Daemon Mode notes (Wave A protocol 2.15.0; A7 auth protocol 2.19.0; MOTD no bump):** FastSync daemon mode is supported in FastSync's own protocol/config grammar, not rsync's SMB/daemon option encoding.
 
-- **Config grammar** (`fastsyncd.conf`): line-based; an implicit global section first, then `[module]` sections. Keys are case-insensitive, values are trimmed and may be wrapped in one layer of double quotes (`path = "/srv/my dir"`). `#` and `;` at the start of a line (after leading whitespace) are full-line comments; inline comments and `\` continuations are not supported. Lines are bounded (4096 chars). Global keys: `port` (default 873), `motd file` (the daemon sends its bounded, escaped content to a client after the module gate/auth accepts, unless the client passes `--no-motd`), `address` (optional bind address), `max connections` (positive integer cap on concurrent connections, default 100; 0/negative/garbage is a parse error), `auth failure delay` (milliseconds to sleep after a failed authentication, default 500; 0 disables, capped at 5000), `hosts allow` and `hosts deny` (comma- and/or whitespace-separated host access patterns — see the host access control note below). Module keys: `path` (required; the daemon-side authorized root for that module), `read only` (yes/no/true/false/1/0, default no), `client owner` (yes/no/true/false/1/0, default no; opts the module into client-chosen ownership — see below), `auth users` (comma list), `max connections` (optional per-module cap; parsed and stored but **not enforced** — the global cap applies to the whole listener), `hosts allow`/`hosts deny` (per-module host access lists). **Unknown keys and malformed lines are parse-and-reject errors** (never silently ignored), so a typo cannot change what a module serves.
+- **Config grammar** (`fastsyncd.conf`): line-based; an implicit global section first, then `[module]` sections. Keys are case-insensitive, values are trimmed and may be wrapped in one layer of double quotes (`path = "/srv/my dir"`). `#` and `;` at the start of a line (after leading whitespace) are full-line comments; inline comments and `\` continuations are not supported. Lines are bounded (4096 chars), and at most 256 `[module]` sections are accepted. Global keys: `port` (default 873), `motd file` (the daemon sends its bounded, escaped content to a client after the module gate/auth accepts, unless the client passes `--no-motd`), `address` (optional bind address), `max connections` (positive integer cap on concurrent connections, default 100; 0/negative/garbage is a parse error), `max connections per host` (concurrent-connection cap per source IP, default 0 = unlimited), `auth failure delay` (milliseconds to sleep after a failed authentication, default 500; 0 disables, capped at 5000), `auth lockout threshold` (failed authentications from one source before lockout, default 10; 0 disables), `auth lockout duration` (seconds a locked-out source is refused, default 300), `hosts allow` and `hosts deny` (comma- and/or whitespace-separated host access patterns — see the host access control note below). Module keys: `path` (required; the daemon-side authorized root for that module), `read only` (yes/no/true/false/1/0, default no), `client owner` (yes/no/true/false/1/0, default no; opts the module into client-chosen ownership — see below), `auth users` (comma list), `max connections` (optional per-module cap, 0 = unlimited; enforced across all connection children), `hosts allow`/`hosts deny` (per-module host access lists). **Unknown keys and malformed lines are parse-and-reject errors** (never silently ignored), so a typo cannot change what a module serves.
 - **Host access control (`hosts allow`/`hosts deny`):** both keys accept a comma- and/or whitespace-separated list of patterns and may appear globally and/or per module (multiple config-file lines append; a `--dparam` override replaces). Supported patterns are `*` (match all), an IPv4 or IPv6 literal (`10.0.0.1`, `2001:db8::1`), and an IPv4/IPv6 CIDR (`10.0.0.0/8`, `2001:db8::/32`). Hostname patterns are **not** supported: because the peer is always a numeric address and no reverse DNS is performed, a hostname/glob pattern would silently never match, so it is rejected at load time (fail-closed) instead of being accepted as a dead rule. An IPv4 peer on a dual-stack IPv6 listener is normalized from its `::ffff:a.b.c.d` form so IPv4 patterns match it. rsync-like semantics: a matching `hosts deny` rejects; if any `hosts allow` entries exist, a peer matching none of them is rejected; deny takes precedence over allow. The daemon enforces the global list first, then the selected module's list, **before authentication** in `server_module_gate`, with an audit log line naming the peer, the module and the outcome. The numeric peer address is obtained with `getpeername`+`inet_ntop` (`utils_fd_peer_ip`, handling both address families); when it cannot be obtained a module with any ACL fails closed (refused), while an ACL-free module continues and logs at debug. A malformed pattern (e.g. an out-of-range CIDR prefix) is a parse error at load time.
-- **Connection cap and auth throttle:** the global `max connections` key (default 100) is plumbed into the listener (`transport_tcp.c`), which rejects a connection once the accept-loop parent's active-child count reaches it; the IPv4/IPv6 peer is logged for every accepted connection. The optional per-module `max connections` key is parsed and validated but **not enforced** (connections are counted in the parent before the client's module is known); the daemon logs a startup warning for any module that sets it. On a failed authentication the per-connection child sleeps the global `auth failure delay` (default 500 ms, 0 disables, capped at 5000) via `nanosleep` before the connection closes, rate-limiting online guessing without delaying a success.
+- **Connection caps, shared registry and auth lockout:** the global `max connections` key (default 100) is plumbed into the listener (`transport_tcp.c`), which rejects a connection once the accept-loop parent's active-child count reaches it; the IPv4/IPv6 peer is logged for every accepted connection. Because the listener forks one child per connection, the per-module `max connections` cap, the global `max connections per host` cap, and the auth-failure counter live in a fixed-size registry carved from an anonymous shared mapping (`daemon_limits.c`, `mmap(MAP_SHARED|MAP_ANONYMOUS)`) created by the parent before the accept loop, so every forked child shares the same counters (C11 atomics only — never a pthread lock, which can deadlock in a forked child). The parent reserves a registry slot per accepted connection and the child records the selected module and source IP once known; the parent's `SIGCHLD` handler reclaims the slot when the child dies (including `SIGKILL`) and re-derives the per-module and per-source occupancy counts from the surviving REGISTERED slots, so a child killed mid-registration cannot leak a count. The per-source table has a bounded lifetime: an entry with no live connection is reclaimed after its lockout expires or it has been idle (300 s); if the table is genuinely full the per-source cap/lockout fails open for new sources (per-module cap and ACLs still apply) with a rate-limited warning. The per-module cap (0 = unlimited) is enforced after the module lookup and before auth; per-source identity reuses the normalized numeric peer address (`utils_fd_peer_ip`, IPv4-mapped IPv6 collapsed to IPv4), and a trusted loopback peer (127.0.0.0/8 / `::1`, `utils_fd_peer_is_local`) is exempt from the per-source cap and the auth lockout because all local clients share one address (the per-module/global caps still apply). Clients behind a shared NAT/proxy address likewise share one per-source budget and lockout counter. A failed authentication increments the shared per-source failure count and, once `auth lockout threshold` (default 10; 0 disables) is reached, the source is refused for `auth lockout duration` seconds (default 300) before any challenge is sent, even when the next attempt is handled by a different forked child; a successful authentication clears the counter. On a failed authentication the per-connection child still sleeps the global `auth failure delay` (default 500 ms, 0 disables, capped at 5000) via `nanosleep`, rate-limiting online guessing without delaying a success. A missing registry (allocation failure) degrades to the global cap and host ACLs rather than refusing to start.
 - **Module selection & confinement:** the client requests a module with an rsync-style `host::module[/path]` destination. The module name crosses the wire as a trailing string on the config frame (bumping `PROTOCOL_VERSION` 2.14.0 → 2.15.0; the bump is required because the config-frame layout changed and the strict same-version handshake is what prevents a peer from desynchronizing on the new trailing field). The daemon looks the module up in ITS OWN config and uses the module's `path` as the authorized root through the exact same `configure_authorization` confinement the standalone server applies to `--destination-root` (`file_open_secure_parent`, `has_path_traversal`, `path_is_within`); the client never supplies the root, every client-chosen-ownership/super-user request is refused unless the module declares `client owner = yes` (the daemon's per-module opt-in, see below), and the operator `--no-super` veto forces super-user activities off for every daemon connection. The client's `/path` part is relative inside the module and is rejected if absolute or if it contains `..`. Unknown modules are refused before any data moves (the run fails cleanly at the config handshake). An absolute destination and a module request against a non-daemon server are also refused.
 - **`client owner` (client-chosen-ownership opt-in):** by default a daemon module refuses every request that would let the client pick an owner or ask for super-user activities — `--numeric-ids`, `--chown`, `--usermap`/`--groupmap`, `--fake-super`, `--copy-as`, and an explicit `--super` — at the config handshake (before `STATUS_OK`), because a daemon has no per-module opt-in for client-chosen ownership and any anonymous client could otherwise force arbitrary owner ids inside the module root. `client owner = yes` opts a single module in, allowing those requests within that module's root (the standalone listener and the SSH `--stdio` server always honor them for their single operator-authorized root). Without the opt-in the daemon also forces super-user **device** activity off for that connection — char/block device-node creation (`--devices`) and `--write-devices` — even under the default `AUTO` mode, so a non-opted module can never be made to `mknod` or write a raw device; those entries are skipped (not refused) so an ordinary `-a` push still succeeds without device nodes. The opt-in does **not** lift the privilege requirement: `--copy-as` still needs a root receiver, and the operator `--no-super` veto still forces super-user activities off for every connection. The daemon logs a prominent startup warning for each `client owner = yes` module so the operator's deliberate choice is visible.
 - **`read only` safe default:** every network transfer FastSync currently supports is a push that writes under the module root, so a `read only` module refuses the connection (clear server log "module is read only"; the client exits non-zero, nothing is transferred). A future pull/list operation can be opened up when it exists; the knob is already stored.

src/client/client_cli.c

@@ -608,7 +608,15 @@ typedef struct {
   size_t offset; /* offsetof of the boolean target field in Config */
 } NegatableOption;
 
-/* Options that map directly onto a Config field with no side effects. */
+/* Options that map directly onto a Config field with no side effects.
+ *
+ * NOTE: these CLI tables are intentionally NOT generated from the wire-field
+ * X-macro table in config.h.  The two sets only overlap partially: the CLI
+ * surface also carries client-only fields that never cross the wire (rsh,
+ * outbuf, remote-option, batch paths, trust-sender, ...) and needs flag/alias/
+ * negation semantics that the wire table does not model.  Keeping them
+ * hand-maintained is deliberate; the shared contract is enforced at the wire
+ * boundary by config.[ch] and the golden test. */
 static const OptionEntry OPTION_TABLE[] = {
     {"--dry-run", "-n", OPT_FLAG, offsetof(Config, dry_run)},
     {"--remove-source-files", NULL, OPT_FLAG, offsetof(Config, remove_source_files)},

src/client/client_send.c

@@ -1157,6 +1157,7 @@ static int send_append(const Client* client, File* file, Config* config,
     tail_view.data = (char*)file->data->data + off;
     tail_view.size = tail_len;
     tail_view.protocol_charge = 0;
+    tail_view.owner = NULL;
     ok = send_data(fd, &tail_view);
   }
   return ok ? 0 : -1;

src/server/server.c

@@ -2,6 +2,7 @@
 #include "charset.h"
 #include "credentials.h"
 #include "daemon_conf.h"
+#include "daemon_limits.h"
 #include "delay_updates.h"
 #include "file.h"
 #include "identity.h"
@@ -29,8 +30,6 @@
 #include <time.h>
 #include <openssl/x509.h>
 
-static char* authorized_root;
-static int authorized_root_fd = -1;
 static bool allow_delete;
 static bool trust_sender;
 static bool allow_unauthenticated;
@@ -56,6 +55,12 @@ static DaemonConf* g_daemon_conf = NULL;
  * such a module exists. */
 static CredentialStore* g_credentials = NULL;
 
+/* Cross-process connection registry (per-module and per-source caps plus the
+ * shared auth lockout), created once in main BEFORE the accept loop forks and
+ * shared read-only-by-pointer with every connection child.  NULL outside daemon
+ * mode or when the mapping could not be allocated (global cap + ACLs remain). */
+static DaemonLimitRegistry* g_daemon_limits = NULL;
+
 /* Opaque context threaded through to the config-frame gate: the connection's
  * SSL object (NULL over plaintext) so the gate can warn when a credential
  * exchange is not encrypted, plus the super-mode override the gate decides on.
@@ -75,6 +80,13 @@ typedef struct ModuleGateContext {
    * not classify the peer; an ACL-configured module then fails closed. */
   bool has_peer_ip;
   char peer_ip[INET6_ADDRSTRLEN];
+  /* True when the peer is provably loopback (utils_fd_peer_is_local, fail
+   * closed).  A trusted local/SSH peer is exempt from the per-host cap and the
+   * cross-process auth lockout: every loopback client shares the 127.0.0.1
+   * identity, so counting/locking them out would let one local client deny
+   * service to (or leak lockout state about) all the others.  The per-module and
+   * global caps still apply. */
+  bool is_local;
 } ModuleGateContext;
 
 /* Server half of the SCRAM challenge/response (A7 remediation, protocol
@@ -187,13 +199,10 @@ static bool tls_client_identity_allowed(SSL* ssl) {
 }
 
 static void release_authorization(void) {
-  file_set_authorized_root(-1, NULL);
+  int root_fd = utils_get_authorized_root_fd();
-  utils_set_authorized_root_fd(-1);
+  utils_set_authorized_root(-1, NULL);
-  if (authorized_root_fd >= 0)
+  if (root_fd >= 0)
-    close(authorized_root_fd);
+    close(root_fd);
-  authorized_root_fd = -1;
-  free(authorized_root);
-  authorized_root = NULL;
 }
 
 static bool path_is_within(const char* root, const char* path) {
@@ -219,13 +228,11 @@ static bool ensure_receive_root(const Config* config) {
 static bool configure_authorization(const char* root) {
   char resolved[PATH_MAX];
   if (!root) {
-    file_set_authorized_root(-1, NULL);
     utils_set_authorized_root(-1, NULL);
     return false;
   }
   int root_fd = open(root, O_RDONLY | O_DIRECTORY | O_NOFOLLOW | O_CLOEXEC);
   if (root_fd < 0) {
-    file_set_authorized_root(-1, NULL);
     utils_set_authorized_root(-1, NULL);
     return false;
   }
@@ -234,26 +241,12 @@ static bool configure_authorization(const char* root) {
   if (fd_path_length < 0 || (size_t)fd_path_length >= sizeof(fd_path) ||
       !realpath(fd_path, resolved)) {
     close(root_fd);
-    file_set_authorized_root(-1, NULL);
     utils_set_authorized_root(-1, NULL);
     return false;
   }
-  authorized_root = str_dup(resolved);
+  if (!utils_set_authorized_root(root_fd, resolved)) {
-  if (!authorized_root) {
+    /* The setter already cleared the fd/path state on allocation failure. */
     close(root_fd);
-    file_set_authorized_root(-1, NULL);
-    utils_set_authorized_root(-1, NULL);
-    return false;
-  }
-  authorized_root_fd = root_fd;
-  if (!file_set_authorized_root(authorized_root_fd, authorized_root) ||
-      !utils_set_authorized_root(authorized_root_fd, authorized_root)) {
-    file_set_authorized_root(-1, NULL);
-    utils_set_authorized_root(-1, NULL);
-    close(authorized_root_fd);
-    authorized_root_fd = -1;
-    free(authorized_root);
-    authorized_root = NULL;
     return false;
   }
   return true;
@@ -292,6 +285,60 @@ static const DaemonModule* module_gate_lookup_module(const Config* config, const
   return module;
 }
 
+/* Index of `module` within the loaded config's module array (the registry's
+ * per-module counter key).  Returns -1 when it cannot be resolved. */
+static int daemon_module_index(const DaemonModule* module) {
+  if (!g_daemon_conf || !module || module < g_daemon_conf->modules ||
+      module >= g_daemon_conf->modules + g_daemon_conf->module_count)
+    return -1;
+  return (int)(module - g_daemon_conf->modules);
+}
+
+/* Shared-registry admission: reserve this connection's slot for the selected
+ * module and the peer source IP.  Enforces the per-module `max connections` and
+ * the global `max connections per host` across every forked child.  Runs before
+ * auth/ownership so a client that is over a cap is refused before any work.
+ * The per-source cap is skipped when the peer cannot be classified (host ACLs
+ * fail closed separately); the module cap still applies.  A missing registry
+ * (allocation failure / non-fork path) fails open -- the global cap and ACLs
+ * still bound the listener. */
+static const char* module_gate_check_limits(const Config* config, const DaemonModule* module,
+                                            ModuleGateContext* gate_ctx) {
+  if (!g_daemon_limits)
+    return NULL;
+  int slot = transport_tcp_current_slot();
+  if (slot < 0)
+    return NULL; /* not on the forked accept-loop path (e.g. --stdio) */
+  int module_index = daemon_module_index(module);
+  if (module_index < 0)
+    return NULL;
+  /* A trusted loopback peer is exempt from the per-source cap: pass an
+   * unparseable peer so the registry skips per-source tracking, while the
+   * per-module cap below is still enforced.  Remote peers are tracked normally. */
+  const char* peer =
+      (!gate_ctx || gate_ctx->is_local || !gate_ctx->has_peer_ip) ? "" : gate_ctx->peer_ip;
+  DaemonLimitResult result =
+      daemon_limits_register(g_daemon_limits, slot, module_index, peer, module->max_connections);
+  switch (result) {
+  case DAEMON_LIMIT_OK:
+    return NULL;
+  case DAEMON_LIMIT_MODULE_FULL:
+    log_message(LOG_LEVEL_ERROR,
+                "daemon module '%s': 'max connections' cap (%d) reached; refusing %s",
+                config->module, module->max_connections, peer[0] ? peer : "peer");
+    return "requested daemon module is at its connection limit";
+  case DAEMON_LIMIT_HOST_FULL:
+    log_message(LOG_LEVEL_ERROR,
+                "daemon: 'max connections per host' cap (%d) reached for %s; refusing module '%s'",
+                g_daemon_conf->global.max_connections_per_host, peer[0] ? peer : "peer",
+                config->module);
+    return "too many concurrent connections from this host";
+  case DAEMON_LIMIT_UNAVAILABLE:
+  default:
+    return NULL;
+  }
+}
+
 /* Per-module client-chosen ownership / super-user policy (P7 Wave E hardening):
  * a daemon module refuses EVERY ownership-affecting request (--numeric-ids,
  * --chown, --usermap/--groupmap, --fake-super, --copy-as, explicit --super)
@@ -396,6 +443,22 @@ static ModuleAuthResult module_gate_authenticate(const Config* config, const Dae
                                                  ModuleGateContext* gate_ctx, const char** error) {
   if (module->auth_user_count == 0)
     return MODULE_AUTH_ACCEPTED;
+  /* Cross-process lockout: a source that failed too many authentications is
+   * refused before the challenge is sent (the counter lives in the shared
+   * registry, so it spans every forked child and survives a child exit).  A
+   * trusted loopback peer is exempt: all local clients share the 127.0.0.1
+   * identity, so a lockout would let one deny the others. */
+  if (g_daemon_limits && gate_ctx && gate_ctx->has_peer_ip && !gate_ctx->is_local) {
+    int remaining = 0;
+    if (daemon_limits_auth_locked(g_daemon_limits, gate_ctx->peer_ip, &remaining)) {
+      log_message(LOG_LEVEL_ERROR,
+                  "daemon module '%s': source %s is locked out after repeated authentication "
+                  "failures (%d s remaining); refusing",
+                  config->module, gate_ctx->peer_ip, remaining);
+      *error = "too many failed authentication attempts from this host; try again later";
+      return MODULE_AUTH_REFUSED;
+    }
+  }
   /* Fail closed: no store -> refuse (server misconfiguration, STATUS_ERROR). */
   if (g_credentials == NULL) {
     log_message(LOG_LEVEL_ERROR,
@@ -450,10 +513,17 @@ static ModuleAuthResult module_gate_authenticate(const Config* config, const Dae
                 "daemon module '%s': authentication failed for user '%s' from %s; refusing",
                 config->module, escaped_user ? escaped_user : "(none)", peer);
     free(escaped_user);
-    /* Rate-limit online guessing per connection (no delay on success). */
+    /* Count the failure in the shared registry (locks the source out once the
+     * configured threshold is reached) and rate-limit online guessing per
+     * connection (no delay on success).  A loopback peer is exempt from the
+     * shared counter. */
+    if (g_daemon_limits && gate_ctx->has_peer_ip && !gate_ctx->is_local)
+      daemon_limits_auth_record_failure(g_daemon_limits, gate_ctx->peer_ip);
     daemon_auth_failure_delay();
     return MODULE_AUTH_TERMINATED;
   }
+  if (g_daemon_limits && gate_ctx->has_peer_ip && !gate_ctx->is_local)
+    daemon_limits_auth_record_success(g_daemon_limits, gate_ctx->peer_ip);
   char* escaped_user = output_escape(config->auth_user, config->eight_bit_output);
   log_message(LOG_LEVEL_INFO, "daemon module '%s': user '%s' from %s authenticated", config->module,
               escaped_user ? escaped_user : "<allocation failed>",
@@ -559,8 +629,14 @@ static const char* server_module_gate(const Config* config, void* context) {
         utils_fd_peer_ip(gate_ctx->fd, gate_ctx->peer_ip, sizeof(gate_ctx->peer_ip));
     if (!gate_ctx->has_peer_ip)
       log_message(LOG_LEVEL_DEBUG, "daemon module '%s': peer address unavailable", config->module);
+    /* utils_fd_peer_is_local is fail-closed (getpeername must succeed and report
+     * a loopback peer), so "cannot tell" is never treated as trusted. */
+    gate_ctx->is_local = utils_fd_peer_is_local(gate_ctx->fd);
   }
   error = module_gate_check_hosts(config, module, gate_ctx);
+  if (error)
+    return error;
+  error = module_gate_check_limits(config, module, gate_ctx);
   if (error)
     return error;
   error = module_gate_check_ownership(config, module, gate_ctx);
@@ -590,6 +666,7 @@ void handler(int file_descriptor) {
   gate_ctx.super_mode_override = -1;
   gate_ctx.has_peer_ip = false;
   gate_ctx.peer_ip[0] = '\0';
+  gate_ctx.is_local = false;
   /* All teardown state starts empty so the single `done` epilogue is safe to
    * reach from any error path (including before the config frame arrives). */
   Config* config = NULL;
@@ -615,6 +692,7 @@ void handler(int file_descriptor) {
    * in effect.  A client's --timeout tightens only that client's own protocol
    * I/O and the server's socket read/write timeout is the transport default. */
   protocol_session_set_io_timeout(&session, config->timeout);
+  const char* authorized_root = utils_get_authorized_root_path();
   if (!authorized_root) {
     log_message(LOG_LEVEL_ERROR, "No server-side destination root configured");
     goto done;
@@ -880,7 +958,9 @@ static void print_server_usage(void) {
   printf("                      fastsyncd.conf, else /etc/fastsyncd.conf)\n");
   printf("  --dparam=KEY=VALUE  Override one global config key on the command line\n");
   printf("                      (port, motd file, address, max connections,\n");
-  printf("                      auth failure delay, hosts allow, hosts deny)\n");
+  printf("                      max connections per host, auth failure delay,\n");
+  printf("                      auth lockout threshold, auth lockout duration,\n");
+  printf("                      hosts allow, hosts deny)\n");
   printf("  --no-detach         Stay in the foreground (default detaches to\n");
   printf("                      background when running --daemon)\n");
   printf("  --password-file=FILE  Credential store for modules that declare\n");
@@ -1096,11 +1176,10 @@ int main(int argc, char* argv[]) {
                     "unless the module is intentionally open to the network",
                     g_daemon_conf->modules[i].name);
       if (g_daemon_conf->modules[i].max_connections > 0)
-        log_message(LOG_LEVEL_WARNING,
+        log_message(LOG_LEVEL_INFO,
-                    "daemon module '%s': per-module 'max connections' is stored but not enforced "
+                    "daemon module '%s': per-module 'max connections' cap = %d (enforced "
-                    "per module; the global 'max connections' cap (%d) applies to the whole "
+                    "across all connection children)",
-                    "listener",
+                    g_daemon_conf->modules[i].name, g_daemon_conf->modules[i].max_connections);
-                    g_daemon_conf->modules[i].name, g_daemon_conf->global.max_connections);
     }
     /* Daemon credential store (Wave B).  --password-file and --early-input
      * feed the same store, loaded BEFORE the listener forks so every
@@ -1144,6 +1223,21 @@ int main(int argc, char* argv[]) {
                       module->name, module->auth_users[j]);
       }
     }
+    /* Shared cross-process registry for the per-module / per-source caps and
+     * the auth lockout.  Created HERE in the parent before any accept-loop
+     * fork; every connection child inherits the mapping.  A failure degrades to
+     * "registry disabled" (the global cap and host ACLs still apply) rather
+     * than refusing to start. */
+    g_daemon_limits = daemon_limits_create((int)g_daemon_conf->global.max_connections,
+                                           g_daemon_conf->module_count,
+                                           g_daemon_conf->global.max_connections_per_host,
+                                           g_daemon_conf->global.auth_lockout_threshold,
+                                           g_daemon_conf->global.auth_lockout_duration_sec);
+    if (!g_daemon_limits)
+      log_message(LOG_LEVEL_WARNING,
+                  "daemon: could not allocate the shared connection registry; per-module / "
+                  "per-host caps and the cross-process auth lockout are disabled (the global "
+                  "'max connections' cap and host ACLs still apply)");
   } else {
     if (!configure_authorization(opts.destination_root)) {
       char* escaped = output_escape(opts.destination_root, false);
@@ -1167,6 +1261,8 @@ int main(int argc, char* argv[]) {
   }
   if (g_daemon_conf)
     server_set_max_connections(g_server, (unsigned int)g_daemon_conf->global.max_connections);
+  if (g_daemon_limits)
+    server_set_limit_registry(g_server, g_daemon_limits);
   if (opts.use_tls) {
     if (!opts.tls_cert || !opts.tls_key || !opts.tls_ca || !opts.client_cn) {
       fprintf(stderr, "Error: --tls requires --cert, --key, --ca, and --client-cn\n");
@@ -1206,6 +1302,8 @@ int main(int argc, char* argv[]) {
   release_authorization();
 
 out:
+  daemon_limits_destroy(g_daemon_limits);
+  g_daemon_limits = NULL;
   daemon_conf_free(g_daemon_conf);
   g_daemon_conf = NULL;
   credentials_free(g_credentials);

src/shared/config.h

@@ -75,87 +75,209 @@ typedef struct {
  * privilege_super_mode_permitted() in identity.h. */
 typedef enum SuperMode { SUPER_MODE_AUTO = 0, SUPER_MODE_ON = 1, SUPER_MODE_OFF = 2 } SuperMode;
 
+/* ===========================================================================
+ * Config wire-field table (single source of truth for protocol 2.20.0).
+ *
+ * Every field below crosses the wire.  The table is the ONLY place a
+ * serialized field is named: config.h expands CONFIG_WIRE_FIELDS() to declare
+ * the struct member, config_set_defaults() expands it to assign the default,
+ * and config_send_wire_block()/config_receive_with_validate() expand the
+ * per-segment lists to emit/consume the frame in exactly this order.  Do NOT
+ * reorder entries and do NOT change a field's segment/KIND without a
+ * PROTOCOL_VERSION bump: the resulting byte stream is pinned by
+ * test_config_wire_golden().
+ *
+ * Entry layout: X(MEMBER, CTYPE, DEFAULT, KIND)
+ *   MEMBER   struct member name (public; never rename)
+ *   CTYPE    C type of the member
+ *   DEFAULT  default-value expression used by config_set_defaults()
+ *   KIND     wire codec, dispatched to CONFIG_SEND_<KIND>/CONFIG_RECV_<KIND>
+ *            in config.c (strings receive through a ConfigStringBudget).
+ *
+ * Fields with genuinely custom logic keep dedicated helpers but are still
+ * declared here exactly once: the protocol-version handshake (HEADER), the
+ * daemon SCRAM auth username (STR_REDACTED_AUTH), the daemon module name
+ * (STR_MODULE), repeated count+array blocks (BLOCK_*), --copy-as presence
+ * (COPY_AS_*), and the derived --delta / use_xattrs bits (DERIVED_DELTA,
+ * BOOL_XATTR_DERIVE).
+ *
+ * SCOPE: this table covers ONLY the serialized wire frame.  The client CLI
+ * option tables in client_cli.c (OPTION_TABLE / NEGATABLE_OPTIONS) are still
+ * hand-maintained and are deliberately NOT generated from this table: the CLI
+ * surface carries client-only fields and flag/alias/negation semantics that
+ * have no wire representation.  Do not assume the two are folded together.
+ * =========================================================================== */
+#define CONFIG_WIRE_HEADER_FIELDS(X) X(version, char*, str_dup(PROTOCOL_VERSION), STR)
+
+#define CONFIG_WIRE_CORE_FIELDS(X)                                                                 \
+  X(eight_bit_output, bool, false, BOOL_8BIT)                                                      \
+  X(max_alloc, unsigned long long, DEFAULT_MAX_ALLOC, RAW_MAXALLOC)                                \
+  X(send_directory, char*, NULL, STR)                                                              \
+  X(receive_root_directory, char*, NULL, STR)                                                      \
+  X(save_to_disk, bool, false, BOOL)                                                               \
+  X(use_multithreading, bool, false, BOOL)                                                         \
+  X(use_chunk_serialization, bool, false, BOOL)                                                    \
+  X(use_compression, bool, false, BOOL)                                                            \
+  X(use_metadata, bool, false, BOOL)                                                               \
+  X(use_executability, bool, false, BOOL)                                                          \
+  X(compression_level, int, 5, INT)                                                                \
+  X(chunk_size, unsigned long long, DEFAULT_CHUNK_SIZE, RAW)                                       \
+  X(use_sendfile, bool, false, BOOL)
+
+#define CONFIG_WIRE_DELTA_FIELDS(X)                                                                \
+  X(use_delete, bool, false, BOOL)                                                                 \
+  X(use_incremental, bool, false, BOOL)                                                            \
+  X(size_only, bool, false, BOOL)                                                                  \
+  X(ignore_times, bool, false, BOOL)                                                               \
+  X(use_delta, bool, false, DERIVED_DELTA)                                                         \
+  X(delta_block_size, uint32_t, DELTA_BLOCK_SIZE_DEFAULT, RAW)                                     \
+  X(delta_max_file_size, unsigned long long, DELTA_MAX_FILE_SIZE, RAW)
+
+#define CONFIG_WIRE_FILE_OPTIONS_FIELDS(X)                                                         \
+  X(backup, bool, false, BOOL)                                                                     \
+  X(backup_dir, char*, NULL, STR_OPT)                                                              \
+  X(remove_source_files, bool, false, BOOL)                                                        \
+  X(follow_symlinks, bool, false, BOOL)                                                            \
+  X(copy_links, bool, false, BOOL)                                                                 \
+  X(safe_links, bool, false, BOOL)                                                                 \
+  X(copy_unsafe_links, bool, false, BOOL)                                                          \
+  X(preserve_hard_links, bool, false, BOOL)                                                        \
+  X(preserve_acls, bool, false, BOOL)                                                              \
+  X(preserve_xattrs, bool, false, BOOL)                                                            \
+  X(preserve_devices, bool, false, BOOL)                                                           \
+  X(preserve_sparse, bool, false, BOOL)                                                            \
+  X(preserve_specials, bool, false, BOOL)                                                          \
+  X(copy_devices, bool, false, BOOL)                                                               \
+  X(write_devices, bool, false, BOOL)
+
+#define CONFIG_WIRE_SELECTION_FIELDS(X)                                                            \
+  X(ignore_existing, bool, false, BOOL)                                                            \
+  X(existing, bool, false, BOOL)                                                                   \
+  X(update, bool, false, BOOL)                                                                     \
+  X(inplace, bool, false, BOOL)                                                                    \
+  X(delay_updates, bool, false, BOOL)                                                              \
+  X(append, bool, false, BOOL)                                                                     \
+  X(use_fsync, bool, false, BOOL)                                                                  \
+  X(append_verify, bool, false, BOOL)                                                              \
+  X(delete_excluded, bool, false, BOOL)                                                            \
+  X(force_delete, bool, false, BOOL)                                                               \
+  X(delete_missing_args, bool, false, BOOL)                                                        \
+  X(delete_after, bool, false, BOOL)                                                               \
+  X(preallocate, bool, false, BOOL)                                                                \
+  X(max_delete, int, -1, RAW)                                                                      \
+  X(relative, bool, false, BOOL)                                                                   \
+  X(prune_empty_dirs, bool, false, BOOL)                                                           \
+  X(mkpath, bool, false, BOOL)                                                                     \
+  X(delete_during, bool, false, BOOL)                                                              \
+  X(delete_delay, bool, false, BOOL)
+
+#define CONFIG_WIRE_RESUME_FIELDS(X)                                                               \
+  X(temp_dir, char*, NULL, STR_OPT)                                                                \
+  X(partial, bool, false, BOOL)                                                                    \
+  X(partial_dir, char*, NULL, STR_OPT)                                                             \
+  X(suffix, char*, NULL, STR_OPT)                                                                  \
+  X(delete_before, bool, false, BOOL)                                                              \
+  X(checksum, bool, false, BOOL)                                                                   \
+  X(modify_window, int, 0, RAW)                                                                    \
+  X(compress_choice, char*, NULL, STR_KEEP)                                                        \
+  X(chmod_spec, char*, NULL, STR_KEEP)                                                             \
+  X(skip_compress_set, bool, false, BOOL)                                                          \
+  X(skip_compress_count, int, 0, INT_SKIPCOUNT)                                                    \
+  X(skip_compress_suffixes, char**, NULL, BLOCK_SKIP_SUFFIXES)
+
+#define CONFIG_WIRE_BASIS_FIELDS(X)                                                                \
+  X(basis_count, int, 0, INT_BASISCOUNT)                                                           \
+  X(basis_dirs, BasisDest*, NULL, BLOCK_BASIS)
+
+#define CONFIG_WIRE_FUZZY_FIELDS(X) X(fuzzy, bool, false, BOOL)
+
+#define CONFIG_WIRE_CHECKSUM_FIELDS(X)                                                             \
+  X(checksum_algo, int, CHECKSUM_ALGO_XXH64, INT_CHECKSUM_ALGO)                                    \
+  X(checksum_seed, uint64_t, 0, RAW)
+
+#define CONFIG_WIRE_IDENTITY_FIELDS(X)                                                             \
+  X(numeric_ids, bool, false, BOOL)                                                                \
+  X(chown_uid_set, bool, false, BOOL)                                                              \
+  X(chown_uid, int32_t, 0, INT_IDENTITY)                                                           \
+  X(chown_gid_set, bool, false, BOOL)                                                              \
+  X(chown_gid, int32_t, 0, INT_IDENTITY)                                                           \
+  X(usermap_count, int, 0, INT_IDMAPCOUNT)                                                         \
+  X(usermap, IdentityMap*, NULL, BLOCK_IDMAP)                                                      \
+  X(groupmap_count, int, 0, INT_IDMAPCOUNT)                                                        \
+  X(groupmap, IdentityMap*, NULL, BLOCK_IDMAP)
+
+#define CONFIG_WIRE_METADATA_TIMES_FIELDS(X)                                                       \
+  X(preserve_atimes, bool, false, BOOL)                                                            \
+  X(preserve_crtimes, bool, false, BOOL)                                                           \
+  X(omit_dir_times, bool, false, BOOL)                                                             \
+  X(omit_link_times, bool, false, BOOL)
+
+#define CONFIG_WIRE_SYMLINK_TRUST_FIELDS(X)                                                        \
+  X(munge_links, bool, false, BOOL)                                                                \
+  X(keep_dirlinks, bool, false, BOOL)
+
+#define CONFIG_WIRE_XATTR_FIELDS(X) X(fake_super, bool, false, BOOL_XATTR_DERIVE)
+
+#define CONFIG_WIRE_MODULE_FIELDS(X) X(module, char*, NULL, STR_MODULE)
+
+#define CONFIG_WIRE_DAEMON_AUTH_FIELDS(X) X(auth_user, char*, NULL, STR_REDACTED_AUTH)
+
+#define CONFIG_WIRE_ICONV_FIELDS(X) X(iconv_spec, char*, NULL, STR_OPT)
+
+#define CONFIG_WIRE_PRIVILEGE_FIELDS(X) X(super_mode, SuperMode, SUPER_MODE_AUTO, SUPERMODE)
+
+#define CONFIG_WIRE_COPY_AS_FIELDS(X)                                                              \
+  X(copy_as_set, bool, false, COPY_AS_PRESENCE)                                                    \
+  X(copy_as_uid, int32_t, 0, COPY_AS_ID)                                                           \
+  X(copy_as_gid, int32_t, 0, COPY_AS_ID)
+
+/* All serialized fields, in exact wire order.  Concatenating the per-segment
+ * lists here is what keeps the declaration order = the wire order. */
+#define CONFIG_WIRE_FIELDS(X)                                                                      \
+  CONFIG_WIRE_HEADER_FIELDS(X)                                                                     \
+  CONFIG_WIRE_CORE_FIELDS(X)                                                                       \
+  CONFIG_WIRE_DELTA_FIELDS(X)                                                                      \
+  CONFIG_WIRE_FILE_OPTIONS_FIELDS(X)                                                               \
+  CONFIG_WIRE_SELECTION_FIELDS(X)                                                                  \
+  CONFIG_WIRE_RESUME_FIELDS(X)                                                                     \
+  CONFIG_WIRE_BASIS_FIELDS(X)                                                                      \
+  CONFIG_WIRE_FUZZY_FIELDS(X)                                                                      \
+  CONFIG_WIRE_CHECKSUM_FIELDS(X)                                                                   \
+  CONFIG_WIRE_IDENTITY_FIELDS(X)                                                                   \
+  CONFIG_WIRE_METADATA_TIMES_FIELDS(X)                                                             \
+  CONFIG_WIRE_SYMLINK_TRUST_FIELDS(X)                                                              \
+  CONFIG_WIRE_XATTR_FIELDS(X)                                                                      \
+  CONFIG_WIRE_MODULE_FIELDS(X)                                                                     \
+  CONFIG_WIRE_DAEMON_AUTH_FIELDS(X)                                                                \
+  CONFIG_WIRE_ICONV_FIELDS(X)                                                                      \
+  CONFIG_WIRE_PRIVILEGE_FIELDS(X)                                                                  \
+  CONFIG_WIRE_COPY_AS_FIELDS(X)
+
 typedef struct Config {
-  char* version;
-  char* send_directory;
-  char* receive_root_directory;
-  bool save_to_disk;
-  bool use_multithreading;
   /* -j/--threads=N: number of parallel scanner worker threads for the -m
    * pipeline.  0 (the default, also set by bare -j/--threads) means "use the
    * scanner's built-in default" (4).  CLIENT-ONLY: it is a local scheduling
    * concern and is NEVER serialized into the wire config frame. */
   int scanner_threads;
-  bool use_chunk_serialization;
-  bool use_compression;
-  bool use_sendfile;
-  bool use_metadata;
-  bool use_executability;
   bool metadata_explicitly_disabled;
   bool show_progress;
   bool dry_run;
-  bool remove_source_files;
-  bool use_delete;
-  int compression_level;
   int compression_threads;
-  unsigned long long chunk_size;
   int ssh_port;
   TransportType transport;
   char* ssh_destination;
-  /* Daemon module selection (Wave A, protocol 2.15.0).  Client-composed from a
-   * host::module/path destination; NULL or "" means "no module" (the ordinary
-   * standalone-server path).  Crosses the wire as a trailing config-frame
-   * string so the daemon can look the module up in its own config and confine
-   * the connection to the module's root (never a client-chosen root). */
-  char* module;
-  /* Daemon password authentication (A7 remediation, protocol 2.19.0).
-   * Client-composed from a --password-file whose first meaningful line is
-   * `user:password`: the client sends ONLY the username in the config frame
-   * (auth_user); the literal password is kept in auth_password CLIENT-SIDE for
-   * the duration of the SCRAM challenge/response and is NEVER serialized.  Both
-   * are NULL when the client has no credentials to present; a module WITHOUT
-   * `auth users` stays open and the server ignores any credentials that do
-   * arrive (the client sends them opportunistically and the server decides). */
-  char* auth_user;
   char* auth_password;
   /* Client-only path of --password-file (never crosses the wire; it is read to
    * populate auth_user/auth_password before connecting). */
   char* password_file;
   char* fastsync_server_path;
-  /* --iconv=CONVERT_SPEC (protocol 2.16.0, rsync compatibility): convert the
-   * charset of FILE NAMES at the wire boundary.  CONVERT_SPEC is
-   * "LOCAL[,REMOTE]": LOCAL is the charset of our own file names, REMOTE is
-   * the remote side's charset and defaults to LOCAL.  The sender converts
-   * every path LOCAL->REMOTE before transmitting it; the receiver converts
-   * every received path back REMOTE->LOCAL before creating/writing it.  The
-   * FULL SPEC crosses the wire as a trailing config-frame string so each end
-   * derives its own LOCAL and the wire (REMOTE) charset symmetrically.  NULL
-   * (or "") means no conversion: identity with zero overhead.  See charset.c
-   * and the PROTOCOL_VERSION note below. */
-  char* iconv_spec;
   char** exclude_patterns;
   int exclude_count;
   char** include_patterns;
   int include_count;
   unsigned long long max_size;
   unsigned long long min_size;
-  unsigned long long max_alloc;
-  bool use_incremental;
-  bool ignore_times;
-  bool size_only;
-  bool use_delta;
   bool whole_file;
-  /* -y/--fuzzy: when a file must be transferred and the destination holds no
-   * usable file at the exact path, the receiver may reuse a SIMILAR-named
-   * existing regular file in the same destination directory as the delta
-   * basis so the sender transmits only the differences.  Crosses the wire
-   * (the receiver performs the candidate search); the CLI implies
-   * --incremental + --delta because the similar-basis only matters on the
-   * receiver-driven delta path.  Off by default. */
-  bool fuzzy;
-  int modify_window;
-  uint32_t delta_block_size;
-  unsigned long long delta_max_file_size;
   bool use_tls;
   char* server_host;
   int server_port;
@@ -170,18 +292,10 @@ typedef struct Config {
   /* --contimeout: connect()/accept timeout, transport layer only. */
   int contimeout;
   bool quiet;
-  bool backup;
-  char* backup_dir;
   bool stats;
   int max_depth;
   FILE* log_file;
-  bool follow_symlinks;
-  bool partial;
 
-  // Issue #120: Symlink handling
-  bool copy_links;
-  bool safe_links;
-  bool copy_unsafe_links;
   /* Phase 4 symlink-trust.  -k/--copy-dirlinks and --munge-links are
    * CLIENT/sender-side only (they decide how the SENDER scans and rewrites
    * symlinks; the receiver never reads them), so they never cross the wire.
@@ -189,31 +303,6 @@ typedef struct Config {
    * symlink-to-directory as a directory) and CROSSES the wire along with
    * --munge-links (so the receiver knows to unmunge). */
   bool copy_dirlinks; /* client-only, sender-side (-k) */
-  bool munge_links;   /* crosses the wire */
-  bool keep_dirlinks; /* crosses the wire (-K) */
-
-  // Issue #121: Extended metadata preservation
-  bool preserve_hard_links;
-  bool preserve_acls;
-  bool preserve_xattrs;
-  bool preserve_devices;
-  bool preserve_sparse;
-  /* Phase 4 special/devices: preserve special files (FIFOs, sockets) and device
-   * nodes on the destination by recreating them (mknod/mkfifo) instead of
-   * transferring content.  preserve_specials mirrors rsync --specials (the
-   * special-file half of -D); preserve_devices mirrors --devices (the device
-   * half of -D); both CROSS the wire so the receiver knows a special/device
-   * entry must be recreated rather than written as a regular file. */
-  bool preserve_specials;
-  /* --copy-devices: copy the CONTENT of a source device as an ordinary regular
-   * file on the destination (rsync's non-privileged safe mode), instead of
-   * recreating the device node.  CROSSES the wire (receiver treats the entry as
-   * a regular file, which is the default, so this is belt-and-braces). */
-  bool copy_devices;
-  /* --write-devices: write the received data directly INTO an existing device
-   * node on the destination instead of creating a regular file.  Dangeroud;
-   * see RSYNC_COMPAT.md for the tight gating.  CROSSES the wire. */
-  bool write_devices;
 
   // Issue #122: Output/logging options
   bool itemize_changes;
@@ -223,57 +312,17 @@ typedef struct Config {
   int debug_level;
   bool list_only;
   bool human_readable;
-  bool eight_bit_output;
 
-  // Issue #127: Transfer modes
-  bool existing;
-  bool ignore_existing;
-  bool update;
-  bool inplace;
-  bool delay_updates;
-  bool use_fsync;
-  bool append;
-  bool append_verify;
-  /* --preallocate: allocates the destination file's full expected space up
-   * front (before any data is written) so a transfer that would overflow disk
-   * fails fast at allocation time and the file is laid out contiguously,
-   * avoiding fragmentation.  Receiver-side, crosses the wire. */
-  bool preallocate;
-
-  // Issue #128: Extended delete options
-  /* --delete-excluded: also delete destination entries that were excluded on
-   * the source.  Default (off) matches rsync: excluded paths are protected from
-   * deletion.  Crosses the wire (the sender encodes the choice by whether it
-   * transmits a protected-prefix list with the keep-set manifest). */
-  bool delete_excluded;
-  bool delete_after;
-  /* --max-delete=NUM: the receiver refuses to delete more than NUM entries per
-   * run (all-or-nothing: when the extras would exceed NUM nothing is removed and
-   * the transfer fails with a distinct error).  -1 == no client limit (the
-   * server hard bound MAX_SERVER_DELETE_COUNT still applies). */
-  int max_delete;
   /* --ignore-errors (client-only, never serialized): a sender-side source I/O
    * error (an unreadable directory during the scan) normally aborts the run so
    * no deletion happens; with --ignore-errors the scan continues and the
    * (partial) keep-set is still transmitted so the deletion runs. */
   bool ignore_errors;
-  /* --force (receiver-side): a regular file may replace a destination
-   * directory by removing that (possibly non-empty, symlink-safe) directory
-   * tree first, instead of failing the write.  Crosses the wire. */
-  bool force_delete;
   /* --ignore-missing-args (client-only, never serialized): a --files-from
    * entry that does not exist under the source is silently skipped instead of
    * failing the run.  Sender-side only: nothing is sent for it and it never
    * enters the keep-set.  Implied by --delete-missing-args. */
   bool ignore_missing_args;
-  /* --delete-missing-args: implies --ignore-missing-args; additionally each
-   * missing entry's destination mirror (computed like a present entry's wire
-   * path) is deleted receiver-side.  Crosses the wire and is gated by the
-   * server's --allow-delete policy like --delete.  rsync-parity: independent
-   * of ordinary --delete processing (it does not imply --delete); a non-empty
-   * directory mirror is only removed with --force or --delete in effect, and
-   * the missing-args deletions are not counted toward --max-delete. */
-  bool delete_missing_args;
 
   // Issue #129: Advanced file selection. These fields are CLIENT-ONLY: they are
   // never serialized to the wire (the receiver must not learn them).
@@ -283,23 +332,14 @@ typedef struct Config {
   bool from0;           /* -0/--from0: NUL-delimited *-from files */
   bool cvs_exclude;     /* -C/--cvs-exclude: standard CVS ignore set */
   bool per_dir_filter;  /* -F: apply per-directory .rsync-filter files */
-  bool prune_empty_dirs;
   bool one_file_system; /* -x/--one-file-system: do not cross filesystem boundaries */
-  /* -R/--relative: crosses the wire; with --files-from listed entries keep
-   * their bare relative destination path (no source-root mirror prefix). */
-  bool relative;
   /* --no-implied-dirs: client-only.  With -R + --files-from, refuse to place a
    * listed file whose ancestor directory is not itself explicitly listed. */
   bool no_implied_dirs;
   /* -d/--dirs: client-only.  Transfer the directory entries named by the
    * source argument / --files-from list without recursing into contents. */
   bool dirs;
-  /* --mkpath: crosses the wire.  Tells the server to create the destination
-   * root directory (and missing leading components below its authorized root)
-   * at connection start instead of requiring it to already exist. */
-  bool mkpath;
 
-  // Issue #130: Remote shell/connection options
   /* -e/--rsh: the remote-shell program used to establish the SSH transport.
    * NULL means the default "ssh".  Client-only launch concern: NEVER crosses
    * the wire (it is not meaningful to the daemon/server handshake). */
@@ -312,7 +352,6 @@ typedef struct Config {
    * concern: NEVER crosses the wire. */
   int outbuf;
   bool old_args;
-  char* temp_dir;
   /* --remote-option=OPT (Phase 5, long form only): one or more extra command-line
    * options to append to the REMOTE server invocation over SSH.  CLIENT-ONLY:
    * they are composed into the remote command line by ssh_build_remote_command()
@@ -321,34 +360,6 @@ typedef struct Config {
    * do NOT cross the wire and are never parsed on the receiver process. */
   char** remote_options;
   int remote_option_count;
-  /* Alternate basis directories, ordered by command-line appearance.  Each
-   * entry's type selects compare/copy/link behavior on an exact match.  These
-   * cross the wire so the receiver can consult them; they are interpreted
-   * relative to the destination root and confined there. */
-  BasisDest* basis_dirs;
-  int basis_count;
-
-  // PR #174: Partial transfer resumption
-  char* partial_dir;
-
-  // PR #178: Backup versioning
-  char* suffix;
-
-  // PR #179: Delete policies
-  bool delete_before;
-
-  /* rsync deletion-timing family (real from Phase 3).  At most one of
-     delete_before / delete_during / delete_delay / delete_after may be set, and
-     only together with use_delete (the CLI implies --delete for each of them).
-     delete_before and delete_during select the EARLY engine mode: the keep-set
-     manifest is transmitted before any file data and extras are removed then,
-     acknowledged, before the first data byte.  delete_delay and delete_after
-     select the LATE commit mode: extras are removed only after the whole
-     transfer has succeeded (plain --delete keeps this mode).  The exact
-     semantics and the divergences from rsync are documented in RSYNC_COMPAT.md
-     and in config_delete_timing_early() below. */
-  bool delete_during;
-  bool delete_delay;
 
   // PR #181: IPv6 and bind address
   char* address;
@@ -370,119 +381,19 @@ typedef struct Config {
    * MOTD is shown when a daemon offers one). */
   bool no_motd;
 
-  // PR #183: Checksum comparison
-  bool checksum;
-
-  // PR #184: Compression algorithm negotiation
-  char* compress_choice;
-  char* chmod_spec;
-
-  /* --checksum-choice / --cc and --checksum-seed.  checksum_algo is the id of
-   * the whole-file content-digest algorithm used by the per-file --incremental
-   * handshake (sender computes it, receiver compares it to skip unchanged
-   * files) and by the basis-dir content verification.  checksum_seed is passed
-   * to xxHash64 (and to the delta block strong hash, low 32 bits); md5 has no
-   * seed so it is ignored there.  Both cross the wire: the receiver MUST hash
-   * the on-disk old file with the same algorithm and seed to reach a matching
-   * digest.  Defaults (XXH64 / seed 0) reproduce the pre-existing behavior
-   * byte-for-byte. */
-  int checksum_algo;      /* ChecksumAlgo, default CHECKSUM_ALGO_XXH64 */
-  uint64_t checksum_seed; /* default 0 */
-
-  char** skip_compress_suffixes;
-  int skip_compress_count;
-  bool skip_compress_set;
-
-  // Issue #131: Identity mapping.  These configure whether and how the receiver
-  // applies ownership when it is actually preserved/applied.  ALL of them cross
-  // the wire (protocol 2.11.0) so the receiver resolves and applies ownership
-  // with the exact policy the client requested.  Plain -M/--preserve still does
-  // NOT apply ownership (FastSync's deliberate conservative default); it is
-  // only attempted when at least one of these is set (see identity.h).
-  /* --numeric-ids: no name lookup, use the transmitted numeric ids raw. */
-  bool numeric_ids;
-  /* --chown USER (owner) override; IDENTITY_CURRENT = the receiver's euid. */
-  bool chown_uid_set;
-  int32_t chown_uid;
-  /* --chown :GROUP (group) override; IDENTITY_CURRENT = the receiver's egid. */
-  bool chown_gid_set;
-  int32_t chown_gid;
-  /* --usermap / --groupmap entries, in order (first match wins). */
-  IdentityMap* usermap;
-  int usermap_count;
-  IdentityMap* groupmap;
-  int groupmap_count;
-
-  /* --super / --no-super (P7 Wave E, protocol 2.18.0): receiver-side privilege
-   * policy for super-user activities confined below the authorized receive
-   * root.  SUPER_MODE_AUTO (default) preserves the pre-existing best-effort
-   * behavior: the confined super-user operation is ALWAYS attempted and an
-   * unprivileged attempt is refused by the kernel and skipped per entry.
-   * SUPER_MODE_ON (--super) explicitly REQUESTS those activities (char/block
-   * device-node creation, --write-devices); it does NOT imply --numeric-ids and
-   * never enables ownership application on its own.  SUPER_MODE_OFF
-   * (--no-super) FORBIDS them even when running as root.  FastSync NEVER
-   * elevates privileges (no setuid/seteuid/setgid) and never bypasses the
-   * fd-relative confinement (file_open_secure_parent, O_NOFOLLOW, root checks);
-   * --super only permits an attempt that is already confined.  Crosses the wire
-   * as a trailing int so the receiver can enforce the policy.  See
-   * privilege_super_permitted() and identity_ownership_requested() in
-   * identity.h. */
-  SuperMode super_mode;
-
   // Receiver-side runtime staging registry for --delay-updates.  Never sent
   // over the wire and never set on the sender side.
   DelayUpdatesContext* delay_context;
 
-  // Phase 4: metadata time preservation.  -U/--atimes and -N/--crtimes capture
-  // and transmit the source access / birth time (both sender and receiver
-  // effect, so they CROSS the wire).  --omit-dir-times/-O and
-  // --omit-link-times/-J are receiver-side prefs (CROSS the wire).  Their
-  // exact capture/transmit/apply semantics are documented in RSYNC_COMPAT.md.
-  /* -U/--atimes: preserve source access times on the destination. */
-  bool preserve_atimes;
-  /* -N/--crtimes: capture+transmit source birth time; see RSYNC_COMPAT for the
-   * receiver not-applied divergence. */
-  bool preserve_crtimes;
-  /* -O/--omit-dir-times: do not apply mtimes to directories. */
-  bool omit_dir_times;
-  /* -J/--omit-link-times: do not apply times to symlinks. */
-  bool omit_link_times;
   /* --open-noatime: CLIENT-ONLY (never crosses the wire).  The sender opens
    * source files with O_NOATIME so reading for transfer does not bump the
    * source access time. */
   bool open_noatime;
 
-  // Phase 4: xattr / ACL / fake-super preservation.
-  /* -X/--xattrs and -A/--acls toggle the sender's capture and the receiver's
-   * application of per-file extended attributes (xattrs).  Both cross the wire:
-   * the sender only transmits the bounded, whitelisted attribute set it
-   * captures and the receiver re-validates namespaces/sizes before applying
-   * fd-relative.  With neither set (the default) no xattr block is sent, so the
-   * wire is byte-identical to prior protocol versions for unaffected runs. */
   /* true when preserve_xattrs || preserve_acls; the sender/receiver gate the
    * xattr wire block on this single flag. */
   bool use_xattrs;
-  /* --fake-super: receiver-only.  When set, each written file additionally gets
-   * a reserved user.fastsync.stat xattr recording the source uid/gid/mode/mtime
-   * so a later privileged restore could re-apply them.  Crosses the wire. */
-  bool fake_super;
-  /* --copy-as=USER[:GROUP] (P7 Wave E, protocol 2.18.0).  Safe-subset
-   * implementation, a documented divergence from rsync's real identity switch:
-   * the receiver does NOT change its process credentials (FastSync's receiver
-   * is multithreaded, so a setuid/seteuid drop would be unsafe).  Instead the
-   * receiver FORCES the ownership of every entry it writes to copy_as_uid /
-   * copy_as_gid through the existing confined, fd-relative identity path
-   * (fchown/fchownat), which REQUIRES receiver privilege (root); an
-   * unprivileged receiver REFUSES the whole transfer up front at the config
-   * handshake (never a silent wrong-ownership result).  All three fields CROSS
-   * the wire as a trailing config-frame block so the receiver learns the
-   * requested ids; see the PROTOCOL_VERSION note below. */
-  bool copy_as_set;
-  int32_t copy_as_uid;
-  int32_t copy_as_gid;
 
-  // Phase 5: --trust-sender
   /* Long-form-only, receiver-local policy.  rsync's --trust-sender tells the
    * receiving side to trust that the sender already produced a sane file list,
    * relaxing the receiver's own up-front re-validation of every incoming path.
@@ -501,7 +412,6 @@ typedef struct Config {
    * default; only relaxes validation when explicitly requested. */
   bool trust_sender;
 
-  // Phase 6: --stop-after / --stop-at
   /* Client-only sender-side transfer stop deadlines.  --stop-after=MINS stops
    * the transfer after a number of elapsed minutes (checked against
    * CLOCK_MONOTONIC so clock changes do not skew it); --stop-at=TIME stops at
@@ -513,7 +423,6 @@ typedef struct Config {
   time_t stop_at;      /* --stop-at=... absolute wall-clock deadline */
   bool stop_at_set;    /* true when --stop-at was given */
 
-  // Phase 6: --write-batch / --only-write-batch / --read-batch
   /* Client-only residual-batch paths.  A residual batch is a self-contained
    * single-file record of the whole source tree (full file images using the
    * chunk codec), independent of any live server.  --write-batch=FILE runs the
@@ -525,6 +434,196 @@ typedef struct Config {
   char* write_batch;      /* --write-batch=FILE path, or NULL */
   char* only_write_batch; /* --only-write-batch=FILE path, or NULL */
   char* read_batch;       /* --read-batch=FILE path, or NULL */
+
+  /* ===================================================================
+   * Serialized wire fields.  Their members, defaults and send/receive
+   * sequence are generated from the CONFIG_WIRE_*_FIELDS table above (the
+   * single source of truth); they are declared here in exact wire order.
+   * The per-field notes were moved here from their original positions and
+   * are listed in wire order.
+   * =================================================================== */
+  /* copy_links */
+  // Issue #120: Symlink handling
+  /* preserve_hard_links */
+  // Issue #121: Extended metadata preservation
+  /* preserve_specials */
+  /* Phase 4 special/devices: preserve special files (FIFOs, sockets) and device
+   * nodes on the destination by recreating them (mknod/mkfifo) instead of
+   * transferring content.  preserve_specials mirrors rsync --specials (the
+   * special-file half of -D); preserve_devices mirrors --devices (the device
+   * half of -D); both CROSS the wire so the receiver knows a special/device
+   * entry must be recreated rather than written as a regular file. */
+  /* copy_devices */
+  /* --copy-devices: copy the CONTENT of a source device as an ordinary regular
+   * file on the destination (rsync's non-privileged safe mode), instead of
+   * recreating the device node.  CROSSES the wire (receiver treats the entry as
+   * a regular file, which is the default, so this is belt-and-braces). */
+  /* write_devices */
+  /* --write-devices: write the received data directly INTO an existing device
+   * node on the destination instead of creating a regular file.  Dangeroud;
+   * see RSYNC_COMPAT.md for the tight gating.  CROSSES the wire. */
+  /* existing */
+  // Issue #127: Transfer modes
+  /* delete_excluded */
+  /* --delete-excluded: also delete destination entries that were excluded on
+   * the source.  Default (off) matches rsync: excluded paths are protected from
+   * deletion.  Crosses the wire (the sender encodes the choice by whether it
+   * transmits a protected-prefix list with the keep-set manifest). */
+  /* force_delete */
+  /* --force (receiver-side): a regular file may replace a destination
+   * directory by removing that (possibly non-empty, symlink-safe) directory
+   * tree first, instead of failing the write.  Crosses the wire. */
+  /* delete_missing_args */
+  /* --delete-missing-args: implies --ignore-missing-args; additionally each
+   * missing entry's destination mirror (computed like a present entry's wire
+   * path) is deleted receiver-side.  Crosses the wire and is gated by the
+   * server's --allow-delete policy like --delete.  rsync-parity: independent
+   * of ordinary --delete processing (it does not imply --delete); a non-empty
+   * directory mirror is only removed with --force or --delete in effect, and
+   * the missing-args deletions are not counted toward --max-delete. */
+  /* preallocate */
+  /* --preallocate: allocates the destination file's full expected space up
+   * front (before any data is written) so a transfer that would overflow disk
+   * fails fast at allocation time and the file is laid out contiguously,
+   * avoiding fragmentation.  Receiver-side, crosses the wire. */
+  /* max_delete */
+  /* --max-delete=NUM: the receiver refuses to delete more than NUM entries per
+   * run (all-or-nothing: when the extras would exceed NUM nothing is removed and
+   * the transfer fails with a distinct error).  -1 == no client limit (the
+   * server hard bound MAX_SERVER_DELETE_COUNT still applies). */
+  /* relative */
+  /* -R/--relative: crosses the wire; with --files-from listed entries keep
+   * their bare relative destination path (no source-root mirror prefix). */
+  /* mkpath */
+  /* --mkpath: crosses the wire.  Tells the server to create the destination
+   * root directory (and missing leading components below its authorized root)
+   * at connection start instead of requiring it to already exist. */
+  /* delete_during */
+  /* rsync deletion-timing family (real from Phase 3).  At most one of
+     delete_before / delete_during / delete_delay / delete_after may be set, and
+     only together with use_delete (the CLI implies --delete for each of them).
+     delete_before and delete_during select the EARLY engine mode: the keep-set
+     manifest is transmitted before any file data and extras are removed then,
+     acknowledged, before the first data byte.  delete_delay and delete_after
+     select the LATE commit mode: extras are removed only after the whole
+     transfer has succeeded (plain --delete keeps this mode).  The exact
+     semantics and the divergences from rsync are documented in RSYNC_COMPAT.md
+     and in config_delete_timing_early() below. */
+  /* partial_dir */
+  // PR #174: Partial transfer resumption
+  /* suffix */
+  // PR #178: Backup versioning
+  /* delete_before */
+  // PR #179: Delete policies
+  /* checksum */
+  // PR #183: Checksum comparison
+  /* compress_choice */
+  // PR #184: Compression algorithm negotiation
+  /* basis_dirs */
+  /* Alternate basis directories, ordered by command-line appearance.  Each
+   * entry's type selects compare/copy/link behavior on an exact match.  These
+   * cross the wire so the receiver can consult them; they are interpreted
+   * relative to the destination root and confined there. */
+  /* fuzzy */
+  /* -y/--fuzzy: when a file must be transferred and the destination holds no
+   * usable file at the exact path, the receiver may reuse a SIMILAR-named
+   * existing regular file in the same destination directory as the delta
+   * basis so the sender transmits only the differences.  Crosses the wire
+   * (the receiver performs the candidate search); the CLI implies
+   * --incremental + --delta because the similar-basis only matters on the
+   * receiver-driven delta path.  Off by default. */
+  /* checksum_algo / checksum_seed */
+  /* --checksum-choice / --cc and --checksum-seed.  checksum_algo is the id of
+   * the whole-file content-digest algorithm used by the per-file --incremental
+   * handshake (sender computes it, receiver compares it to skip unchanged
+   * files) and by the basis-dir content verification.  checksum_seed is passed
+   * to xxHash64 (and to the delta block strong hash, low 32 bits); md5 has no
+   * seed so it is ignored there.  Both cross the wire: the receiver MUST hash
+   * the on-disk old file with the same algorithm and seed to reach a matching
+   * digest. */
+  /* munge_links / keep_dirlinks */
+  /* Phase 4 symlink-trust: both cross the wire (the receiver unmunges symlink
+   * targets and, with -K, follows an in-root destination symlink-to-directory);
+   * -k/--copy-dirlinks is sender-only and is never serialized. */
+  /* numeric_ids */
+  /* --numeric-ids: no name lookup, use the transmitted numeric ids raw. */
+  /* chown_uid_set */
+  /* --chown USER (owner) override; IDENTITY_CURRENT = the receiver's euid. */
+  /* chown_gid_set */
+  /* --chown :GROUP (group) override; IDENTITY_CURRENT = the receiver's egid. */
+  /* usermap */
+  /* --usermap / --groupmap entries, in order (first match wins). */
+  /* preserve_atimes */
+  /* -U/--atimes: preserve source access times on the destination. */
+  /* preserve_crtimes */
+  /* -N/--crtimes: capture+transmit source birth time; see RSYNC_COMPAT for the
+   * receiver not-applied divergence. */
+  /* omit_dir_times */
+  /* -O/--omit-dir-times: do not apply mtimes to directories. */
+  /* omit_link_times */
+  /* -J/--omit-link-times: do not apply times to symlinks. */
+  /* fake_super */
+  /* --fake-super: receiver-only.  When set, each written file additionally gets
+   * a reserved user.fastsync.stat xattr recording the source uid/gid/mode/mtime
+   * so a later privileged restore could re-apply them.  Crosses the wire. */
+  /* module */
+  /* Daemon module selection (Wave A, protocol 2.15.0).  Client-composed from a
+   * host::module/path destination; NULL or "" means "no module" (the ordinary
+   * standalone-server path).  Crosses the wire as a trailing config-frame
+   * string so the daemon can look the module up in its own config and confine
+   * the connection to the module's root (never a client-chosen root). */
+  /* auth_user */
+  /* Daemon password authentication (A7 remediation, protocol 2.19.0).
+   * Client-composed from a --password-file whose first meaningful line is
+   * `user:password`: the client sends ONLY the username in the config frame
+   * (auth_user); the literal password is kept in auth_password CLIENT-SIDE for
+   * the duration of the SCRAM challenge/response and is NEVER serialized.  Both
+   * are NULL when the client has no credentials to present; a module WITHOUT
+   * `auth users` stays open and the server ignores any credentials that do
+   * arrive (the client sends them opportunistically and the server decides). */
+  /* iconv_spec */
+  /* --iconv=CONVERT_SPEC (protocol 2.16.0, rsync compatibility): convert the
+   * charset of FILE NAMES at the wire boundary.  CONVERT_SPEC is
+   * "LOCAL[,REMOTE]": LOCAL is the charset of our own file names, REMOTE is
+   * the remote side's charset and defaults to LOCAL.  The sender converts
+   * every path LOCAL->REMOTE before transmitting it; the receiver converts
+   * every received path back REMOTE->LOCAL before creating/writing it.  The
+   * FULL SPEC crosses the wire as a trailing config-frame string so each end
+   * derives its own LOCAL and the wire (REMOTE) charset symmetrically.  NULL
+   * (or "") means no conversion: identity with zero overhead.  See charset.c
+   * and the PROTOCOL_VERSION note below. */
+  /* super_mode */
+  /* --super / --no-super (P7 Wave E, protocol 2.18.0): receiver-side privilege
+   * policy for super-user activities confined below the authorized receive
+   * root.  SUPER_MODE_AUTO (default) preserves the pre-existing best-effort
+   * behavior: the confined super-user operation is ALWAYS attempted and an
+   * unprivileged attempt is refused by the kernel and skipped per entry.
+   * SUPER_MODE_ON (--super) explicitly REQUESTS those activities (char/block
+   * device-node creation, --write-devices); it does NOT imply --numeric-ids and
+   * never enables ownership application on its own.  SUPER_MODE_OFF
+   * (--no-super) FORBIDS them even when running as root.  FastSync NEVER
+   * elevates privileges (no setuid/seteuid/setgid) and never bypasses the
+   * fd-relative confinement (file_open_secure_parent, O_NOFOLLOW, root checks);
+   * --super only permits an attempt that is already confined.  Crosses the wire
+   * as a trailing int so the receiver can enforce the policy.  See
+   * privilege_super_permitted() and identity_ownership_requested() in
+   * identity.h. */
+  /* copy_as_set */
+  /* --copy-as=USER[:GROUP] (P7 Wave E, protocol 2.18.0).  Safe-subset
+   * implementation, a documented divergence from rsync's real identity switch:
+   * the receiver does NOT change its process credentials (FastSync's receiver
+   * is multithreaded, so a setuid/seteuid drop would be unsafe).  Instead the
+   * receiver FORCES the ownership of every entry it writes to copy_as_uid /
+   * copy_as_gid through the existing confined, fd-relative identity path
+   * (fchown/fchownat), which REQUIRES receiver privilege (root); an
+   * unprivileged receiver REFUSES the whole transfer up front at the config
+   * handshake (never a silent wrong-ownership result).  All three fields CROSS
+   * the wire as a trailing config-frame block so the receiver learns the
+   * requested ids; see the PROTOCOL_VERSION note below. */
+
+#define CONFIG_STRUCT_MEMBER(name, ctype, def, kind) ctype name;
+  CONFIG_WIRE_FIELDS(CONFIG_STRUCT_MEMBER)
+#undef CONFIG_STRUCT_MEMBER
 } Config;
 
 /* Phase 5 (remote-option wave): 2.13.0 -> 2.14.0.
@@ -699,6 +798,10 @@ void config_delete(Config* config);
 void config_burn_auth(Config* config);
 
 bool config_send(int file_descriptor, const Config* config);
+/* Emit the config frame BODY (every serialized field, in wire order) without
+ * the trailing STATUS_OK handshake.  config_send() is this plus the handshake;
+ * the wire-compatibility golden test uses it to hash the exact byte stream. */
+bool config_send_wire_block(int file_descriptor, const Config* config);
 Config* config_receive(int file_descriptor);
 bool config_is_remote_dest(const char* s);
 void config_parse_ssh_dest(Config* config);

src/shared/daemon_conf.c

@@ -190,6 +190,26 @@ static bool store_max_connections(int* slot, const char* value, const char* modu
   return true;
 }
 
+/* Parse a non-negative concurrency cap where 0 means unlimited/disabled
+ * (per-module `max connections`, `max connections per host`,
+ * `auth lockout threshold`).  Negative/garbage/oversized values are rejected. */
+static bool store_optional_cap(int* slot, const char* value, int max_value, const char* key,
+                               const char* module_name, char* err, size_t err_size) {
+  char* end = NULL;
+  errno = 0;
+  long n = strtol(value, &end, 10);
+  if (*value == '\0' || errno != 0 || *end != '\0' || n < 0 || n > max_value) {
+    if (module_name)
+      set_error(err, err_size, "module '%s': invalid '%s' '%s' (must be 0-%d)", module_name, key,
+                value, max_value);
+    else
+      set_error(err, err_size, "invalid '%s' '%s' (must be 0-%d)", key, value, max_value);
+    return false;
+  }
+  *slot = (int)n;
+  return true;
+}
+
 /* Parse an `auth failure delay` value: 0 (disabled) through the configured cap. */
 static bool store_auth_failure_delay(int* slot, const char* value, char* err, size_t err_size) {
   char* end = NULL;
@@ -227,6 +247,9 @@ DaemonConf* daemon_conf_create(void) {
   conf->global.port = DAEMON_CONF_DEFAULT_PORT;
   conf->global.max_connections = DAEMON_CONF_DEFAULT_MAX_CONNECTIONS;
   conf->global.auth_failure_delay_ms = DAEMON_CONF_DEFAULT_AUTH_FAILURE_DELAY_MS;
+  conf->global.max_connections_per_host = DAEMON_CONF_DEFAULT_MAX_CONNECTIONS_PER_HOST;
+  conf->global.auth_lockout_threshold = DAEMON_CONF_DEFAULT_AUTH_LOCKOUT_THRESHOLD;
+  conf->global.auth_lockout_duration_sec = DAEMON_CONF_DEFAULT_AUTH_LOCKOUT_DURATION_SEC;
   return conf;
 }
 
@@ -312,8 +335,20 @@ static bool apply_global_key(DaemonConf* conf, char* key, const char* value, boo
   }
   if (key_equals(key, "max connections"))
     return store_max_connections(&conf->global.max_connections, value, NULL, err, err_size);
+  if (key_equals(key, "max connections per host"))
+    return store_optional_cap(&conf->global.max_connections_per_host, value,
+                              DAEMON_CONF_MAX_CONCURRENCY_LIMIT, "max connections per host", NULL,
+                              err, err_size);
   if (key_equals(key, "auth failure delay"))
     return store_auth_failure_delay(&conf->global.auth_failure_delay_ms, value, err, err_size);
+  if (key_equals(key, "auth lockout threshold"))
+    return store_optional_cap(&conf->global.auth_lockout_threshold, value,
+                              DAEMON_CONF_MAX_CONCURRENCY_LIMIT, "auth lockout threshold", NULL,
+                              err, err_size);
+  if (key_equals(key, "auth lockout duration"))
+    return store_optional_cap(&conf->global.auth_lockout_duration_sec, value,
+                              DAEMON_CONF_MAX_AUTH_LOCKOUT_DURATION_SEC, "auth lockout duration",
+                              NULL, err, err_size);
   if (key_equals(key, "hosts allow"))
     return store_host_list(&conf->global.hosts_allow, &conf->global.hosts_allow_count, value,
                            "hosts allow", NULL, replace_hosts, err, err_size);
@@ -400,7 +435,8 @@ static bool apply_module_key(DaemonModule* module, char* key, char* value, char*
     return true;
   }
   if (key_equals(key, "max connections"))
-    return store_max_connections(&module->max_connections, value, module->name, err, err_size);
+    return store_optional_cap(&module->max_connections, value, DAEMON_CONF_MAX_CONCURRENCY_LIMIT,
+                              "max connections", module->name, err, err_size);
   if (key_equals(key, "hosts allow"))
     return store_host_list(&module->hosts_allow, &module->hosts_allow_count, value, "hosts allow",
                            false, module->name, err, err_size);
@@ -444,6 +480,11 @@ static int open_module(DaemonConf* conf, int* current_module, const char* name,
     set_error(err, err_size, "duplicate module '%s'", name);
     return -1;
   }
+  if (conf->module_count >= DAEMON_CONF_MAX_MODULES) {
+    set_error(err, err_size, "too many modules (limit %d); module '%s' rejected",
+              DAEMON_CONF_MAX_MODULES, name);
+    return -1;
+  }
   DaemonModule* grown =
       realloc(conf->modules, (size_t)(conf->module_count + 1) * sizeof(DaemonModule));
   if (!grown) {

src/shared/daemon_conf.h

@@ -52,11 +52,10 @@ typedef struct DaemonModule {
                         activities.  Without it the daemon refuses all of them. */
   char** auth_users; /* `auth users = a,b`; Wave B credential list */
   int auth_user_count;
-  /* `max connections = N` (optional per-module cap).  0 means "not set"
+  /* `max connections = N` (optional per-module cap).  0 means unlimited.  The
-   * (inherit the global cap).  Parsed, stored, and validated, but NOT enforced
+   * per-connection child records the selected module in the shared registry
-   * per-module: connections are counted in the accept-loop parent before the
+   * (daemon_limits.c) once the config frame names it, so the cap is enforced
-   * client's module is known, so only the global cap is enforced (see
+   * across all forked children; the parent reclaims the slot on SIGCHLD. */
-   * transport_tcp.c and the Daemon Mode notes in RSYNC_COMPAT.md). */
   int max_connections;
   char** hosts_allow; /* `hosts allow = a,b`; host access allow patterns */
   int hosts_allow_count;
@@ -67,14 +66,25 @@ typedef struct DaemonModule {
 /* Global (pre-module) scalar keys.  `motd file` is parsed and stored but has
  * no wire effect yet (MOTD display is Wave C). */
 typedef struct DaemonConfGlobals {
-  int port;                  /* `port`, default DAEMON_CONF_DEFAULT_PORT (873) */
+  int port;                      /* `port`, default DAEMON_CONF_DEFAULT_PORT (873) */
-  char* motd_file;           /* `motd file`, may be NULL */
+  char* motd_file;               /* `motd file`, may be NULL */
-  char* address;             /* `address` (optional bind address), may be NULL */
+  char* address;                 /* `address` (optional bind address), may be NULL */
-  int max_connections;       /* `max connections`, default
+  int max_connections;           /* `max connections`, default
-                                DAEMON_CONF_DEFAULT_MAX_CONNECTIONS (100) */
+                                    DAEMON_CONF_DEFAULT_MAX_CONNECTIONS (100) */
-  int auth_failure_delay_ms; /* `auth failure delay`, milliseconds; default
+  int auth_failure_delay_ms;     /* `auth failure delay`, milliseconds; default
-                                DAEMON_CONF_DEFAULT_AUTH_FAILURE_DELAY_MS */
+                                    DAEMON_CONF_DEFAULT_AUTH_FAILURE_DELAY_MS */
-  char** hosts_allow;        /* `hosts allow`; global host access allow patterns */
+  int max_connections_per_host;  /* `max connections per host`, concurrent cap per
+                                    source IP; default
+                                    DAEMON_CONF_DEFAULT_MAX_CONNECTIONS_PER_HOST (0 =
+                                    unlimited) */
+  int auth_lockout_threshold;    /* `auth lockout threshold`, failed attempts from
+                                    one source before lockout; default
+                                    DAEMON_CONF_DEFAULT_AUTH_LOCKOUT_THRESHOLD (0
+                                    disables) */
+  int auth_lockout_duration_sec; /* `auth lockout duration`, seconds; default
+                                    DAEMON_CONF_DEFAULT_AUTH_LOCKOUT_DURATION_SEC
+                                    (0 disables) */
+  char** hosts_allow;            /* `hosts allow`; global host access allow patterns */
   int hosts_allow_count;
   char** hosts_deny; /* `hosts deny`; global host access deny patterns */
   int hosts_deny_count;
@@ -92,11 +102,26 @@ typedef struct DaemonConf {
 #define DAEMON_CONF_DEFAULT_MAX_CONNECTIONS 100
 /* Default `auth failure delay` in milliseconds (0 disables the throttle). */
 #define DAEMON_CONF_DEFAULT_AUTH_FAILURE_DELAY_MS 500
+/* Default `max connections per host` (0 = unlimited). */
+#define DAEMON_CONF_DEFAULT_MAX_CONNECTIONS_PER_HOST 0
+/* Default cross-process auth lockout: 10 failed attempts from one source lock
+ * it out for 300 s (0 disables either knob). */
+#define DAEMON_CONF_DEFAULT_AUTH_LOCKOUT_THRESHOLD 10
+#define DAEMON_CONF_DEFAULT_AUTH_LOCKOUT_DURATION_SEC 300
+/* Upper bound on a `max connections per host` or `auth lockout threshold`
+ * value, so a typo cannot size the shared registry absurdly. */
+#define DAEMON_CONF_MAX_CONCURRENCY_LIMIT 1000000
+/* Upper bound on `auth lockout duration` (7 days). */
+#define DAEMON_CONF_MAX_AUTH_LOCKOUT_DURATION_SEC 604800
 /* Largest accepted `auth failure delay`, so a typo cannot pin a connection
  * child in nanosleep for an absurd time. */
 /* Bounded well below the socket I/O timeout so a failed-auth child cannot hold
  * a connection slot for long enough to amplify connection-cap exhaustion. */
 #define DAEMON_CONF_MAX_AUTH_FAILURE_DELAY_MS 5000
+/* Upper bound on the number of [module] sections, so the shared registry's
+ * per-module counter array stays fixed-size.  The parser rejects the next
+ * section past this bound. */
+#define DAEMON_CONF_MAX_MODULES 256
 /* Longest accepted config line (excluding the trailing newline).  Longer lines
  * are rejected rather than buffered unboundedly. */
 #define DAEMON_CONF_MAX_LINE 4096
@@ -129,8 +154,9 @@ bool daemon_module_name_valid(const char* name);
 /* Parse one --dparam=KEY=VALUE (or "--dparam KEY=VALUE") override string and
  * apply it to the global keys only.  Keys are case-insensitive and limited to
  * the global keys defined by the grammar (port, motd file, address,
- * max connections, auth failure delay, hosts allow, hosts deny).  Returns 0 on
+ * max connections, max connections per host, auth failure delay,
- * success, -1 on error (err filled). */
+ * auth lockout threshold, auth lockout duration, hosts allow, hosts deny).
+ * Returns 0 on success, -1 on error (err filled). */
 int daemon_conf_apply_dparam(DaemonConf* conf, const char* assignment, char* err, size_t err_size);
 
 /* Host access-control matching (pure; no I/O).  `daemon_host_pattern_match`

src/shared/daemon_limits.c

@@ -0,0 +1,494 @@
+#include "daemon_limits.h"
+#include "daemon_conf.h"
+#include "log.h"
+#include <arpa/inet.h>
+#include <netinet/in.h>
+#include <stdatomic.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/mman.h>
+#include <time.h>
+
+/* The two module-count bounds must agree: the daemon config parser never
+ * produces more than DAEMON_CONF_MAX_MODULES modules, so the shared registry's
+ * per-module counter array is sized from the same bound. */
+_Static_assert(DAEMON_LIMITS_MAX_MODULES == DAEMON_CONF_MAX_MODULES,
+               "daemon_limits module bound must match daemon_conf");
+
+/* Slot lifecycle states (stored in slot_state). */
+enum {
+  SLOT_FREE = 0,
+  SLOT_CLAIMED = 1,
+  SLOT_REGISTERED = 2,
+};
+
+/* The registry header lives at the base of the shared mapping; the pointer
+ * fields point at the arrays carved out of the same mapping.  Absolute pointers
+ * remain valid in a forked child because fork() clones the address space and
+ * mapping, so parent and child observe the same virtual addresses. */
+struct DaemonLimitRegistry {
+  int max_slots;
+  int module_count;
+  int host_slots; /* power of two; 1 when no per-source tracking is needed */
+  int per_host_cap;
+  int lockout_threshold;
+  int lockout_duration_sec;
+  size_t map_size;
+  _Atomic long long host_full_warn; /* last "table full" warning epoch */
+  _Atomic int* slot_state;
+  _Atomic int* slot_pid;
+  _Atomic int* slot_module;
+  _Atomic int* slot_host; /* per-source table bucket, or -1 */
+  _Atomic int* module_active;
+  _Atomic uint64_t* host_key; /* 0 == empty bucket */
+  _Atomic int* host_active;
+  _Atomic int* host_fail;
+  _Atomic long long* host_until;    /* epoch seconds the lockout expires */
+  _Atomic long long* host_last_use; /* epoch seconds the bucket was last touched */
+};
+
+static size_t round_up(size_t n, size_t align) {
+  return (n + align - 1) & ~(align - 1);
+}
+
+static size_t next_pow2(size_t n) {
+  size_t p = 1;
+  while (p < n)
+    p <<= 1;
+  return p;
+}
+
+/* Parse a numeric IPv4/IPv6 peer string into family + raw bytes. */
+static bool parse_peer_ip(const char* peer_ip, int* family, unsigned char* bytes) {
+  if (!peer_ip || *peer_ip == '\0')
+    return false;
+  struct in_addr v4;
+  if (inet_pton(AF_INET, peer_ip, &v4) == 1) {
+    memcpy(bytes, &v4, sizeof(v4));
+    *family = AF_INET;
+    return true;
+  }
+  struct in6_addr v6;
+  if (inet_pton(AF_INET6, peer_ip, &v6) == 1) {
+    memcpy(bytes, &v6, sizeof(v6));
+    *family = AF_INET6;
+    return true;
+  }
+  return false;
+}
+
+uint64_t daemon_limits_host_hash(const char* peer_ip, bool* ok) {
+  if (ok)
+    *ok = false;
+  unsigned char bytes[16];
+  int family = AF_UNSPEC;
+  if (!parse_peer_ip(peer_ip, &family, bytes))
+    return 0;
+  uint64_t hash = 14695981039346656037ULL ^ (uint64_t)(uint32_t)family;
+  size_t length = family == AF_INET ? 4 : 16;
+  for (size_t i = 0; i < length; i++) {
+    hash ^= bytes[i];
+    hash *= 1099511628211ULL;
+  }
+  if (hash == 0)
+    hash = 0x9e3779b97f4a7c15ULL;
+  if (ok)
+    *ok = true;
+  return hash;
+}
+
+/* True when the registry must maintain per-source buckets: either the per-host
+ * cap is configured, or the auth lockout is (threshold AND duration > 0).  A
+ * lockout threshold without a duration is a no-op, so it must not size or intern
+ * the table.  create(), register() and the lockout paths all agree on this. */
+static bool registry_tracks_hosts(const DaemonLimitRegistry* registry) {
+  return registry->per_host_cap > 0 ||
+         (registry->lockout_threshold > 0 && registry->lockout_duration_sec > 0);
+}
+
+/* Find the bucket holding `peer_ip`, or -1 when it has no entry.  Finding a
+ * bucket refreshes its last-use time so the eviction policy sees it as live. */
+static int host_lookup(DaemonLimitRegistry* registry, const char* peer_ip) {
+  bool ok = false;
+  uint64_t key = daemon_limits_host_hash(peer_ip, &ok);
+  if (!ok)
+    return -1;
+  size_t mask = (size_t)registry->host_slots - 1;
+  size_t start = (size_t)(key & mask);
+  for (size_t i = 0; i < (size_t)registry->host_slots; i++) {
+    size_t idx = (start + i) & mask;
+    uint64_t current = atomic_load_explicit(&registry->host_key[idx], memory_order_acquire);
+    if (current == key) {
+      atomic_store_explicit(&registry->host_last_use[idx], (long long)time(NULL),
+                            memory_order_relaxed);
+      return (int)idx;
+    }
+    if (current == 0)
+      return -1; /* no tombstones: an empty bucket ends the probe chain */
+  }
+  return -1;
+}
+
+/* A bucket with no live connection may be repurposed: immediately when its
+ * lockout deadline has already passed (the review's "expired" case), or after an
+ * idle window when it holds no pending lockout.  A bucket with a future lockout
+ * deadline is retained so the lockout actually lasts its configured duration. */
+static bool host_bucket_reclaimable(DaemonLimitRegistry* registry, size_t idx, long long now) {
+  if (atomic_load_explicit(&registry->host_active[idx], memory_order_relaxed) != 0)
+    return false;
+  long long until = atomic_load_explicit(&registry->host_until[idx], memory_order_relaxed);
+  if (until != 0)
+    return until <= now;
+  long long last_use = atomic_load_explicit(&registry->host_last_use[idx], memory_order_relaxed);
+  /* A bucket whose key is published but whose last_use has not yet been stamped
+   * (last_use == 0) must be treated as live: reclaiming it here would steal a
+   * bucket a racing child just claimed.  The claim path also stamps last_use
+   * before publishing the key, so this window cannot persist. */
+  return last_use != 0 && now - last_use >= DAEMON_LIMITS_HOST_EVICT_IDLE_SEC;
+}
+
+/* Emit at most one "per-source table full" warning per
+ * DAEMON_LIMITS_HOST_FULL_WARN_SEC across all forked children.  Called from a
+ * normal (non-signal) child path, so logging is safe here. */
+static void host_warn_table_full(DaemonLimitRegistry* registry, long long now) {
+  long long last = atomic_load_explicit(&registry->host_full_warn, memory_order_relaxed);
+  if (last != 0 && now - last < DAEMON_LIMITS_HOST_FULL_WARN_SEC)
+    return;
+  if (atomic_compare_exchange_strong_explicit(&registry->host_full_warn, &last, now,
+                                              memory_order_relaxed, memory_order_relaxed)) {
+    log_message(LOG_LEVEL_WARNING,
+                "daemon: per-source registry is full (%d slots) and no bucket can be reclaimed; "
+                "'max connections per host' and the auth lockout are temporarily not enforced for "
+                "new sources (the per-module cap and host ACLs still apply)",
+                registry->host_slots);
+  }
+}
+
+/* Find or insert the bucket for `peer_ip`.  Insertion is a lock-free CAS so two
+ * forked children racing on the same source converge on one bucket.
+ *
+ * When the probe finds no empty bucket it reclaims, via a key CAS, the first
+ * bucket that is reclaimable (expired lockout or idle, and no active
+ * connection) and resets its counters.  This bounds the table's lifetime so it
+ * cannot fill permanently and stay fail-open.  Returns -1 only when the address
+ * is unparseable or the table is genuinely full of live/locked buckets
+ * (callers fail open: the global/module caps and ACLs still apply). */
+static int host_intern(DaemonLimitRegistry* registry, const char* peer_ip) {
+  bool ok = false;
+  uint64_t key = daemon_limits_host_hash(peer_ip, &ok);
+  if (!ok)
+    return -1;
+  long long now = (long long)time(NULL);
+  size_t mask = (size_t)registry->host_slots - 1;
+  size_t start = (size_t)(key & mask);
+  /* A couple of passes bound the work: the first normally claims/seeds a bucket;
+   * a lost eviction CAS retries once against the freshly observed table. */
+  for (int pass = 0; pass < 2; pass++) {
+    int evict = -1;
+    uint64_t evict_key = 0;
+    for (size_t i = 0; i < (size_t)registry->host_slots; i++) {
+      size_t idx = (start + i) & mask;
+      uint64_t current = atomic_load_explicit(&registry->host_key[idx], memory_order_acquire);
+      if (current == key) {
+        atomic_store_explicit(&registry->host_last_use[idx], now, memory_order_relaxed);
+        return (int)idx;
+      }
+      if (current == 0) {
+        /* Stamp last_use *before* publishing the key so a reclaimer racing the
+         * claim can never observe a claimed bucket with last_use == 0 and
+         * evict it.  A pre-stamp is harmless if the CAS loses: the bucket is
+         * either still empty (never inspected for reclaim) or has just been
+         * taken by another source that wants a fresh timestamp anyway. */
+        atomic_store_explicit(&registry->host_last_use[idx], now, memory_order_relaxed);
+        uint64_t expected = 0;
+        if (atomic_compare_exchange_strong_explicit(&registry->host_key[idx], &expected, key,
+                                                    memory_order_acq_rel, memory_order_acquire)) {
+          return (int)idx;
+        }
+        if (atomic_load_explicit(&registry->host_key[idx], memory_order_acquire) == key) {
+          return (int)idx;
+        }
+        continue; /* another child won this empty bucket; keep probing */
+      }
+      if (evict < 0 && host_bucket_reclaimable(registry, idx, now)) {
+        evict = (int)idx;
+        evict_key = current;
+      }
+    }
+    if (evict >= 0) {
+      /* Refresh the timestamp before the key changes hands so the reused bucket
+       * is not seen as immediately idle by a racing reclaimer. */
+      atomic_store_explicit(&registry->host_last_use[evict], now, memory_order_relaxed);
+      uint64_t expected = evict_key;
+      if (atomic_compare_exchange_strong_explicit(&registry->host_key[evict], &expected, key,
+                                                  memory_order_acq_rel, memory_order_acquire)) {
+        /* The bucket now belongs to the new source; clear the evicted source's
+         * stale lockout/failure state. */
+        atomic_store_explicit(&registry->host_active[evict], 0, memory_order_relaxed);
+        atomic_store_explicit(&registry->host_fail[evict], 0, memory_order_relaxed);
+        atomic_store_explicit(&registry->host_until[evict], 0, memory_order_relaxed);
+        /* Two children can race to intern the same brand-new key into different
+         * eviction targets, leaving the table with duplicate buckets for `key`.
+         * Re-scan for the first (canonical) bucket holding `key`; when it
+         * precedes `evict`, drop our duplicate's occupancy and hand back the
+         * canonical bucket so per-source counts are not orphaned on the
+         * duplicate.  The duplicate keeps its key, so no tombstone hole is
+         * created and probe chains stay intact; it ages out normally. */
+        for (size_t i = 0; i < (size_t)registry->host_slots; i++) {
+          size_t candidate = (start + i) & mask;
+          uint64_t found =
+              atomic_load_explicit(&registry->host_key[candidate], memory_order_acquire);
+          if (found == key) {
+            if (candidate != (size_t)evict) {
+              atomic_store_explicit(&registry->host_active[evict], 0, memory_order_relaxed);
+              return (int)candidate;
+            }
+            break;
+          }
+          if (found == 0)
+            break; /* the key is present at `evict`, so this cannot happen first */
+        }
+        return evict;
+      }
+      continue; /* lost the race; re-probe with fresh observations */
+    }
+    break; /* no free and no reclaimable bucket: genuinely full */
+  }
+  host_warn_table_full(registry, now);
+  return -1;
+}
+
+DaemonLimitRegistry* daemon_limits_create(int max_slots, int module_count, int per_host_cap,
+                                          int lockout_threshold, int lockout_duration_sec) {
+  if (max_slots < DAEMON_LIMITS_MIN_SLOTS)
+    max_slots = DAEMON_LIMITS_MIN_SLOTS;
+  if (max_slots > DAEMON_LIMITS_MAX_SLOTS)
+    max_slots = DAEMON_LIMITS_MAX_SLOTS;
+  if (module_count < 1)
+    module_count = 1;
+  if (module_count > DAEMON_LIMITS_MAX_MODULES)
+    module_count = DAEMON_LIMITS_MAX_MODULES;
+  if (per_host_cap < 0)
+    per_host_cap = 0;
+  if (lockout_threshold < 0)
+    lockout_threshold = 0;
+  if (lockout_duration_sec < 0)
+    lockout_duration_sec = 0;
+
+  bool need_hosts = per_host_cap > 0 || (lockout_threshold > 0 && lockout_duration_sec > 0);
+  int host_slots = 1;
+  if (need_hosts) {
+    size_t want = (size_t)max_slots * 4;
+    if (want < 64)
+      want = 64;
+    if (want > DAEMON_LIMITS_MAX_HOST_SLOTS)
+      want = DAEMON_LIMITS_MAX_HOST_SLOTS;
+    host_slots = (int)next_pow2(want);
+  }
+
+  size_t header = round_up(sizeof(DaemonLimitRegistry), 16);
+  size_t slot_bytes =
+      round_up((size_t)max_slots * sizeof(_Atomic int), 16) * 4; /* state,pid,module,host */
+  size_t module_bytes = round_up((size_t)module_count * sizeof(_Atomic int), 16);
+  size_t host_key_bytes = round_up((size_t)host_slots * sizeof(_Atomic uint64_t), 16);
+  size_t host_int_bytes = round_up((size_t)host_slots * sizeof(_Atomic int), 16) * 2;
+  size_t host_until_bytes = round_up((size_t)host_slots * sizeof(_Atomic long long), 16) * 2;
+  size_t total =
+      header + slot_bytes + module_bytes + host_key_bytes + host_int_bytes + host_until_bytes + 16;
+
+  void* map = mmap(NULL, total, PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS, -1, 0);
+  if (map == MAP_FAILED)
+    return NULL;
+  memset(map, 0, total);
+
+  DaemonLimitRegistry* registry = (DaemonLimitRegistry*)map;
+  registry->max_slots = max_slots;
+  registry->module_count = module_count;
+  registry->host_slots = host_slots;
+  registry->per_host_cap = per_host_cap;
+  registry->lockout_threshold = lockout_threshold;
+  registry->lockout_duration_sec = lockout_duration_sec;
+  registry->map_size = total;
+
+  unsigned char* cursor = (unsigned char*)map + header;
+  registry->slot_state = (atomic_int*)cursor;
+  cursor += (size_t)max_slots * sizeof(_Atomic int);
+  registry->slot_pid = (atomic_int*)cursor;
+  cursor += (size_t)max_slots * sizeof(_Atomic int);
+  registry->slot_module = (atomic_int*)cursor;
+  cursor += (size_t)max_slots * sizeof(_Atomic int);
+  registry->slot_host = (atomic_int*)cursor;
+  cursor += (size_t)max_slots * sizeof(_Atomic int);
+  registry->module_active = (atomic_int*)cursor;
+  cursor += (size_t)module_count * sizeof(_Atomic int);
+  cursor = (unsigned char*)round_up((size_t)(uintptr_t)cursor, 16);
+  registry->host_key = (_Atomic uint64_t*)cursor;
+  cursor += (size_t)host_slots * sizeof(_Atomic uint64_t);
+  registry->host_active = (atomic_int*)cursor;
+  cursor += (size_t)host_slots * sizeof(_Atomic int);
+  registry->host_fail = (atomic_int*)cursor;
+  cursor += (size_t)host_slots * sizeof(_Atomic int);
+  cursor = (unsigned char*)round_up((size_t)(uintptr_t)cursor, 16);
+  registry->host_until = (atomic_llong*)cursor;
+  cursor += (size_t)host_slots * sizeof(_Atomic long long);
+  registry->host_last_use = (atomic_llong*)cursor;
+
+  for (int i = 0; i < max_slots; i++) {
+    atomic_store(&registry->slot_module[i], -1);
+    atomic_store(&registry->slot_host[i], -1);
+  }
+  return registry;
+}
+
+void daemon_limits_destroy(DaemonLimitRegistry* registry) {
+  if (!registry)
+    return;
+  munmap(registry, registry->map_size);
+}
+
+int daemon_limits_claim_slot(DaemonLimitRegistry* registry) {
+  if (!registry)
+    return DAEMON_LIMITS_NO_SLOT;
+  for (int i = 0; i < registry->max_slots; i++) {
+    int expected = SLOT_FREE;
+    if (atomic_compare_exchange_strong(&registry->slot_state[i], &expected, SLOT_CLAIMED)) {
+      atomic_store(&registry->slot_pid[i], 0);
+      atomic_store(&registry->slot_module[i], -1);
+      atomic_store(&registry->slot_host[i], -1);
+      return i;
+    }
+  }
+  return DAEMON_LIMITS_NO_SLOT;
+}
+
+void daemon_limits_set_slot_pid(DaemonLimitRegistry* registry, int slot, long pid) {
+  if (!registry || slot < 0 || slot >= registry->max_slots)
+    return;
+  atomic_store(&registry->slot_pid[slot], (int)pid);
+}
+
+void daemon_limits_reclaim_slot(DaemonLimitRegistry* registry, int slot) {
+  if (!registry || slot < 0 || slot >= registry->max_slots)
+    return;
+  atomic_exchange_explicit(&registry->slot_state[slot], SLOT_FREE, memory_order_acq_rel);
+  atomic_store_explicit(&registry->slot_pid[slot], 0, memory_order_relaxed);
+  /* The module/host occupancy arrays are derived from the slot table; do not
+   * decrement here or a SIGKILL between a child's increment and its REGISTERED
+   * publish would leak a count.  Callers that need the derived counts call
+   * daemon_limits_recompute. */
+}
+
+void daemon_limits_reclaim_pid(DaemonLimitRegistry* registry, long pid) {
+  if (!registry || pid <= 0)
+    return;
+  for (int i = 0; i < registry->max_slots; i++) {
+    if (atomic_load(&registry->slot_state[i]) == SLOT_FREE)
+      continue;
+    if (atomic_load(&registry->slot_pid[i]) == (int)pid) {
+      daemon_limits_reclaim_slot(registry, i);
+      return;
+    }
+  }
+}
+
+void daemon_limits_recompute(DaemonLimitRegistry* registry) {
+  if (!registry)
+    return;
+  /* Zero the derived arrays, then re-derive solely from the REGISTERED slots.
+   * A child that was SIGKILLed after incrementing a counter but before
+   * publishing REGISTERED is not counted, and its leaked increment is erased by
+   * the zeroing, so the leak cannot persist. */
+  for (int m = 0; m < registry->module_count; m++)
+    atomic_store_explicit(&registry->module_active[m], 0, memory_order_relaxed);
+  for (int h = 0; h < registry->host_slots; h++)
+    atomic_store_explicit(&registry->host_active[h], 0, memory_order_relaxed);
+  for (int i = 0; i < registry->max_slots; i++) {
+    if (atomic_load_explicit(&registry->slot_state[i], memory_order_acquire) != SLOT_REGISTERED)
+      continue;
+    int module = atomic_load_explicit(&registry->slot_module[i], memory_order_relaxed);
+    if (module >= 0 && module < registry->module_count)
+      atomic_fetch_add_explicit(&registry->module_active[module], 1, memory_order_relaxed);
+    int host = atomic_load_explicit(&registry->slot_host[i], memory_order_relaxed);
+    if (host >= 0 && host < registry->host_slots)
+      atomic_fetch_add_explicit(&registry->host_active[host], 1, memory_order_relaxed);
+  }
+}
+
+DaemonLimitResult daemon_limits_register(DaemonLimitRegistry* registry, int slot, int module_index,
+                                         const char* peer_ip, int module_cap) {
+  if (!registry || slot < 0 || slot >= registry->max_slots)
+    return DAEMON_LIMIT_UNAVAILABLE;
+  if (module_index < 0 || module_index >= registry->module_count)
+    return DAEMON_LIMIT_UNAVAILABLE;
+  if (atomic_load_explicit(&registry->slot_state[slot], memory_order_acquire) != SLOT_CLAIMED)
+    return DAEMON_LIMIT_UNAVAILABLE;
+
+  int host = -1;
+  if (registry_tracks_hosts(registry))
+    host = host_intern(registry, peer_ip);
+
+  int module_count = atomic_fetch_add(&registry->module_active[module_index], 1) + 1;
+  if (module_cap > 0 && module_count > module_cap) {
+    atomic_fetch_sub(&registry->module_active[module_index], 1);
+    return DAEMON_LIMIT_MODULE_FULL;
+  }
+  if (host >= 0) {
+    int host_count = atomic_fetch_add(&registry->host_active[host], 1) + 1;
+    if (registry->per_host_cap > 0 && host_count > registry->per_host_cap) {
+      atomic_fetch_sub(&registry->host_active[host], 1);
+      atomic_fetch_sub(&registry->module_active[module_index], 1);
+      return DAEMON_LIMIT_HOST_FULL;
+    }
+  }
+  atomic_store(&registry->slot_module[slot], module_index);
+  atomic_store(&registry->slot_host[slot], host);
+  atomic_store_explicit(&registry->slot_state[slot], SLOT_REGISTERED, memory_order_release);
+  return DAEMON_LIMIT_OK;
+}
+
+bool daemon_limits_auth_locked(DaemonLimitRegistry* registry, const char* peer_ip,
+                               int* seconds_remaining) {
+  if (!registry || registry->lockout_threshold <= 0 || registry->lockout_duration_sec <= 0)
+    return false;
+  int bucket = host_lookup(registry, peer_ip);
+  if (bucket < 0)
+    return false;
+  long long until = atomic_load(&registry->host_until[bucket]);
+  long long now = (long long)time(NULL);
+  if (until > now) {
+    if (seconds_remaining)
+      *seconds_remaining = (int)(until - now);
+    return true;
+  }
+  if (until != 0) {
+    /* The previous lockout has expired: clear the stale counter so the source
+     * gets a fresh allowance. */
+    atomic_store(&registry->host_fail[bucket], 0);
+    atomic_store(&registry->host_until[bucket], 0);
+  }
+  return false;
+}
+
+void daemon_limits_auth_record_failure(DaemonLimitRegistry* registry, const char* peer_ip) {
+  if (!registry || registry->lockout_threshold <= 0 || registry->lockout_duration_sec <= 0)
+    return;
+  int bucket = host_intern(registry, peer_ip);
+  if (bucket < 0)
+    return;
+  int failures = atomic_fetch_add(&registry->host_fail[bucket], 1) + 1;
+  if (failures >= registry->lockout_threshold) {
+    long long now = (long long)time(NULL);
+    atomic_store(&registry->host_until[bucket], now + (long long)registry->lockout_duration_sec);
+  }
+}
+
+void daemon_limits_auth_record_success(DaemonLimitRegistry* registry, const char* peer_ip) {
+  if (!registry)
+    return;
+  int bucket = host_lookup(registry, peer_ip);
+  if (bucket < 0)
+    return;
+  atomic_store(&registry->host_fail[bucket], 0);
+  atomic_store(&registry->host_until[bucket], 0);
+}

src/shared/daemon_limits.h

@@ -0,0 +1,147 @@
+#ifndef DAEMON_LIMITS_H
+#define DAEMON_LIMITS_H
+
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+
+/* Cross-process daemon connection registry.
+ *
+ * The daemon listener forks ONE child per accepted connection, so any
+ * per-module / per-source accounting must live in state shared across the
+ * forked children.  This module owns a fixed-size registry carved out of an
+ * anonymous shared mapping (mmap(MAP_SHARED | MAP_ANONYMOUS)) created by the
+ * accept-loop PARENT before it forks; every child inherits the mapping (and the
+ * pointer to it) across fork().
+ *
+ * Rules:
+ *  - ONLY C11 atomics (atomic_*); never mtx_t/pthread locks, which can deadlock
+ *    in a forked child if another thread held them at fork time.
+ *  - No heap allocation after fork: the mapping is fixed-size and all access is
+ *    atomic load/store/CAS over preallocated arrays.
+ *
+ * Slot lifecycle (the parent reclaims even when a child is SIGKILLed):
+ *   FREE --(parent claim_slot)--> CLAIMED
+ *   CLAIMED --(child register)--> REGISTERED
+ *   any --(parent reclaim)--> FREE
+ * The child records its module index and per-source bucket into the slot before
+ * publishing REGISTERED; the parent's SIGCHLD handler matches the reaped pid to
+ * the slot and, when REGISTERED, decrements the module/per-source counters.
+ * A child killed before registering holds no counts, so reclaiming a CLAIMED
+ * slot only frees the slot.
+ *
+ * Per-source identity is the normalized numeric peer IP (IPv4-mapped IPv6 is
+ * already collapsed to IPv4 by utils_fd_peer_ip); it is interned into an
+ * open-addressed, linear-probing table keyed by a 64-bit hash.  The same table
+ * also carries the cross-process auth-failure counter and lockout deadline.
+ *
+ * Per-source table lifetime: a bucket's key is never cleared back to empty (that
+ * would break every later probe chain that passed through it).  Instead the
+ * table has a bounded-lifetime eviction policy: when no empty bucket exists, the
+ * first bucket that is reclaimable -- no active connection AND (its lockout
+ * deadline has passed OR it has been idle for
+ * DAEMON_LIMITS_HOST_EVICT_IDLE_SEC) -- is atomically repurposed for the new
+ * source via a CAS of its key, and its counters are reset.  The table therefore
+ * cannot fill permanently, and a full table degrades to fail-open for the
+ * per-source cap/lockout of new sources (the per-module cap and host ACLs still
+ * apply) instead of staying fail-open forever.  A rate-limited warning is logged
+ * on the fail-open path.  The eviction race with a concurrent
+ * registration/reclaim on the same bucket is benign: it can at worst lose one
+ * source's counter (fail-open), never corrupt memory or the module caps.
+ */
+
+typedef struct DaemonLimitRegistry DaemonLimitRegistry;
+
+/* Result of a per-connection admission check. */
+typedef enum {
+  DAEMON_LIMIT_OK = 0,      /* admitted; slot is now REGISTERED */
+  DAEMON_LIMIT_MODULE_FULL, /* module's `max connections` cap reached */
+  DAEMON_LIMIT_HOST_FULL,   /* global `max connections per host` cap reached */
+  DAEMON_LIMIT_UNAVAILABLE, /* registry/slot unusable (caller fails open) */
+} DaemonLimitResult;
+
+/* Bounds for registry sizing.  A slot is one concurrently live child. */
+#define DAEMON_LIMITS_MIN_SLOTS 16
+#define DAEMON_LIMITS_MAX_SLOTS 65536
+#define DAEMON_LIMITS_MAX_HOST_SLOTS 65536
+#define DAEMON_LIMITS_NO_SLOT (-1)
+/* Upper bound on `module_count`, matching daemon_conf.h's DAEMON_CONF_MAX_MODULES
+ * (asserted in daemon_limits.c) so a caller can never size the per-module counter
+ * array larger than the config parser can produce. */
+#define DAEMON_LIMITS_MAX_MODULES 256
+
+/* Per-source table lifetime: a bucket with no active connection and no pending
+ * lockout is reclaimable once it has been idle this long, so a flood of distinct
+ * sources cannot pin the table full forever.  A bucket whose lockout deadline
+ * has passed is reclaimable immediately (independent of this idle window). */
+#define DAEMON_LIMITS_HOST_EVICT_IDLE_SEC 300
+/* Minimum spacing between "per-source table is full" warnings, so a table-full
+ * attack cannot flood the log. */
+#define DAEMON_LIMITS_HOST_FULL_WARN_SEC 60
+
+/* Create the shared registry in the calling (parent) process.  `max_slots` is
+ * the number of concurrently live children to track (clamped to
+ * [DAEMON_LIMITS_MIN_SLOTS, DAEMON_LIMITS_MAX_SLOTS]); `module_count` is the
+ * number of daemon modules (clamped to
+ * [1, DAEMON_LIMITS_MAX_MODULES]); `per_host_cap` and the lockout pair come
+ * from the daemon config (0 disables).  Returns NULL on failure (e.g. mmap
+ * allocation); callers must degrade gracefully (global cap + ACLs still
+ * apply). */
+DaemonLimitRegistry* daemon_limits_create(int max_slots, int module_count, int per_host_cap,
+                                          int lockout_threshold, int lockout_duration_sec);
+
+/* Unmap the registry.  Only the creating process may call this. */
+void daemon_limits_destroy(DaemonLimitRegistry* registry);
+
+/* Parent side: reserve a slot for the next fork.  Returns the slot index or
+ * DAEMON_LIMITS_NO_SLOT when every slot is in use. */
+int daemon_limits_claim_slot(DaemonLimitRegistry* registry);
+/* Parent side: record the forked child's pid in a claimed slot. */
+void daemon_limits_set_slot_pid(DaemonLimitRegistry* registry, int slot, long pid);
+/* Parent side: release a slot.  The slot becomes FREE; the module/per-source
+ * occupancy arrays are DERIVED state and are only refreshed by
+ * daemon_limits_recompute, which callers must invoke afterwards when they rely
+ * on the derived counts (the SIGCHLD handler batches one recompute for the whole
+ * reap).  Idempotent. */
+void daemon_limits_reclaim_slot(DaemonLimitRegistry* registry, int slot);
+/* Parent SIGCHLD side: release the slot owned by `pid` (no-op when not found).
+ * Like reclaim_slot this does not touch the derived occupancy arrays; call
+ * daemon_limits_recompute after a batch of releases. */
+void daemon_limits_reclaim_pid(DaemonLimitRegistry* registry, long pid);
+
+/* Parent side (async-signal-safe; atomics only, no malloc/log): rebuild
+ * module_active[] / host_active[] from scratch by scanning the REGISTERED slots.
+ * The slot table is the single source of truth, so this self-heals any
+ * count leaked by a child that was SIGKILLed mid-registration (it zeroes the
+ * arrays and re-derives them).  Bounded by max_slots + host_slots.  A
+ * registration racing this call can be transiently undercounted until the next
+ * recompute, which can only relax a cap briefly -- never corrupt memory. */
+void daemon_limits_recompute(DaemonLimitRegistry* registry);
+
+/* Child side: admit the connection for `module_index` from `peer_ip`.  Always
+ * tracks the module/per-source occupancy (so the parent's reclaim is
+ * symmetric); when `module_cap` > 0 it additionally enforces the per-module
+ * cap.  A NULL/empty or non-numeric `peer_ip` skips the per-source track (the
+ * callers use that to exempt a trusted loopback peer from the per-host cap; the
+ * per-module cap still applies).  Returns DAEMON_LIMIT_OK and publishes the
+ * slot, or a refusal reason. */
+DaemonLimitResult daemon_limits_register(DaemonLimitRegistry* registry, int slot, int module_index,
+                                         const char* peer_ip, int module_cap);
+
+/* Child side: true when `peer_ip` is currently locked out after too many failed
+ * authentications.  `seconds_remaining` may be NULL. */
+bool daemon_limits_auth_locked(DaemonLimitRegistry* registry, const char* peer_ip,
+                               int* seconds_remaining);
+/* Child side: count one failed authentication for `peer_ip`; once the threshold
+ * is reached the source is locked out for the configured duration. */
+void daemon_limits_auth_record_failure(DaemonLimitRegistry* registry, const char* peer_ip);
+/* Child side: clear the failure counter/lockout for a source that authenticated
+ * successfully (no-op when the source has no table entry). */
+void daemon_limits_auth_record_success(DaemonLimitRegistry* registry, const char* peer_ip);
+
+/* Pure helper: 64-bit FNV-1a hash of a numeric peer IP plus its family, used to
+ * index the per-source table.  *ok is set false (and 0 returned) for a NULL or
+ * non-numeric address.  Exposed for unit testing. */
+uint64_t daemon_limits_host_hash(const char* peer_ip, bool* ok);
+
+#endif

src/shared/data.c

@@ -23,6 +23,7 @@ Data* data_create_reserve(size_t size) {
   d->data = NULL;
   d->size = size;
   d->protocol_charge = 0;
+  d->owner = NULL;
   return d;
 }
 
@@ -36,14 +37,19 @@ Data* data_create(void* data, size_t data_size) {
   new_data->data = data;
   new_data->size = data_size;
   new_data->protocol_charge = 0;
+  new_data->owner = NULL;
   return new_data;
 }
 
 void data_destroy(Data* data) {
   if (data == NULL)
     return;
-  if (data->protocol_charge != 0)
+  if (data->protocol_charge != 0) {
-    protocol_release_memory(data->protocol_charge);
+    if (data->owner != NULL)
+      protocol_release_memory_for_session(data->owner, data->protocol_charge);
+    else
+      protocol_release_memory(data->protocol_charge);
+  }
   free(data->data);
   free(data);
 }

src/shared/data.h

@@ -3,11 +3,25 @@
 
 #include <stdlib.h>
 
+/* Forward declaration for the connection budget a received Data is charged
+ * against; defined in protocol.h (which includes this header). */
+typedef struct ProtocolSession ProtocolSession;
+
 typedef struct {
   void* data;
   size_t size;
   /* Non-zero only for a buffer charged to the protocol connection budget. */
   size_t protocol_charge;
+  /* Session whose budget `protocol_charge` was reserved from.  When non-NULL,
+   * the charge is returned to this session directly, regardless of which
+   * session (if any) is bound to the destroying thread.  owner is not
+   * guaranteed to be set whenever protocol_charge is non-zero: it is NULL for
+   * uncharged Data and for Data that has no recorded owner, in which case any
+   * charge falls back to the session bound at destroy time.
+   *
+   * Lifetime contract: a Data with a non-NULL owner must not outlive that
+   * ProtocolSession -- data_destroy dereferences owner to return the charge. */
+  ProtocolSession* owner;
 } Data;
 
 Data* data_create_empty(size_t data_size);
@@ -15,5 +29,9 @@ Data* data_create_reserve(size_t size);
 Data* data_create(void* data, size_t data_size);
 void data_destroy(Data* data);
 void protocol_release_memory(size_t charge);
+/* Release `charge` against `session` directly instead of the thread-local bound
+ * session.  Used by data_destroy to honor Data.owner; `session` must outlive
+ * the Data whose charge is being returned.  A NULL session is a no-op. */
+void protocol_release_memory_for_session(ProtocolSession* session, size_t charge);
 
 #endif

src/shared/file.c

@@ -284,23 +284,6 @@ size_t file_content_to_buffer(File* file) {
 
 /* ---- Secure filesystem primitives ---- */
 
-static int authorized_root_fd = -1;
-static char* authorized_root_path;
-
-bool file_set_authorized_root(int fd, const char* canonical_path) {
-  char* path_copy = canonical_path ? str_dup(canonical_path) : NULL;
-  if (canonical_path && !path_copy) {
-    authorized_root_fd = -1;
-    free(authorized_root_path);
-    authorized_root_path = NULL;
-    return false;
-  }
-  authorized_root_fd = fd;
-  free(authorized_root_path);
-  authorized_root_path = path_copy;
-  return true;
-}
-
 bool file_path_exists_secure(const char* path) {
   if (!path)
     return false;
@@ -483,7 +466,10 @@ static int open_dir_beneath_root(const char* resolved, const char* root) {
     rel++;
   if (*rel == '\0')
     return -1;
-  int fd = dup(authorized_root_fd);
+  int root_fd = utils_get_authorized_root_fd();
+  if (root_fd < 0)
+    return -1;
+  int fd = dup(root_fd);
   if (fd < 0)
     return -1;
   char* copy = str_dup(rel);
@@ -525,20 +511,21 @@ int file_open_secure_parent(const char* path, char** leaf_out, bool create_dirs)
     return -1;
   }
   int fd;
-  if (authorized_root_fd >= 0) {
+  int root_fd = utils_get_authorized_root_fd();
-    if (!authorized_root_path || path[0] != '/' ||
+  const char* root_path = utils_get_authorized_root_path();
-        !path_is_within_root(authorized_root_path, path)) {
+  if (root_fd >= 0) {
+    if (!root_path || path[0] != '/' || !path_is_within_root(root_path, path)) {
       free(copy);
       free(leaf);
       return -1;
     }
-    fd = dup(authorized_root_fd);
+    fd = dup(root_fd);
     if (fd < 0) {
       free(copy);
       free(leaf);
       return -1;
     }
-    size_t root_len = strlen(authorized_root_path);
+    size_t root_len = strlen(root_path);
     char* relative = str_dup(path + root_len);
     if (!relative) {
       free(copy);
@@ -602,15 +589,14 @@ int file_open_secure_parent(const char* path, char** leaf_out, bool create_dirs)
          O_NOFOLLOW walk.  Only honoured when the symlink resolves to a
          directory that stays beneath the authorized root, so a malicious link
          can never redirect the write outside it. */
-      if (next < 0 && file_keep_dirlinks && authorized_root_path != NULL &&
+      if (next < 0 && file_keep_dirlinks && root_path != NULL &&
           (errno == ELOOP || errno == ENOTDIR || errno == EACCES)) {
         struct stat lst;
         if (fstatat(fd, component, &lst, AT_SYMLINK_NOFOLLOW) == 0 && S_ISLNK(lst.st_mode)) {
           char candidate[PATH_MAX];
           char root[PATH_MAX];
-          if (realpath(authorized_root_path, root) &&
+          if (realpath(root_path, root) && snprintf(candidate, sizeof(candidate), "%s%s/%s", root,
-              snprintf(candidate, sizeof(candidate), "%s%s/%s", root, rel_buf, component) <
+                                                    rel_buf, component) < (int)sizeof(candidate)) {
-                  (int)sizeof(candidate)) {
             char resolved[PATH_MAX];
             if (realpath(candidate, resolved) && strcmp(resolved, root) != 0 &&
                 strncmp(root, resolved, strlen(root)) == 0 &&
@@ -685,8 +671,9 @@ bool file_ensure_directory_secure(const char* path) {
     return false;
   /* The authorized root is already an open directory, and the filesystem root
      is always present: there is no final component left to create for them. */
+  const char* root_path = utils_get_authorized_root_path();
   bool root_is_open =
-      authorized_root_fd >= 0 && authorized_root_path && strcmp(norm, authorized_root_path) == 0;
+      utils_get_authorized_root_fd() >= 0 && root_path && strcmp(norm, root_path) == 0;
   if (root_is_open || strcmp(norm, "/") == 0) {
     free(norm);
     return true;
@@ -733,8 +720,9 @@ bool file_directory_exists_secure(const char* path) {
   char* norm = normalize_directory_path(path);
   if (!norm)
     return false;
+  const char* root_path = utils_get_authorized_root_path();
   bool root_is_open =
-      authorized_root_fd >= 0 && authorized_root_path && strcmp(norm, authorized_root_path) == 0;
+      utils_get_authorized_root_fd() >= 0 && root_path && strcmp(norm, root_path) == 0;
   if (root_is_open || strcmp(norm, "/") == 0) {
     free(norm);
     return true;

src/shared/file.h

@@ -62,9 +62,6 @@ void file_set_keep_dirlinks(bool enable);
 void file_set_trust_sender(bool enable);
 bool file_get_trust_sender(void);
 
-/* A configured fd without a canonical identity deliberately rejects paths. */
-bool file_set_authorized_root(int fd, const char* canonical_path);
-
 /* Secure path/filesystem primitives (symlink-safe, O_NOFOLLOW, root-confined). */
 bool file_path_exists_secure(const char* path);
 bool file_stat_secure(const char* path, struct stat* st);

src/shared/protocol.c

@@ -40,7 +40,9 @@ static bool protocol_reserve_memory(ProtocolSession* session, size_t charge) {
   }
 }
 
-static void protocol_release_memory_for_session(ProtocolSession* session, size_t charge) {
+void protocol_release_memory_for_session(ProtocolSession* session, size_t charge) {
+  if (!session)
+    return;
   unsigned long long allocated = atomic_load(&session->total_allocated_bytes);
   while (true) {
     unsigned long long remaining = (unsigned long long)charge >= allocated ? 0 : allocated - charge;
@@ -573,6 +575,7 @@ Data* protocol_receive_data_limited(ProtocolSession* session, unsigned long long
     return NULL;
   }
   result->protocol_charge = allocation_size;
+  result->owner = session;
   return result;
 }
 

src/shared/transport_tcp.c

@@ -1,4 +1,5 @@
 #include "transport_tcp.h"
+#include "daemon_limits.h"
 #include "log.h"
 #include "protocol.h"
 #include "utils.h"
@@ -8,6 +9,7 @@
 #include <netinet/in.h>
 #include <netinet/tcp.h>
 #include <openssl/ssl.h>
+#include <pthread.h>
 #include <signal.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -18,19 +20,45 @@
 
 static volatile sig_atomic_t g_active_connections = 0;
 
+/* Shared registry installed on the active server; the SIGCHLD handler needs a
+ * file-scope pointer so it can reclaim the dead child's slot.  Set once by
+ * accept_loop before the fork loop (single-threaded parent). */
+static DaemonLimitRegistry* g_limit_registry = NULL;
+/* Slot reserved by the parent for the connection child currently being forked.
+ * Written before fork(), read by the child (which inherits the value). */
+static int g_current_slot = DAEMON_LIMITS_NO_SLOT;
+
 static void tcp_apply_socket_timeout(int fd);
 static void tcp_enable_nodelay_default(int fd, int family);
 
 static void sigchld_handler(int sig) {
   (void)sig;
   int saved_errno = errno;
-  while (waitpid(-1, NULL, WNOHANG) > 0) {
+  pid_t pid;
+  while ((pid = waitpid(-1, NULL, WNOHANG)) > 0) {
     if (g_active_connections > 0)
       g_active_connections--;
+    daemon_limits_reclaim_pid(g_limit_registry, (long)pid);
   }
+  /* Re-derive the occupancy counters once for the whole reap batch.  The slot
+   * table is the source of truth, so this self-heals any count leaked by a child
+   * SIGKILLed mid-registration.  Atomics only: async-signal-safe. */
+  if (g_limit_registry)
+    daemon_limits_recompute(g_limit_registry);
   errno = saved_errno;
 }
 
+/* Reset a signal to its default action with sigaction (preferred over
+ * signal(3), whose semantics are implementation-defined).  Used in the forked
+ * child before it can spawn any thread. */
+static void reset_signal_default(int sig) {
+  struct sigaction action;
+  memset(&action, 0, sizeof(action));
+  action.sa_handler = SIG_DFL;
+  sigemptyset(&action.sa_mask);
+  sigaction(sig, &action, NULL);
+}
+
 /* Map a listen socket's address to its numeric port for logging, independent
  * of whether it is an IPv4 or IPv6 sockaddr. */
 static unsigned short server_address_port(const struct sockaddr_storage* addr) {
@@ -108,6 +136,7 @@ Server* server_create_ex(int port, const ServerBindOptions* bind_opts) {
   server->ssl_ctx = NULL;
   server->max_connections = 100;
   server->active_connections = 0;
+  server->limit_registry = NULL;
 
   return server;
 }
@@ -121,6 +150,15 @@ void server_set_max_connections(Server* server, unsigned int max_connections) {
     server->max_connections = max_connections;
 }
 
+void server_set_limit_registry(Server* server, struct DaemonLimitRegistry* registry) {
+  if (server)
+    server->limit_registry = registry;
+}
+
+int transport_tcp_current_slot(void) {
+  return g_current_slot;
+}
+
 void server_delete(Server** server) {
   if (server == NULL || *server == NULL)
     return;
@@ -139,7 +177,17 @@ static void accept_loop(Server* server, void (*child_fn)(int, void*), void* chil
     log_perror("Could not listen on port!");
     return;
   }
-  signal(SIGCHLD, sigchld_handler);
+  /* SIGCHLD via sigaction (not signal(3)); SA_RESTART keeps accept(2) from
+   * failing with EINTR, and SA_NOCLDSTOP only notifies on child exit.  The
+   * accept loop is single-threaded at this point, so installing here cannot race
+   * a worker thread. */
+  struct sigaction chld_action;
+  memset(&chld_action, 0, sizeof(chld_action));
+  chld_action.sa_handler = sigchld_handler;
+  sigemptyset(&chld_action.sa_mask);
+  chld_action.sa_flags = SA_RESTART | SA_NOCLDSTOP;
+  sigaction(SIGCHLD, &chld_action, NULL);
+  g_limit_registry = server->limit_registry;
   while (1) {
     struct sockaddr_storage client_addr;
     socklen_t client_len = sizeof(client_addr);
@@ -159,9 +207,37 @@ static void accept_loop(Server* server, void (*child_fn)(int, void*), void* chil
       close(fd);
       continue;
     }
+    int slot = DAEMON_LIMITS_NO_SLOT;
+    if (server->limit_registry) {
+      slot = daemon_limits_claim_slot(server->limit_registry);
+      if (slot == DAEMON_LIMITS_NO_SLOT) {
+        /* The global cap bounds live children, so this only happens when the
+         * fixed registry is smaller than the configured cap; fail closed. */
+        log_message(LOG_LEVEL_WARNING, "Connection registry slots exhausted (max %u), rejecting %s",
+                    server->max_connections, peer);
+        close(fd);
+        continue;
+      }
+    }
     log_message(LOG_LEVEL_INFO, "%s from %s", log_fmt, peer);
+    g_current_slot = slot;
+    /* Block SIGCHLD across fork() and the parent's pid publication: a child
+     * that exits immediately must not be reaped before its slot records its
+     * pid, which would leak the slot and its module/source counts.  Use
+     * pthread_sigmask rather than sigprocmask so the behavior is well defined
+     * even if this process ever gains threads: the mask is per-thread, the fork
+     * copies only the calling thread, and the child inherits this thread's
+     * blocked mask until it restores `previous` below.  No thread exists yet at
+     * this point, and none is created before the mask is restored, so the
+     * critical window is race-free. */
+    sigset_t blocked;
+    sigset_t previous;
+    sigemptyset(&blocked);
+    sigaddset(&blocked, SIGCHLD);
+    pthread_sigmask(SIG_BLOCK, &blocked, &previous);
     pid_t pid = fork();
     if (pid == 0) {
+      pthread_sigmask(SIG_SETMASK, &previous, NULL);
       /* Connection children must not run the parent's global cleanup(): it
        * frees state (credentials / daemon conf) that the child's worker
        * threads may still be reading and closes fd numbers the child could
@@ -169,15 +245,21 @@ static void accept_loop(Server* server, void (*child_fn)(int, void*), void* chil
        * terminates the child directly; SIGCHLD is reset too since a child
        * must never reap the parent's children.  This runs before the child
        * spawns any thread, so it cannot race one. */
-      signal(SIGINT, SIG_DFL);
+      reset_signal_default(SIGINT);
-      signal(SIGTERM, SIG_DFL);
+      reset_signal_default(SIGTERM);
-      signal(SIGCHLD, SIG_DFL);
+      reset_signal_default(SIGCHLD);
       close(server->file_descriptor);
       child_fn(fd, child_ctx);
       _exit(0);
     } else if (pid > 0) {
       g_active_connections++;
+      if (server->limit_registry)
+        daemon_limits_set_slot_pid(server->limit_registry, slot, (long)pid);
+    } else if (server->limit_registry) {
+      /* fork() failed: release the reservation so the slot is not leaked. */
+      daemon_limits_reclaim_slot(server->limit_registry, slot);
     }
+    pthread_sigmask(SIG_SETMASK, &previous, NULL);
     close(fd);
   }
 }

src/shared/transport_tcp.h

@@ -7,6 +7,10 @@
 #include <stdbool.h>
 #include <sys/types.h>
 
+/* Cross-process daemon registry (daemon_limits.c).  Only an opaque pointer is
+ * stored here so the transport layer does not depend on daemon config. */
+struct DaemonLimitRegistry;
+
 typedef struct Server {
   struct sockaddr_storage address;
   unsigned int address_length;
@@ -14,6 +18,7 @@ typedef struct Server {
   void* ssl_ctx;
   unsigned int max_connections;
   volatile unsigned int active_connections;
+  struct DaemonLimitRegistry* limit_registry;
 } Server;
 
 typedef struct Client {
@@ -48,6 +53,14 @@ Server* server_create(int port);
 /* Override the listener's connection cap (the global daemon `max connections`
  * value).  A non-positive value is ignored so the default cap stands. */
 void server_set_max_connections(Server* server, unsigned int max_connections);
+/* Install the shared per-module / per-source registry used by the accept loop
+ * to reserve a slot for each forked child.  NULL disables the accounting (the
+ * global cap and ACLs still apply). */
+void server_set_limit_registry(Server* server, struct DaemonLimitRegistry* registry);
+/* Slot reserved for the connection child currently running (set by the parent
+ * before fork, inherited by the child).  Returns DAEMON_LIMITS_NO_SLOT (-1)
+ * outside the accept-loop child path. */
+int transport_tcp_current_slot(void);
 bool server_listen(Server* server, void (*handler)(int file_descriptor));
 void server_accept_loop(Server* server, void (*child_fn)(int, void*), void* child_ctx,
                         const char* log_fmt);

src/shared/utils.c

@@ -36,6 +36,17 @@ void utils_set_authorized_root_fd(int fd) {
   (void)utils_set_authorized_root(fd, NULL);
 }
 
+/* Accessors for the process-global authorized root.  The path pointer is
+ * borrowed and valid until the next setter call; the root is a single-threaded,
+ * set-before-worker-threads value (see server.c), so these carry no locking. */
+int utils_get_authorized_root_fd(void) {
+  return authorized_root_fd;
+}
+
+const char* utils_get_authorized_root_path(void) {
+  return authorized_root_path;
+}
+
 bool path_is_within_root(const char* root, const char* path) {
   size_t root_len = strlen(root);
   return strncmp(root, path, root_len) == 0 && (path[root_len] == '\0' || path[root_len] == '/');
@@ -50,15 +61,16 @@ bool path_is_within_root(const char* root, const char* path) {
  * in the extra receiver policies they apply, so they are intentionally kept
  * separate.  Both rely on the shared lexical path_is_within_root check. */
 static int open_authorized_destination(const char* dest_root) {
-  if (authorized_root_fd < 0 || !authorized_root_path || !dest_root ||
+  int root_fd = utils_get_authorized_root_fd();
-      !path_is_within_root(authorized_root_path, dest_root))
+  const char* root_path = utils_get_authorized_root_path();
+  if (root_fd < 0 || !root_path || !dest_root || !path_is_within_root(root_path, dest_root))
     return -1;
 
-  int dirfd = dup(authorized_root_fd);
+  int dirfd = dup(root_fd);
   if (dirfd < 0)
     return -1;
 
-  const char* relative_path = dest_root + strlen(authorized_root_path);
+  const char* relative_path = dest_root + strlen(root_path);
   while (*relative_path == '/')
     relative_path++;
   char* relative = str_dup(*relative_path ? relative_path : ".");
@@ -689,11 +701,12 @@ DeleteWalkResult delete_extras_limited(const char* dest_root, const ArrayList* m
   if (!build_keep_index(manifest, &keep))
     return DELETE_WALK_ERROR;
   int rootfd;
-  if (authorized_root_fd >= 0) {
+  int root_fd = utils_get_authorized_root_fd();
-    if (authorized_root_path)
+  if (root_fd >= 0) {
+    if (utils_get_authorized_root_path())
       rootfd = open_authorized_destination(dest_root);
     else if (dest_root == NULL)
-      rootfd = dup(authorized_root_fd);
+      rootfd = dup(root_fd);
     else
       rootfd = -1;
   } else {

src/shared/utils.h

@@ -127,6 +127,21 @@ bool utils_set_authorized_root(int fd, const char* canonical_path);
 /* The fd-only compatibility form is fail-closed for path-based operations;
  * callers should use utils_set_authorized_root with the canonical identity. */
 void utils_set_authorized_root_fd(int fd);
+/* Read accessors for the process-wide authorized root, so every secure-walk
+ * site consumes the single shared state instead of keeping its own copy.  The
+ * fd is caller-owned (see the setters): it is returned verbatim, never dup'd,
+ * and the caller that opened it is responsible for closing it.  With no root
+ * configured the fd accessor returns -1 and the path accessor returns NULL.
+ *
+ * The pointer returned by utils_get_authorized_root_path() is borrowed into
+ * process-global state and is invalidated by the next
+ * utils_set_authorized_root() / utils_set_authorized_root_fd() call.  The fd
+ * and path are stored separately and read independently, so the pair is NOT
+ * observed atomically together; the accessors are non-reentrant and callers
+ * must serialize configuration (the server installs the root before any worker
+ * threads spawn; see utils.c). */
+int utils_get_authorized_root_fd(void);
+const char* utils_get_authorized_root_path(void);
 /* True when `path` is `root` itself or lies directly beneath it: a lexical
  * prefix test requiring the byte after `root` to be '\0' or '/'.  Both `root`
  * and `path` must be absolute canonical paths free of "."/".." components (the

tests/integration/test_daemon.py

@@ -135,7 +135,7 @@ class DaemonManager:
         self._proc = None
         self._port = None
 
-    def start(self, config_path, port_override=None, extra_args=None):
+    def start(self, config_path, port_override=None, extra_args=None, log_path=None):
         self.stop()
         # When no override is given the daemon binds the config file's `port`
         # (the plain config-port path); with an override the --dparam path.
@@ -146,7 +146,8 @@ class DaemonManager:
             cmd += ["--dparam", f"port={port_override}"]
         if extra_args:
             cmd += extra_args
-        log_path = os.path.join(TEST_DATA_DIR, "fastsyncd.log")
+        if log_path is None:
+            log_path = os.path.join(TEST_DATA_DIR, "fastsyncd.log")
         log = open(log_path, "w")
         self._proc = subprocess.Popen(
             cmd, stdout=log, stderr=log, stdin=subprocess.DEVNULL, start_new_session=True)
@@ -1208,3 +1209,80 @@ class TestDaemonTLSAuth:
             d.stop()
             os.unlink(client_creds)
             shutil.rmtree(cert_dir, ignore_errors=True)
+
+
+class TestDaemonConnectionLimits:
+    """Wave 8: cross-process per-module / per-source connection caps and the
+    shared auth lockout.  Each test boots its own daemon with a unique port so
+    the shared (per-daemon) registry state is isolated from the module-scoped
+    `daemon` fixture."""
+
+    LOCKOUT_CONF = os.path.join(TEST_DATA_DIR, "fastsyncd_lockout.conf")
+    CAPS_CONF = os.path.join(TEST_DATA_DIR, "fastsyncd_caps.conf")
+
+    @pytest.mark.ci
+    def test_auth_lockout_exempts_trusted_loopback(self):
+        """`auth lockout threshold = 1`: a trusted loopback peer is EXEMPT from
+        the shared lockout because every local client shares the 127.0.0.1
+        identity, so a single wrong password must not lock out correct-password
+        attempts (that would be a local denial of service).  The shared
+        per-source lockout machinery itself is covered by the daemon_limits unit
+        tests; this locks in the loopback policy and the absence of a stale
+        "locked out" log line."""
+        port = _find_free_port()
+        with open(self.LOCKOUT_CONF, "w") as f:
+            f.write("port = %d\n"
+                    "auth lockout threshold = 1\n"
+                    "auth lockout duration = 300\n"
+                    "\n"
+                    "[locked]\n"
+                    "path = %s\n"
+                    "auth users = alice\n"
+                    % (port, AUTH_MODULE))
+        d = DaemonManager()
+        log_path = os.path.join(TEST_DATA_DIR, f"fastsyncd_lockout_{os.getpid()}.log")
+        try:
+            d.start(self.LOCKOUT_CONF, port_override=port, extra_args=["--password-file", CRED_FILE],
+                    log_path=log_path)
+            log_before = os.path.getsize(log_path) if os.path.exists(log_path) else 0
+            # First attempt: wrong password -> a failure is logged, but a loopback
+            # peer is not counted toward the lockout.
+            wrong = _push_with_creds("127.0.0.1::locked", port, "alice", WRONG_PASS)
+            assert wrong.returncode != 0
+            # Second attempt: the correct password from the same local source must
+            # still be accepted (no lockout), which also runs the SCRAM handshake
+            # to completion in a fresh forked child.
+            right = _push_with_creds("127.0.0.1::locked", port, "alice", ALICE_PASS)
+            assert right.returncode == 0, (right.stderr or right.stdout)
+            time.sleep(0.3)
+            with open(log_path, "rb") as f:
+                f.seek(log_before)
+                tail = f.read().decode("utf-8", "replace")
+            assert "locked out" not in tail, tail[-400:]
+        finally:
+            d.stop()
+
+    def test_caps_keys_accepted_and_transfer_still_works(self):
+        """A daemon configured with the new keys (per-host cap, lockout threshold
+        and duration, per-module cap) starts and serves a normal transfer."""
+        port = _find_free_port()
+        with open(self.CAPS_CONF, "w") as f:
+            f.write("port = %d\n"
+                    "max connections per host = 5\n"
+                    "auth lockout threshold = 3\n"
+                    "auth lockout duration = 60\n"
+                    "\n"
+                    "[files]\n"
+                    "path = %s\n"
+                    "max connections = 2\n"
+                    % (port, FILES_MODULE))
+        d = DaemonManager()
+        try:
+            d.start(self.CAPS_CONF, port_override=port)
+            result = _push("127.0.0.1::files", port)
+            assert result.returncode == 0, result.stderr or result.stdout
+            received = get_dest_received_dir(FILES_MODULE, SOURCE_DIR)
+            _, missing = verify_transfer(SOURCE_DIR, received)
+            assert not missing, f"missing: {missing[:5]}"
+        finally:
+            d.stop()

tests/runner.c

@@ -9,6 +9,7 @@
 #include "test_credentials.h"
 #include "test_data.h"
 #include "test_daemon_conf.h"
+#include "test_daemon_limits.h"
 #include "test_delay_updates.h"
 #include "test_delta.h"
 #include "test_file.h"
@@ -85,6 +86,7 @@ int main() {
   RUN_TEST(test_client_cli);
   RUN_TEST(test_server);
   RUN_TEST(test_daemon_conf);
+  RUN_TEST(test_daemon_limits);
   RUN_TEST(test_motd);
   RUN_TEST(test_server_cli);
   RUN_TEST(test_fuzz_smoke);

tests/test_config.c

@@ -1,5 +1,6 @@
 #include "test_config.h"
 #include "config.h"
+#include "delta.h"
 #include "identity.h"
 #include "multiprocessing.h"
 #include "protocol.h"
@@ -2194,6 +2195,592 @@ static void test_config_receive_rejects_unified_invariants() {
   }
 }
 
+/* ---------------------------------------------------------------------------
+ * Wire round-trip equivalence.
+ *
+ * config_wire_equal() is generated from the SAME CONFIG_WIRE_FIELDS table as
+ * the serializer, so it can never miss a serialized field: adding a table
+ * entry automatically extends this comparison.  Each KIND maps to a comparison
+ * macro; STR_OPT/STR_KEEP normalize the NULL-vs-"" canonicalization the
+ * receiver performs, RAW_MAXALLOC models the server-side clamp, and
+ * DERIVED_DELTA compares the effective (whole_file-suppressed) bit.
+ * ------------------------------------------------------------------------- */
+static void golden_config_populate(Config* c);
+
+static bool str_opt_equal(const char* a, const char* b) {
+  if (a == NULL || a[0] == '\0')
+    return b == NULL || b[0] == '\0';
+  return b != NULL && strcmp(a, b) == 0;
+}
+
+static bool idmap_equal(const IdentityMap* a, int ac, const IdentityMap* b, int bc) {
+  if (ac != bc)
+    return false;
+  for (int i = 0; i < ac; i++) {
+    if (a[i].from != b[i].from || a[i].to != b[i].to)
+      return false;
+  }
+  return true;
+}
+
+static bool skip_suffixes_equal(const Config* a, const Config* b) {
+  if (a->skip_compress_count != b->skip_compress_count)
+    return false;
+  for (int i = 0; i < a->skip_compress_count; i++) {
+    if (!str_opt_equal(a->skip_compress_suffixes[i], b->skip_compress_suffixes[i]))
+      return false;
+  }
+  return true;
+}
+
+static bool basis_equal(const Config* a, const Config* b) {
+  if (a->basis_count != b->basis_count)
+    return false;
+  for (int i = 0; i < a->basis_count; i++) {
+    if (a->basis_dirs[i].type != b->basis_dirs[i].type ||
+        !str_opt_equal(a->basis_dirs[i].path, b->basis_dirs[i].path))
+      return false;
+  }
+  return true;
+}
+
+#define CONFIG_CMP_BOOL(a, b, name) ((a)->name == (b)->name)
+#define CONFIG_CMP_INT(a, b, name) ((a)->name == (b)->name)
+#define CONFIG_CMP_RAW(a, b, name) ((a)->name == (b)->name)
+#define CONFIG_CMP_BOOL_8BIT(a, b, name) ((a)->name == (b)->name)
+#define CONFIG_CMP_RAW_MAXALLOC(a, b, name)                                                        \
+  ((b)->name == ((a)->name > MAX_SERVER_ALLOC ? MAX_SERVER_ALLOC : (a)->name))
+#define CONFIG_CMP_DERIVED_DELTA(a, b, name) ((b)->name == ((a)->name && !(a)->whole_file))
+#define CONFIG_CMP_STR(a, b, name)                                                                 \
+  ((a)->name != NULL && (b)->name != NULL && strcmp((a)->name, (b)->name) == 0)
+#define CONFIG_CMP_STR_OPT(a, b, name) str_opt_equal((a)->name, (b)->name)
+#define CONFIG_CMP_STR_KEEP(a, b, name) str_opt_equal((a)->name, (b)->name)
+#define CONFIG_CMP_STR_MODULE(a, b, name) str_opt_equal((a)->name, (b)->name)
+#define CONFIG_CMP_STR_REDACTED_AUTH(a, b, name) str_opt_equal((a)->name, (b)->name)
+#define CONFIG_CMP_INT_CHECKSUM_ALGO(a, b, name) ((a)->name == (b)->name)
+#define CONFIG_CMP_SUPERMODE(a, b, name) ((a)->name == (b)->name)
+#define CONFIG_CMP_INT_IDENTITY(a, b, name) ((a)->name == (b)->name)
+#define CONFIG_CMP_INT_SKIPCOUNT(a, b, name) ((a)->name == (b)->name)
+#define CONFIG_CMP_INT_BASISCOUNT(a, b, name) ((a)->name == (b)->name)
+#define CONFIG_CMP_INT_IDMAPCOUNT(a, b, name) ((a)->name == (b)->name)
+#define CONFIG_CMP_BOOL_XATTR_DERIVE(a, b, name) ((a)->name == (b)->name)
+#define CONFIG_CMP_COPY_AS_PRESENCE(a, b, name) ((a)->name == (b)->name)
+#define CONFIG_CMP_COPY_AS_ID(a, b, name) (!(a)->copy_as_set || (a)->name == (b)->name)
+#define CONFIG_CMP_BLOCK_SKIP_SUFFIXES(a, b, name) skip_suffixes_equal((a), (b))
+#define CONFIG_CMP_BLOCK_BASIS(a, b, name) basis_equal((a), (b))
+#define CONFIG_CMP_BLOCK_IDMAP(a, b, name)                                                         \
+  idmap_equal((a)->name, (a)->name##_count, (b)->name, (b)->name##_count)
+
+#define WIRE_CMP(name, ctype, def, kind)                                                           \
+  &&(CONFIG_CMP_##kind(a, b, name)                                                                 \
+         ? true                                                                                    \
+         : (fprintf(stderr, "    mismatched field: %s\n", #name), false))
+
+static bool config_wire_equal(const Config* a, const Config* b) {
+  return true CONFIG_WIRE_FIELDS(WIRE_CMP);
+}
+
+static bool roundtrip_and_compare(const Config* send_cfg) {
+  int p[2];
+  if (socketpair(AF_UNIX, SOCK_STREAM, 0, p) != 0)
+    return false;
+  pid_t pid = fork();
+  if (pid == 0) {
+    close(p[1]);
+    io_set_fds(p[0], p[0]);
+    io_set_bwlimit(0);
+    Config* recv = config_receive(p[0]);
+    bool equal = recv != NULL && config_wire_equal(send_cfg, recv);
+    config_delete(recv);
+    close(p[0]);
+    _exit(equal ? 0 : 1);
+  }
+  close(p[0]);
+  io_set_fds(p[1], p[1]);
+  io_set_bwlimit(0);
+  bool sent = config_send(p[1], send_cfg);
+  int status;
+  waitpid(pid, &status, 0);
+  close(p[1]);
+  return sent && WIFEXITED(status) && WEXITSTATUS(status) == 0;
+}
+
+/* Every serialized field must survive a frame round-trip, for a defaults config
+ * and for a fully-populated config. */
+static void test_config_wire_roundtrip_all_fields() {
+  if (is_running_under_valgrind())
+    return;
+
+  Config* defaults = config_create();
+  EXPECT_NOT_NULL(defaults);
+  defaults->send_directory = str_dup("/src");
+  defaults->receive_root_directory = str_dup("/dst");
+  EXPECT_TRUE(roundtrip_and_compare(defaults));
+  config_delete(defaults);
+
+  Config* populated = config_create();
+  EXPECT_NOT_NULL(populated);
+  /* The golden fixture is already receiver-valid, so the same fully-populated
+   * config that backs the byte-exact golden also round-trips unchanged. */
+  golden_config_populate(populated);
+  EXPECT_TRUE(roundtrip_and_compare(populated));
+  config_delete(populated);
+}
+
+/* Populate every serialized field with a non-default value so the wire frame
+ * exercises each table entry.  Boolean runs deliberately alternate true/false:
+ * a run of identical booleans would make an adjacent swap (same KIND) produce
+ * the same byte stream, hiding a table reorder from the golden hash.  The whole
+ * frame stays receiver-valid so the receive-side golden can feed it straight
+ * through config_receive() (hence the valid chmod grammar and delta bound). */
+static void golden_config_populate(Config* c) {
+  c->eight_bit_output = true;
+  c->max_alloc = 123456789ULL;
+  c->send_directory = str_dup("/golden/src");
+  c->receive_root_directory = str_dup("/golden/dst");
+  c->save_to_disk = true;
+  c->use_multithreading = false;
+  c->use_chunk_serialization = false;
+  c->use_compression = true;
+  c->use_metadata = true;
+  c->use_executability = false;
+  c->compression_level = 7;
+  c->chunk_size = 65536;
+  c->use_sendfile = false;
+  c->use_delete = true;
+  c->use_incremental = true;
+  c->size_only = false;
+  c->ignore_times = true;
+  c->use_delta = true;
+  c->whole_file = false;
+  c->delta_block_size = 4096;
+  c->delta_max_file_size = 200000000ULL;
+  c->backup = true;
+  c->backup_dir = str_dup("/golden/backup");
+  c->remove_source_files = false;
+  c->follow_symlinks = true;
+  c->copy_links = false;
+  c->safe_links = true;
+  c->copy_unsafe_links = false;
+  c->preserve_hard_links = true;
+  c->preserve_acls = false;
+  c->preserve_xattrs = true;
+  c->preserve_devices = false;
+  c->preserve_sparse = true;
+  c->preserve_specials = false;
+  c->copy_devices = true;
+  c->write_devices = false;
+  c->ignore_existing = true;
+  c->existing = false;
+  c->update = true;
+  c->inplace = false;
+  c->delay_updates = true;
+  c->append = false;
+  c->use_fsync = true;
+  c->append_verify = false;
+  c->delete_excluded = true;
+  c->force_delete = false;
+  c->delete_missing_args = true;
+  c->delete_after = false;
+  c->preallocate = true;
+  c->max_delete = 42;
+  c->relative = false;
+  c->prune_empty_dirs = true;
+  c->mkpath = false;
+  c->delete_during = true;
+  c->delete_delay = false;
+  c->temp_dir = str_dup("/golden/tmp");
+  c->partial = true;
+  c->partial_dir = str_dup("/golden/partial");
+  c->suffix = str_dup(".golden");
+  c->delete_before = false;
+  c->checksum = true;
+  c->modify_window = 3;
+  c->compress_choice = str_dup("zstd");
+  /* "u=rwx,go=rx" is the same 11 bytes as the original "u=rwX,go=rX" (so the
+   * frame stays 633 bytes) but X is not in FastSync's chmod grammar, and the
+   * receive-side golden validates the frame. */
+  c->chmod_spec = str_dup("u=rwx,go=rx");
+  c->skip_compress_set = true;
+  c->skip_compress_count = 2;
+  c->skip_compress_suffixes = calloc(2, sizeof(char*));
+  c->skip_compress_suffixes[0] = str_dup(".gz");
+  c->skip_compress_suffixes[1] = str_dup(".xz");
+  EXPECT_EQ_INT(config_basis_append(c, BASIS_DEST_COMPARE, "compare"), 0);
+  EXPECT_EQ_INT(config_basis_append(c, BASIS_DEST_LINK, "link"), 0);
+  c->fuzzy = true;
+  c->checksum_algo = CHECKSUM_ALGO_MD5;
+  c->checksum_seed = 0x1122334455667788ULL;
+  c->numeric_ids = true;
+  c->chown_uid_set = false;
+  c->chown_uid = 1234;
+  c->chown_gid_set = true;
+  c->chown_gid = 5678;
+  c->usermap_count = 2;
+  c->usermap = calloc(2, sizeof(IdentityMap));
+  c->usermap[0].from = IDENTITY_MATCH_ANY;
+  c->usermap[0].to = 1000;
+  c->usermap[1].from = 5;
+  c->usermap[1].to = 6;
+  c->groupmap_count = 1;
+  c->groupmap = calloc(1, sizeof(IdentityMap));
+  c->groupmap[0].from = 7;
+  c->groupmap[0].to = 8;
+  c->preserve_atimes = true;
+  c->preserve_crtimes = false;
+  c->omit_dir_times = true;
+  c->omit_link_times = false;
+  c->munge_links = true;
+  c->keep_dirlinks = false;
+  c->fake_super = true;
+  c->module = str_dup("goldenmod");
+  c->auth_user = str_dup("goldenuser");
+  c->auth_password = str_dup("golden-pw");
+  c->iconv_spec = str_dup("UTF-8,UTF-8");
+  c->super_mode = SUPER_MODE_ON;
+  c->copy_as_set = true;
+  c->copy_as_uid = 111;
+  c->copy_as_gid = 222;
+}
+
+/* The pinned golden frame (protocol 2.20.0).  The values below are the only
+ * thing that ties the generated table to the historical wire format; update
+ * them ONLY with a PROTOCOL_VERSION bump and a documented reason. */
+#define GOLDEN_WIRE_LEN 633
+#define GOLDEN_WIRE_HASH 9160991280011164139ULL
+
+static unsigned long long fnv1a_64(const unsigned char* buf, size_t len) {
+  unsigned long long h = 1469598103934665603ULL;
+  for (size_t i = 0; i < len; i++) {
+    h ^= (unsigned long long)buf[i];
+    h *= 1099511628211ULL;
+  }
+  return h;
+}
+
+/* Capture the exact config-frame body emitted by config_send_wire_block() into
+ * a heap buffer.  Returns NULL on any failure. */
+static unsigned char* capture_wire_bytes(const Config* cfg, size_t* out_len) {
+  int p[2];
+  if (socketpair(AF_UNIX, SOCK_STREAM, 0, p) != 0)
+    return NULL;
+  pid_t pid = fork();
+  if (pid == 0) {
+    close(p[1]);
+    io_set_fds(p[0], p[0]);
+    io_set_bwlimit(0);
+    bool ok = config_send_wire_block(p[0], cfg);
+    close(p[0]);
+    _exit(ok ? 0 : 1);
+  }
+  close(p[0]);
+  size_t capacity = 1024;
+  size_t total = 0;
+  unsigned char* bytes = malloc(capacity);
+  if (!bytes) {
+    close(p[1]);
+    waitpid(pid, NULL, 0);
+    return NULL;
+  }
+  for (;;) {
+    if (total == capacity) {
+      size_t grown_capacity = capacity * 2;
+      unsigned char* grown = realloc(bytes, grown_capacity);
+      if (!grown) {
+        free(bytes);
+        close(p[1]);
+        waitpid(pid, NULL, 0);
+        return NULL;
+      }
+      bytes = grown;
+      capacity = grown_capacity;
+    }
+    ssize_t n = read(p[1], bytes + total, capacity - total);
+    if (n < 0) {
+      free(bytes);
+      close(p[1]);
+      waitpid(pid, NULL, 0);
+      return NULL;
+    }
+    if (n == 0)
+      break;
+    total += (size_t)n;
+  }
+  close(p[1]);
+  int status = 0;
+  waitpid(pid, &status, 0);
+  if (!WIFEXITED(status) || WEXITSTATUS(status) != 0) {
+    free(bytes);
+    return NULL;
+  }
+  *out_len = total;
+  return bytes;
+}
+
+/* FNV-1a 64 over the exact config-frame bytes emitted by
+ * config_send_wire_block().  This pins field order and width: any reorder or
+ * resize changes the hash. */
+static unsigned long long capture_wire_hash(const Config* cfg, size_t* out_len) {
+  unsigned char* bytes = capture_wire_bytes(cfg, out_len);
+  if (!bytes)
+    return 0;
+  unsigned long long h = fnv1a_64(bytes, *out_len);
+  free(bytes);
+  return h;
+}
+
+/* Byte-for-byte wire compatibility guard (protocol 2.20.0).  The expected hash
+ * pins the pre-X-macro byte stream; the refactor MUST NOT change it. */
+static void test_config_wire_golden() {
+  if (is_running_under_valgrind())
+    return;
+  Config* c = config_create();
+  EXPECT_NOT_NULL(c);
+  golden_config_populate(c);
+  size_t len = 0;
+  unsigned long long h = capture_wire_hash(c, &len);
+  printf("    wire golden: len=%zu hash=%llu\n", len, h);
+  EXPECT_TRUE(len == GOLDEN_WIRE_LEN);
+  EXPECT_TRUE(h == GOLDEN_WIRE_HASH);
+  config_delete(c);
+}
+
+/* Receive-side oracle.  Hashing the sender alone cannot catch a RECV KIND that
+ * reads a different width/order yet still round-trips symmetrically, so feed
+ * the SAME hash-pinned golden bytes through config_receive() and assert both
+ * the decoded struct fields and the derived bits.  Because the bytes are
+ * anchored to the send golden, a divergence on either side fails here. */
+static void test_config_wire_golden_receive() {
+  if (is_running_under_valgrind())
+    return;
+  Config* c = config_create();
+  EXPECT_NOT_NULL(c);
+  golden_config_populate(c);
+
+  size_t len = 0;
+  unsigned char* bytes = capture_wire_bytes(c, &len);
+  EXPECT_NOT_NULL(bytes);
+  EXPECT_TRUE(len == GOLDEN_WIRE_LEN);
+  EXPECT_TRUE(fnv1a_64(bytes, len) == GOLDEN_WIRE_HASH);
+
+  int p[2];
+  EXPECT_EQ_INT(socketpair(AF_UNIX, SOCK_STREAM, 0, p), 0);
+  io_set_fds(p[0], p[1]);
+  io_set_bwlimit(0);
+  pid_t pid = fork();
+  if (pid == 0) {
+    close(p[1]);
+    io_set_fds(p[0], p[0]);
+    io_set_bwlimit(0);
+    Config* recv = config_receive(p[0]);
+    bool ok = recv != NULL;
+    if (ok) {
+      /* Full field-by-field comparison (generated from CONFIG_WIRE_FIELDS). */
+      ok = config_wire_equal(c, recv);
+      /* Explicit spot checks of the decoded struct, including derived bits. */
+      ok = ok && recv->eight_bit_output && recv->use_compression && recv->use_metadata &&
+           !recv->use_multithreading;
+      ok = ok && recv->compression_level == 7 && recv->chunk_size == 65536;
+      ok = ok && recv->use_delta && !recv->whole_file && recv->use_xattrs;
+      /* Bounded/validated KINDs decoded from the pinned bytes. */
+      ok = ok && recv->checksum_algo == CHECKSUM_ALGO_MD5;
+      ok = ok && recv->super_mode == SUPER_MODE_ON;
+      ok = ok && recv->chown_uid == 1234 && recv->chown_gid == 5678;
+      ok = ok && recv->usermap_count == 2 && recv->usermap[0].from == IDENTITY_MATCH_ANY &&
+           recv->usermap[0].to == 1000 && recv->usermap[1].from == 5 && recv->usermap[1].to == 6;
+      ok = ok && recv->basis_count == 2 && recv->basis_dirs[0].type == BASIS_DEST_COMPARE &&
+           recv->basis_dirs[1].type == BASIS_DEST_LINK;
+      ok = ok && recv->module != NULL && strcmp(recv->module, "goldenmod") == 0;
+      ok = ok && recv->copy_as_set && recv->copy_as_uid == 111 && recv->copy_as_gid == 222;
+    }
+    config_delete(recv);
+    close(p[0]);
+    _exit(ok ? 0 : 1);
+  }
+  close(p[0]);
+  io_set_fds(p[1], p[1]);
+  io_set_bwlimit(0);
+  size_t written = 0;
+  bool wrote = true;
+  while (written < len) {
+    ssize_t n = write(p[1], bytes + written, len - written);
+    if (n <= 0) {
+      wrote = false;
+      break;
+    }
+    written += (size_t)n;
+  }
+  Status status = STATUS_ERROR;
+  bool got_status = wrote && receive_status(p[1], &status);
+  close(p[1]);
+  free(bytes);
+  int child_status = 0;
+  waitpid(pid, &child_status, 0);
+  EXPECT_TRUE(got_status && status == STATUS_OK);
+  EXPECT_TRUE(WIFEXITED(child_status) && WEXITSTATUS(child_status) == 0);
+  config_delete(c);
+}
+
+/* Hand-build a frame that is valid up to the first core BOOL, then write an
+ * out-of-range boolean (2): a BOOL receiver must reject anything but 0/1. */
+static void write_frame_with_invalid_bool(int fd) {
+  send_str(fd, PROTOCOL_VERSION);
+  send_int(fd, 1); /* eight_bit_output */
+  unsigned long long max_alloc = DEFAULT_MAX_ALLOC;
+  send_n_data(fd, &max_alloc, sizeof(max_alloc));
+  send_str(fd, "/src");
+  send_str(fd, "/dst");
+  send_int(fd, 2); /* save_to_disk: not 0/1 */
+}
+
+/* Feed a caller-built frame into config_receive() and report whether the
+ * receiver rejected it.  The writer runs in a child (SIGPIPE ignored) so a
+ * mid-frame rejection cannot kill the test process. */
+static bool receive_hand_built_frame_rejected(void (*write_frame)(int fd)) {
+  int p[2];
+  if (socketpair(AF_UNIX, SOCK_STREAM, 0, p) != 0)
+    return false;
+  pid_t pid = fork();
+  if (pid == 0) {
+    (void)signal(SIGPIPE, SIG_IGN);
+    close(p[0]);
+    io_set_fds(p[1], p[1]);
+    io_set_bwlimit(0);
+    write_frame(p[1]);
+    close(p[1]);
+    _exit(0);
+  }
+  close(p[1]);
+  io_set_fds(p[0], p[0]);
+  io_set_bwlimit(0);
+  Config* recv = config_receive(p[0]);
+  bool rejected = recv == NULL;
+  config_delete(recv);
+  close(p[0]);
+  int status = 0;
+  waitpid(pid, &status, 0);
+  return rejected;
+}
+
+/* Receive-side bounds for the bounded/validated KINDs that the round-trip
+ * helper cannot exercise (an illegal value has no symmetric sender). */
+static void test_config_wire_receive_bounds() {
+  if (is_running_under_valgrind())
+    return;
+
+  /* BOOL: only 0/1 is a legal wire value. */
+  EXPECT_TRUE(receive_hand_built_frame_rejected(write_frame_with_invalid_bool));
+
+  /* RAW_MAXALLOC: zero is rejected before it can become the session ceiling. */
+  Config* c = config_create();
+  EXPECT_NOT_NULL(c);
+  c->send_directory = str_dup("/src");
+  c->receive_root_directory = str_dup("/dst");
+  c->max_alloc = 0;
+  EXPECT_TRUE(roundtrip_config_rejected(c));
+  config_delete(c);
+
+  /* STR_MODULE: a name outside [A-Za-z0-9._-] is refused. */
+  c = config_create();
+  EXPECT_NOT_NULL(c);
+  c->send_directory = str_dup("/src");
+  c->receive_root_directory = str_dup("/dst");
+  c->module = str_dup("bad module");
+  EXPECT_TRUE(roundtrip_config_rejected(c));
+  config_delete(c);
+
+  /* INT_IDMAPCOUNT: one past the identity-map cap is refused at the count. */
+  c = config_create();
+  EXPECT_NOT_NULL(c);
+  c->send_directory = str_dup("/src");
+  c->receive_root_directory = str_dup("/dst");
+  c->usermap_count = MAX_IDENTITY_MAP + 1;
+  c->usermap = calloc((size_t)c->usermap_count, sizeof(IdentityMap));
+  if (c->usermap) {
+    for (int i = 0; i < c->usermap_count; i++) {
+      c->usermap[i].from = 0;
+      c->usermap[i].to = 0;
+    }
+  }
+  EXPECT_TRUE(roundtrip_config_rejected(c));
+  config_delete(c);
+
+  /* INT_IDENTITY: an out-of-range chown_uid (below IDENTITY_MATCH_ANY) is
+   * refused by the identity validator. */
+  c = config_create();
+  EXPECT_NOT_NULL(c);
+  c->send_directory = str_dup("/src");
+  c->receive_root_directory = str_dup("/dst");
+  c->chown_uid_set = true;
+  c->chown_uid = IDENTITY_MATCH_ANY - 1;
+  EXPECT_TRUE(roundtrip_config_rejected(c));
+  config_delete(c);
+}
+
+/* Regression (pre-auth NULL-deref): the *_count receive helpers used to write
+ * the peer-controlled int through the Config member BEFORE validating it.  An
+ * over-cap basis_count therefore left config->basis_count huge while
+ * config->basis_dirs stayed NULL; the config_receive() error path then called
+ * config_delete(), whose `for (i < basis_count) free(basis_dirs[i].path)` loop
+ * dereferenced NULL.  A malicious client could crash the daemon before auth.
+ *
+ * The helpers now validate a LOCAL and publish only on success, so a rejected
+ * count leaves the member at its safe default (0).  The idmap/skip helpers have
+ * the same "write then validate" shape and are covered here too, as is the
+ * config_delete() NULL-array guard that backstops the whole class. */
+static void test_config_receive_rejects_overcap_counts() {
+  if (is_running_under_valgrind())
+    return;
+
+  /* Over-cap basis count.  The values are injected directly (config_basis_append
+   * enforces the cap) with a matching array so the sender can emit the block;
+   * the receiver must reject at the count and remain crash-free while deleting
+   * the partially populated Config. */
+  Config* c = config_create();
+  EXPECT_NOT_NULL(c);
+  c->send_directory = str_dup("/src");
+  c->receive_root_directory = str_dup("/dst");
+  c->basis_count = MAX_BASIS_DIRS + 1;
+  c->basis_dirs = calloc((size_t)c->basis_count, sizeof(BasisDest));
+  EXPECT_NOT_NULL(c->basis_dirs);
+  for (int i = 0; i < c->basis_count; i++) {
+    c->basis_dirs[i].type = BASIS_DEST_LINK;
+    c->basis_dirs[i].path = str_dup("basis");
+  }
+  EXPECT_TRUE(roundtrip_config_rejected(c));
+  config_delete(c);
+
+  /* Over-cap identity-map count (usermap and groupmap share the helper). */
+  c = config_create();
+  EXPECT_NOT_NULL(c);
+  c->send_directory = str_dup("/src");
+  c->receive_root_directory = str_dup("/dst");
+  c->usermap_count = MAX_IDENTITY_MAP + 1;
+  c->usermap = calloc((size_t)c->usermap_count, sizeof(IdentityMap));
+  EXPECT_NOT_NULL(c->usermap);
+  for (int i = 0; i < c->usermap_count; i++) {
+    c->usermap[i].from = 0;
+    c->usermap[i].to = 0;
+  }
+  EXPECT_TRUE(roundtrip_config_rejected(c));
+  config_delete(c);
+
+  /* Over-cap skip-compress count. */
+  Config* over_skip = make_skip_compress_config(MAX_SKIP_COMPRESS_SUFFIXES + 1, 1);
+  EXPECT_NOT_NULL(over_skip);
+  EXPECT_TRUE(roundtrip_config_rejected(over_skip));
+  config_delete(over_skip);
+
+  /* Defense-in-depth: config_delete() on a Config left with a non-zero count
+   * but a NULL array (the exact partial state an over-cap count used to leave
+   * behind) must be safe. */
+  c = config_create();
+  EXPECT_NOT_NULL(c);
+  c->basis_count = MAX_BASIS_DIRS + 1;
+  c->basis_dirs = NULL;
+  config_delete(c);
+}
+
 void test_config() {
   test_config_lifecycle();
   test_config_ssh_dest();
@@ -2249,6 +2836,11 @@ void test_config() {
     test_config_receive_with_validate_rejects();
     test_config_invariants_error_all_combinations();
     test_config_receive_rejects_unified_invariants();
+    test_config_wire_golden();
+    test_config_wire_golden_receive();
+    test_config_wire_receive_bounds();
+    test_config_receive_rejects_overcap_counts();
+    test_config_wire_roundtrip_all_fields();
   }
   test_identity_copy_as_refused();
   test_identity_ownership_requested();

tests/test_daemon_conf.c

@@ -33,6 +33,11 @@ static void test_daemon_conf_create_defaults() {
   EXPECT_NULL(conf->global.address);
   EXPECT_EQ_INT(conf->global.max_connections, DAEMON_CONF_DEFAULT_MAX_CONNECTIONS);
   EXPECT_EQ_INT(conf->global.auth_failure_delay_ms, DAEMON_CONF_DEFAULT_AUTH_FAILURE_DELAY_MS);
+  EXPECT_EQ_INT(conf->global.max_connections_per_host,
+                DAEMON_CONF_DEFAULT_MAX_CONNECTIONS_PER_HOST);
+  EXPECT_EQ_INT(conf->global.auth_lockout_threshold, DAEMON_CONF_DEFAULT_AUTH_LOCKOUT_THRESHOLD);
+  EXPECT_EQ_INT(conf->global.auth_lockout_duration_sec,
+                DAEMON_CONF_DEFAULT_AUTH_LOCKOUT_DURATION_SEC);
   EXPECT_EQ_INT(conf->global.hosts_allow_count, 0);
   EXPECT_EQ_INT(conf->global.hosts_deny_count, 0);
   EXPECT_EQ_INT(conf->module_count, 0);
@@ -316,6 +321,12 @@ static void test_daemon_conf_dparam_override() {
 
   EXPECT_EQ_INT(daemon_conf_apply_dparam(conf, "max connections=7", err, sizeof(err)), 0);
   EXPECT_EQ_INT(conf->global.max_connections, 7);
+  EXPECT_EQ_INT(daemon_conf_apply_dparam(conf, "max connections per host=3", err, sizeof(err)), 0);
+  EXPECT_EQ_INT(conf->global.max_connections_per_host, 3);
+  EXPECT_EQ_INT(daemon_conf_apply_dparam(conf, "auth lockout threshold=5", err, sizeof(err)), 0);
+  EXPECT_EQ_INT(conf->global.auth_lockout_threshold, 5);
+  EXPECT_EQ_INT(daemon_conf_apply_dparam(conf, "auth lockout duration=120", err, sizeof(err)), 0);
+  EXPECT_EQ_INT(conf->global.auth_lockout_duration_sec, 120);
   EXPECT_EQ_INT(daemon_conf_apply_dparam(conf, "AUTH FAILURE DELAY=1500", err, sizeof(err)), 0);
   EXPECT_EQ_INT(conf->global.auth_failure_delay_ms, 1500);
   EXPECT_EQ_INT(
@@ -390,6 +401,9 @@ static void test_daemon_conf_limits_and_hosts_parse() {
   char err[256];
   EXPECT_EQ_INT(write_conf("max connections = 25\n"
                            "auth failure delay = 0\n"
+                           "max connections per host = 4\n"
+                           "auth lockout threshold = 3\n"
+                           "auth lockout duration = 60\n"
                            "hosts allow = 10.0.0.0/8, 192.168.1.0/24\n"
                            "hosts deny = 192.168.0.1 2001:db8::/32\n"
                            "\n"
@@ -405,6 +419,9 @@ static void test_daemon_conf_limits_and_hosts_parse() {
   EXPECT_NOT_NULL(conf);
   EXPECT_EQ_INT(conf->global.max_connections, 25);
   EXPECT_EQ_INT(conf->global.auth_failure_delay_ms, 0);
+  EXPECT_EQ_INT(conf->global.max_connections_per_host, 4);
+  EXPECT_EQ_INT(conf->global.auth_lockout_threshold, 3);
+  EXPECT_EQ_INT(conf->global.auth_lockout_duration_sec, 60);
   EXPECT_EQ_INT(conf->global.hosts_allow_count, 2);
   EXPECT_EQ_STR(conf->global.hosts_allow[0], "10.0.0.0/8");
   EXPECT_EQ_STR(conf->global.hosts_allow[1], "192.168.1.0/24");
@@ -419,11 +436,14 @@ static void test_daemon_conf_limits_and_hosts_parse() {
   daemon_conf_free(conf);
 
   const char* bad_values[] = {
-      "max connections = 0\n",         "max connections = -1\n",
+      "max connections = 0\n",           "max connections = -1\n",
-      "max connections = abc\n",       "auth failure delay = -1\n",
+      "max connections = abc\n",         "auth failure delay = -1\n",
-      "auth failure delay = 70000\n",  "auth failure delay = soon\n",
+      "auth failure delay = 70000\n",    "auth failure delay = soon\n",
-      "hosts allow = 10.0.0.0/99\n",   "hosts deny = 2001:db8::/129\n",
+      "max connections per host = -1\n", "max connections per host = lots\n",
-      "hosts allow = *.example.com\n", "hosts deny = not-an-ip\n",
+      "auth lockout threshold = -2\n",   "auth lockout threshold = many\n",
+      "auth lockout duration = -1\n",    "auth lockout duration = forever\n",
+      "hosts allow = 10.0.0.0/99\n",     "hosts deny = 2001:db8::/129\n",
+      "hosts allow = *.example.com\n",   "hosts deny = not-an-ip\n",
   };
   for (size_t i = 0; i < sizeof(bad_values) / sizeof(bad_values[0]); i++) {
     EXPECT_EQ_INT(write_conf(bad_values[i], &path), 0);
@@ -434,7 +454,8 @@ static void test_daemon_conf_limits_and_hosts_parse() {
 
   /* The same strictness applies inside a module section. */
   const char* bad_module[] = {
-      "[m]\npath = /x\nmax connections = 0\n",
+      "[m]\npath = /x\nmax connections = -1\n",
+      "[m]\npath = /x\nmax connections = abc\n",
       "[m]\npath = /x\nhosts allow = 10.0.0.0/40\n",
       "[m]\npath = /x\nhosts deny = 999.1.1.1/8\n",
   };
@@ -446,6 +467,14 @@ static void test_daemon_conf_limits_and_hosts_parse() {
     EXPECT_TRUE(strstr(err, "invalid") != NULL);
   }
 
+  /* Module `max connections = 0` is now valid and means unlimited. */
+  EXPECT_EQ_INT(write_conf("[m]\npath = /x\nmax connections = 0\n", &path), 0);
+  conf = daemon_conf_load(path, err, sizeof(err));
+  free(path);
+  EXPECT_NOT_NULL(conf);
+  EXPECT_EQ_INT(conf->modules[0].max_connections, 0);
+  daemon_conf_free(conf);
+
   /* An empty hosts list is not an error (no patterns are added). */
   EXPECT_EQ_INT(write_conf("hosts allow = \n[m]\npath = /x\n", &path), 0);
   conf = daemon_conf_load(path, err, sizeof(err));
@@ -509,6 +538,35 @@ static void test_daemon_module_name_valid() {
   }
 }
 
+static void test_daemon_conf_module_count_capped() {
+  size_t cap = DAEMON_CONF_MAX_MODULES;
+  size_t len = (cap + 8) * 32;
+  char* body = malloc(len);
+  EXPECT_NOT_NULL(body);
+  size_t used = 0;
+  body[0] = '\0';
+  for (size_t i = 0; i < cap + 1; i++) {
+    char line[48];
+    int n = snprintf(line, sizeof(line), "[m%zu]\npath = /x\n", i);
+    if (n < 0 || (size_t)n >= sizeof(line) || used + (size_t)n >= len) {
+      free(body);
+      EXPECT_FAIL("module-count test buffer overflow");
+      return;
+    }
+    memcpy(body + used, line, (size_t)n);
+    used += (size_t)n;
+    body[used] = '\0';
+  }
+  char* path;
+  EXPECT_EQ_INT(write_conf(body, &path), 0);
+  free(body);
+  char err[256];
+  const DaemonConf* conf = daemon_conf_load(path, err, sizeof(err));
+  free(path);
+  EXPECT_NULL(conf);
+  EXPECT_TRUE(strstr(err, "too many modules") != NULL);
+}
+
 void test_daemon_conf() {
   test_daemon_conf_create_defaults();
   test_daemon_conf_full_parse();
@@ -525,6 +583,7 @@ void test_daemon_conf() {
   test_daemon_conf_dparam_override();
   test_daemon_conf_auth_users_validated();
   test_daemon_conf_limits_and_hosts_parse();
+  test_daemon_conf_module_count_capped();
   test_daemon_hosts_allowed();
   test_daemon_module_name_valid();
 }

tests/test_daemon_limits.c

@@ -0,0 +1,311 @@
+#include "test_daemon_limits.h"
+#include "daemon_limits.h"
+#include "test_utils.h"
+#include <stdint.h>
+#include <stdio.h>
+#include <sys/wait.h>
+#include <time.h>
+#include <unistd.h>
+
+/* The per-source hash is a pure helper: numeric addresses hash to a nonzero,
+ * stable value and unparseable input reports failure. */
+static void test_daemon_limits_host_hash() {
+  bool ok = false;
+  uint64_t v4 = daemon_limits_host_hash("127.0.0.1", &ok);
+  EXPECT_TRUE(ok);
+  EXPECT_TRUE(v4 != 0);
+  EXPECT_EQ_INT((int)(daemon_limits_host_hash("127.0.0.1", NULL) == v4), 1);
+
+  bool ok6 = false;
+  uint64_t v6 = daemon_limits_host_hash("2001:db8::1", &ok6);
+  EXPECT_TRUE(ok6);
+  EXPECT_TRUE(v6 != 0);
+  /* Distinct textual forms of different addresses must differ. */
+  EXPECT_TRUE(v4 != v6);
+
+  bool bad = true;
+  EXPECT_TRUE(daemon_limits_host_hash("not-an-ip", &bad) == 0);
+  EXPECT_FALSE(bad);
+  bad = true;
+  EXPECT_TRUE(daemon_limits_host_hash(NULL, &bad) == 0);
+  EXPECT_FALSE(bad);
+  bad = true;
+  EXPECT_TRUE(daemon_limits_host_hash("", &bad) == 0);
+  EXPECT_FALSE(bad);
+}
+
+/* Slot reservation is a plain parent-side resource: claim until exhausted,
+ * reclaim, then claim again. */
+static void test_daemon_limits_slots() {
+  DaemonLimitRegistry* registry = daemon_limits_create(DAEMON_LIMITS_MIN_SLOTS, 2, 0, 0, 0);
+  EXPECT_NOT_NULL(registry);
+  int slots[DAEMON_LIMITS_MIN_SLOTS];
+  for (int i = 0; i < DAEMON_LIMITS_MIN_SLOTS; i++) {
+    slots[i] = daemon_limits_claim_slot(registry);
+    EXPECT_EQ_INT(slots[i], i);
+  }
+  EXPECT_EQ_INT(daemon_limits_claim_slot(registry), DAEMON_LIMITS_NO_SLOT);
+  daemon_limits_reclaim_slot(registry, slots[3]);
+  int reclaimed = daemon_limits_claim_slot(registry);
+  EXPECT_EQ_INT(reclaimed, slots[3]);
+  daemon_limits_destroy(registry);
+}
+
+/* Per-module accounting: the cap is enforced across slots and a reclaimed slot
+ * frees a module count. */
+static void test_daemon_limits_module_cap() {
+  DaemonLimitRegistry* registry = daemon_limits_create(DAEMON_LIMITS_MIN_SLOTS, 2, 0, 0, 0);
+  EXPECT_NOT_NULL(registry);
+
+  int slot0 = daemon_limits_claim_slot(registry);
+  int slot1 = daemon_limits_claim_slot(registry);
+  int slot2 = daemon_limits_claim_slot(registry);
+  int slot3 = daemon_limits_claim_slot(registry);
+  EXPECT_TRUE(slot0 >= 0 && slot1 >= 0 && slot2 >= 0 && slot3 >= 0);
+
+  EXPECT_EQ_INT(daemon_limits_register(registry, slot0, 0, "10.0.0.1", 2), DAEMON_LIMIT_OK);
+  EXPECT_EQ_INT(daemon_limits_register(registry, slot1, 0, "10.0.0.2", 2), DAEMON_LIMIT_OK);
+  EXPECT_EQ_INT(daemon_limits_register(registry, slot2, 0, "10.0.0.3", 2),
+                DAEMON_LIMIT_MODULE_FULL);
+  /* A different module has its own counter. */
+  EXPECT_EQ_INT(daemon_limits_register(registry, slot2, 1, "10.0.0.3", 2), DAEMON_LIMIT_OK);
+  /* A module cap of 0 is unlimited. */
+  EXPECT_EQ_INT(daemon_limits_register(registry, slot3, 0, "10.0.0.3", 0), DAEMON_LIMIT_OK);
+
+  daemon_limits_reclaim_slot(registry, slot0);
+  daemon_limits_reclaim_slot(registry, slot1);
+  daemon_limits_recompute(registry);
+  int slot4 = daemon_limits_claim_slot(registry);
+  EXPECT_TRUE(slot4 >= 0);
+  EXPECT_EQ_INT(daemon_limits_register(registry, slot4, 0, "10.0.0.4", 2), DAEMON_LIMIT_OK);
+
+  daemon_limits_destroy(registry);
+}
+
+/* Per-source accounting: the same peer hits the cap, a different peer does not. */
+static void test_daemon_limits_host_cap() {
+  DaemonLimitRegistry* registry = daemon_limits_create(DAEMON_LIMITS_MIN_SLOTS, 1, 1, 0, 0);
+  EXPECT_NOT_NULL(registry);
+
+  int slot0 = daemon_limits_claim_slot(registry);
+  int slot1 = daemon_limits_claim_slot(registry);
+  int slot2 = daemon_limits_claim_slot(registry);
+  EXPECT_TRUE(slot0 >= 0 && slot1 >= 0 && slot2 >= 0);
+
+  EXPECT_EQ_INT(daemon_limits_register(registry, slot0, 0, "10.0.0.1", 0), DAEMON_LIMIT_OK);
+  EXPECT_EQ_INT(daemon_limits_register(registry, slot1, 0, "10.0.0.1", 0), DAEMON_LIMIT_HOST_FULL);
+  EXPECT_EQ_INT(daemon_limits_register(registry, slot2, 0, "10.0.0.2", 0), DAEMON_LIMIT_OK);
+  /* Reclaiming the first source frees its per-host allowance. */
+  daemon_limits_reclaim_slot(registry, slot0);
+  daemon_limits_recompute(registry);
+  EXPECT_EQ_INT(daemon_limits_register(registry, slot1, 0, "10.0.0.1", 0), DAEMON_LIMIT_OK);
+
+  daemon_limits_destroy(registry);
+}
+
+/* The pid-indexed reclaim is what the parent's SIGCHLD handler uses: a dead
+ * child's module/source counts must be released. */
+static void test_daemon_limits_reclaim_pid() {
+  DaemonLimitRegistry* registry = daemon_limits_create(DAEMON_LIMITS_MIN_SLOTS, 1, 1, 0, 0);
+  EXPECT_NOT_NULL(registry);
+
+  int slot0 = daemon_limits_claim_slot(registry);
+  int slot1 = daemon_limits_claim_slot(registry);
+  EXPECT_TRUE(slot0 >= 0 && slot1 >= 0);
+  daemon_limits_set_slot_pid(registry, slot0, 4242);
+  EXPECT_EQ_INT(daemon_limits_register(registry, slot0, 0, "10.0.0.1", 1), DAEMON_LIMIT_OK);
+  /* Cap (module 1) and per-host (1) are both saturated. */
+  EXPECT_EQ_INT(daemon_limits_register(registry, slot1, 0, "10.0.0.1", 1),
+                DAEMON_LIMIT_MODULE_FULL);
+
+  daemon_limits_reclaim_pid(registry, 4242);
+  daemon_limits_recompute(registry);
+  EXPECT_EQ_INT(daemon_limits_register(registry, slot1, 0, "10.0.0.1", 1), DAEMON_LIMIT_OK);
+  /* Reclaiming an unknown pid is a no-op. */
+  daemon_limits_reclaim_pid(registry, 999999);
+
+  daemon_limits_destroy(registry);
+}
+
+/* Cross-process lockout: failures counted in the shared mapping lock the source
+ * out after the threshold; a success clears it; threshold 0 disables it. */
+static void test_daemon_limits_auth_lockout() {
+  DaemonLimitRegistry* registry = daemon_limits_create(DAEMON_LIMITS_MIN_SLOTS, 1, 0, 2, 300);
+  EXPECT_NOT_NULL(registry);
+
+  int remaining = 0;
+  EXPECT_FALSE(daemon_limits_auth_locked(registry, "10.0.0.1", &remaining));
+  daemon_limits_auth_record_failure(registry, "10.0.0.1");
+  EXPECT_FALSE(daemon_limits_auth_locked(registry, "10.0.0.1", &remaining));
+  daemon_limits_auth_record_failure(registry, "10.0.0.1");
+  EXPECT_TRUE(daemon_limits_auth_locked(registry, "10.0.0.1", &remaining));
+  EXPECT_TRUE(remaining > 0 && remaining <= 300);
+  /* Another source is unaffected. */
+  EXPECT_FALSE(daemon_limits_auth_locked(registry, "10.0.0.2", &remaining));
+  /* A successful authentication clears the lockout. */
+  daemon_limits_auth_record_success(registry, "10.0.0.1");
+  EXPECT_FALSE(daemon_limits_auth_locked(registry, "10.0.0.1", &remaining));
+  daemon_limits_destroy(registry);
+
+  /* threshold 0 disables the lockout entirely. */
+  registry = daemon_limits_create(DAEMON_LIMITS_MIN_SLOTS, 1, 0, 0, 300);
+  EXPECT_NOT_NULL(registry);
+  for (int i = 0; i < 50; i++)
+    daemon_limits_auth_record_failure(registry, "10.0.0.1");
+  EXPECT_FALSE(daemon_limits_auth_locked(registry, "10.0.0.1", &remaining));
+  daemon_limits_destroy(registry);
+}
+
+/* The registry must be visible across fork(): a child's registration is seen by
+ * the parent, and the parent's pid reclaim releases it. */
+static void test_daemon_limits_fork_shared() {
+  if (is_running_under_valgrind())
+    return; /* fork + shared mapping is slow/noisy under valgrind */
+  DaemonLimitRegistry* registry = daemon_limits_create(DAEMON_LIMITS_MIN_SLOTS, 1, 0, 0, 0);
+  EXPECT_NOT_NULL(registry);
+
+  int slot0 = daemon_limits_claim_slot(registry);
+  EXPECT_TRUE(slot0 >= 0);
+  pid_t pid = fork();
+  if (pid == 0) {
+    if (daemon_limits_register(registry, slot0, 0, "10.0.0.1", 1) != DAEMON_LIMIT_OK)
+      _exit(1);
+    _exit(0);
+  }
+  EXPECT_TRUE(pid > 0);
+  daemon_limits_set_slot_pid(registry, slot0, (long)pid);
+  int status = 0;
+  EXPECT_TRUE(waitpid(pid, &status, 0) == pid);
+  EXPECT_TRUE(WIFEXITED(status) && WEXITSTATUS(status) == 0);
+  /* The child's module count is still held in the shared mapping. */
+  int slot1 = daemon_limits_claim_slot(registry);
+  EXPECT_TRUE(slot1 >= 0);
+  EXPECT_EQ_INT(daemon_limits_register(registry, slot1, 0, "10.0.0.2", 1),
+                DAEMON_LIMIT_MODULE_FULL);
+  /* The parent reclaims the dead child's slot by pid. */
+  daemon_limits_reclaim_pid(registry, (long)pid);
+  daemon_limits_recompute(registry);
+  EXPECT_EQ_INT(daemon_limits_register(registry, slot1, 0, "10.0.0.2", 1), DAEMON_LIMIT_OK);
+  daemon_limits_destroy(registry);
+}
+
+/* Cross-process auth lockout: failures recorded by forked children against the
+ * shared mmap must lock the source out for the parent.  This is the
+ * cross-process path the integration test can no longer cover because trusted
+ * loopback peers are exempt from the per-host limits. */
+static void test_daemon_limits_fork_auth_lockout() {
+  if (is_running_under_valgrind())
+    return; /* fork + shared mapping is slow/noisy under valgrind */
+  DaemonLimitRegistry* registry = daemon_limits_create(DAEMON_LIMITS_MIN_SLOTS, 1, 0, 2, 300);
+  EXPECT_NOT_NULL(registry);
+
+  int remaining = 0;
+  EXPECT_FALSE(daemon_limits_auth_locked(registry, "10.0.0.1", &remaining));
+
+  /* One failure from each of two children reaches the threshold of 2 in the
+   * shared mapping; atomics only, no mtx/malloc, so fork-safe. */
+  for (int i = 0; i < 2; i++) {
+    pid_t pid = fork();
+    if (pid == 0) {
+      daemon_limits_auth_record_failure(registry, "10.0.0.1");
+      _exit(0);
+    }
+    EXPECT_TRUE(pid > 0);
+    int status = 0;
+    EXPECT_TRUE(waitpid(pid, &status, 0) == pid);
+    EXPECT_TRUE(WIFEXITED(status) && WEXITSTATUS(status) == 0);
+  }
+
+  /* The parent observes the lockout the children established. */
+  EXPECT_TRUE(daemon_limits_auth_locked(registry, "10.0.0.1", &remaining));
+  EXPECT_TRUE(remaining > 0 && remaining <= 300);
+  /* A different source is unaffected across processes. */
+  EXPECT_FALSE(daemon_limits_auth_locked(registry, "10.0.0.2", &remaining));
+  /* The parent clears the shared lockout on a successful authentication. */
+  daemon_limits_auth_record_success(registry, "10.0.0.1");
+  EXPECT_FALSE(daemon_limits_auth_locked(registry, "10.0.0.1", &remaining));
+  daemon_limits_destroy(registry);
+}
+
+/* The occupancy arrays are derived from the slot table: recompute rebuilds them
+ * and is the self-heal path the SIGCHLD handler uses after a child dies. */
+static void test_daemon_limits_recompute() {
+  DaemonLimitRegistry* registry = daemon_limits_create(DAEMON_LIMITS_MIN_SLOTS, 2, 1, 0, 0);
+  EXPECT_NOT_NULL(registry);
+  int slot0 = daemon_limits_claim_slot(registry);
+  int slot1 = daemon_limits_claim_slot(registry);
+  int slot2 = daemon_limits_claim_slot(registry);
+  EXPECT_TRUE(slot0 >= 0 && slot1 >= 0 && slot2 >= 0);
+  EXPECT_EQ_INT(daemon_limits_register(registry, slot0, 0, "10.0.0.1", 0), DAEMON_LIMIT_OK);
+  EXPECT_EQ_INT(daemon_limits_register(registry, slot1, 0, "10.0.0.2", 0), DAEMON_LIMIT_OK);
+
+  /* Recompute is idempotent and re-derives the same counts from REGISTERED
+   * slots (a CLAIMED slot is never counted). */
+  daemon_limits_recompute(registry);
+  daemon_limits_recompute(registry);
+  EXPECT_EQ_INT(daemon_limits_register(registry, slot2, 0, "10.0.0.3", 2),
+                DAEMON_LIMIT_MODULE_FULL);
+
+  /* Freeing a slot and recomputing releases its module/per-source count. */
+  daemon_limits_reclaim_slot(registry, slot0);
+  daemon_limits_recompute(registry);
+  EXPECT_EQ_INT(daemon_limits_register(registry, slot2, 0, "10.0.0.3", 2), DAEMON_LIMIT_OK);
+  daemon_limits_destroy(registry);
+}
+
+/* The per-source table has a bounded lifetime.  When every bucket is occupied
+ * but not yet reclaimable, a new source is fail-open: the per-host cap is not
+ * enforced and the probe must terminate.  Once the occupied buckets' lockouts
+ * expire (or they go idle), a new source reclaims a bucket and enforcement comes
+ * back.  This covers the "table never evicts -> cap silently fails open forever"
+ * review finding. */
+static void test_daemon_limits_host_table_eviction() {
+  char ip[32];
+
+  /* Part A: all buckets locked out with a long deadline and no active
+   * connection are not reclaimable yet.  A new source cannot be interned, so the
+   * per-host cap is documented fail-open (both connections admitted) -- and the
+   * bounded probe returns instead of looping forever. */
+  DaemonLimitRegistry* registry = daemon_limits_create(DAEMON_LIMITS_MIN_SLOTS, 1, 1, 1, 300);
+  EXPECT_NOT_NULL(registry);
+  for (int i = 0; i < 64; i++) {
+    snprintf(ip, sizeof(ip), "10.0.0.%d", i + 1);
+    daemon_limits_auth_record_failure(registry, ip);
+  }
+  int a = daemon_limits_claim_slot(registry);
+  int b = daemon_limits_claim_slot(registry);
+  EXPECT_TRUE(a >= 0 && b >= 0);
+  EXPECT_EQ_INT(daemon_limits_register(registry, a, 0, "10.9.9.9", 0), DAEMON_LIMIT_OK);
+  EXPECT_EQ_INT(daemon_limits_register(registry, b, 0, "10.9.9.9", 0), DAEMON_LIMIT_OK);
+  daemon_limits_destroy(registry);
+
+  /* Part B: with an already-expired lockout every bucket is reclaimable, so a
+   * new source reclaims one and the per-host cap is enforced again. */
+  registry = daemon_limits_create(DAEMON_LIMITS_MIN_SLOTS, 1, 1, 1, 1);
+  EXPECT_NOT_NULL(registry);
+  for (int i = 0; i < 64; i++) {
+    snprintf(ip, sizeof(ip), "10.0.0.%d", i + 1);
+    daemon_limits_auth_record_failure(registry, ip);
+  }
+  struct timespec pause = {2, 0};
+  nanosleep(&pause, NULL);
+  int c = daemon_limits_claim_slot(registry);
+  int d = daemon_limits_claim_slot(registry);
+  EXPECT_TRUE(c >= 0 && d >= 0);
+  EXPECT_EQ_INT(daemon_limits_register(registry, c, 0, "10.9.9.9", 0), DAEMON_LIMIT_OK);
+  EXPECT_EQ_INT(daemon_limits_register(registry, d, 0, "10.9.9.9", 0), DAEMON_LIMIT_HOST_FULL);
+  daemon_limits_destroy(registry);
+}
+
+void test_daemon_limits() {
+  test_daemon_limits_host_hash();
+  test_daemon_limits_slots();
+  test_daemon_limits_module_cap();
+  test_daemon_limits_host_cap();
+  test_daemon_limits_reclaim_pid();
+  test_daemon_limits_recompute();
+  test_daemon_limits_auth_lockout();
+  test_daemon_limits_host_table_eviction();
+  test_daemon_limits_fork_shared();
+  test_daemon_limits_fork_auth_lockout();
+}

tests/test_daemon_limits.h

@@ -0,0 +1,6 @@
+#ifndef TEST_DAEMON_LIMITS_H
+#define TEST_DAEMON_LIMITS_H
+
+void test_daemon_limits();
+
+#endif

tests/test_file.c

@@ -1180,7 +1180,7 @@ static void test_trust_sender_authorized_root_confinement() {
     rmdir(sibling);
     return;
   }
-  EXPECT_TRUE(file_set_authorized_root(root_fd, root_abs));
+  EXPECT_TRUE(utils_set_authorized_root(root_fd, root_abs));
 
   file_set_trust_sender(true);
   struct stat st;
@@ -1204,7 +1204,7 @@ static void test_trust_sender_authorized_root_confinement() {
 
   free(outside_link);
   free(inside_link);
-  file_set_authorized_root(-1, NULL);
+  utils_set_authorized_root(-1, NULL);
   close(root_fd);
   unlink("test_trust_sender_outside_link");
   rmdir(sibling);
@@ -1220,7 +1220,7 @@ void test_trust_sender() {
   test_trust_sender_confines_hostile_paths();
   test_trust_sender_authorized_root_confinement();
   file_set_trust_sender(false);
-  file_set_authorized_root(-1, NULL);
+  utils_set_authorized_root(-1, NULL);
 }
 
 /* --sparse/-S hole preservation: a buffer with a long zero run written via
@@ -1341,7 +1341,7 @@ static void test_file_write_to_disk_partial_retention() {
 static void test_dir_time_list() {
   const char* root = "test_dir_time_root";
   const char* sub = "test_dir_time_root/sub";
-  file_set_authorized_root(-1, NULL);
+  utils_set_authorized_root(-1, NULL);
   rmdir(sub);
   rmdir(root);
   EXPECT_EQ_INT(mkdir(root, 0755), 0);
@@ -1485,7 +1485,7 @@ static void test_keep_dirlinks_secure_open_impl() {
     rmdir(outside);
     return;
   }
-  EXPECT_TRUE(file_set_authorized_root(root_fd, root_abs));
+  EXPECT_TRUE(utils_set_authorized_root(root_fd, root_abs));
   file_set_keep_dirlinks(true);
 
   struct stat real_st;
@@ -1538,7 +1538,7 @@ static void test_keep_dirlinks_secure_open_impl() {
   free(leaf);
 
   file_set_keep_dirlinks(false);
-  file_set_authorized_root(-1, NULL);
+  utils_set_authorized_root(-1, NULL);
   close(root_fd);
   unlink(link);
   unlink(abslink);
@@ -1552,10 +1552,10 @@ static void test_keep_dirlinks_secure_open_impl() {
  * cleared even when an EXPECT inside the body returns early (a failing EXPECT
  * returns from its own function, so the body's trailing resets may be skipped). */
 static void test_keep_dirlinks_secure_open() {
-  file_set_authorized_root(-1, NULL);
+  utils_set_authorized_root(-1, NULL);
   file_set_keep_dirlinks(false);
   test_keep_dirlinks_secure_open_impl();
-  file_set_authorized_root(-1, NULL);
+  utils_set_authorized_root(-1, NULL);
   file_set_keep_dirlinks(false);
 }
 

tests/test_protocol.c

@@ -412,6 +412,87 @@ static void test_protocol_accounting_release_does_not_underflow() {
   protocol_session_unbind();
 }
 
+/* A Data acquired on session A must return its connection-memory charge to A
+   regardless of what (if anything) is bound at destroy time.  The original bug
+   had two halves: destroying A's Data while a different session is bound leaks
+   A and drains the bound session, and destroying it with nothing bound leaks A
+   and drains the legacy fallback session. */
+static void test_receive_data_charge_follows_owning_session() {
+  int pipe_a[2];
+  int pipe_b[2];
+  EXPECT_EQ_INT(pipe(pipe_a), 0);
+  EXPECT_EQ_INT(pipe(pipe_b), 0);
+
+  ProtocolSession session_a;
+  ProtocolSession session_b;
+  protocol_session_init(&session_a, pipe_a[0], pipe_a[1]);
+  protocol_session_init(&session_b, pipe_b[0], pipe_b[1]);
+  protocol_session_set_max_alloc(&session_a, 64);
+  protocol_session_set_max_alloc(&session_b, 64);
+
+  unsigned long long size = 8;
+  EXPECT_EQ_INT((int)write(pipe_a[1], &size, sizeof(size)), (int)sizeof(size));
+  EXPECT_EQ_INT((int)write(pipe_a[1], "12345678", 8), 8);
+  EXPECT_EQ_INT((int)write(pipe_a[1], &size, sizeof(size)), (int)sizeof(size));
+  EXPECT_EQ_INT((int)write(pipe_a[1], "ABCDEFGH", 8), 8);
+  EXPECT_EQ_INT((int)write(pipe_b[1], &size, sizeof(size)), (int)sizeof(size));
+  EXPECT_EQ_INT((int)write(pipe_b[1], "abcdefgh", 8), 8);
+
+  Data* data_a1 = protocol_receive_data_limited(&session_a, 8);
+  Data* data_a2 = protocol_receive_data_limited(&session_a, 8);
+  Data* data_b = protocol_receive_data_limited(&session_b, 8);
+  EXPECT_NOT_NULL(data_a1);
+  EXPECT_NOT_NULL(data_a2);
+  EXPECT_NOT_NULL(data_b);
+  EXPECT_TRUE(data_a1->owner == &session_a);
+  EXPECT_TRUE(data_a2->owner == &session_a);
+  EXPECT_TRUE(data_b->owner == &session_b);
+  EXPECT_EQ_INT((int)atomic_load(&session_a.total_allocated_bytes), 16);
+  EXPECT_EQ_INT((int)atomic_load(&session_b.total_allocated_bytes), 8);
+
+  /* Half 1: destroy A's Data while the unrelated session B is bound.  The
+     charge must go to A, not to the bound B. */
+  protocol_session_bind(&session_b);
+  data_destroy(data_a1);
+  protocol_session_unbind();
+
+  EXPECT_EQ_INT((int)atomic_load(&session_a.total_allocated_bytes), 8);
+  EXPECT_EQ_INT((int)atomic_load(&session_b.total_allocated_bytes), 8);
+
+  /* Half 2: destroy A's remaining Data with NO session bound.  The charge must
+     still go to A, not to the legacy fallback session. */
+  protocol_session_unbind();
+  data_destroy(data_a2);
+  EXPECT_EQ_INT((int)atomic_load(&session_a.total_allocated_bytes), 0);
+  EXPECT_EQ_INT((int)atomic_load(&session_b.total_allocated_bytes), 8);
+
+  data_destroy(data_b);
+  EXPECT_EQ_INT((int)atomic_load(&session_b.total_allocated_bytes), 0);
+
+  close(pipe_a[0]);
+  close(pipe_a[1]);
+  close(pipe_b[0]);
+  close(pipe_b[1]);
+}
+
+/* Freshest Data holds no connection charge; only a bounded receive binds an
+   owner and a charge, so creation helpers must start uncharged and unowned. */
+static void test_data_create_starts_uncharged_and_unowned() {
+  void* buf = malloc(8);
+  EXPECT_NOT_NULL(buf);
+  Data* created = data_create(buf, 8);
+  EXPECT_NOT_NULL(created);
+  EXPECT_TRUE(created->owner == NULL);
+  EXPECT_EQ_INT((int)created->protocol_charge, 0);
+  data_destroy(created);
+
+  Data* reserved = data_create_reserve(64);
+  EXPECT_NOT_NULL(reserved);
+  EXPECT_TRUE(reserved->owner == NULL);
+  EXPECT_EQ_INT((int)reserved->protocol_charge, 0);
+  data_destroy(reserved);
+}
+
 static void test_protocol_session_io_timeout() {
   /* Default is the built-in 60 s window; the setter stores exactly what it is
    * given (<= 0 means "fall back to the default") so callers can propagate
@@ -574,4 +655,6 @@ void test_protocol() {
   test_protocol_accounting_reservation_is_atomic();
   test_protocol_string_accounting_is_transient();
   test_protocol_accounting_release_does_not_underflow();
+  test_receive_data_charge_follows_owning_session();
+  test_data_create_starts_uncharged_and_unowned();
 }

tests/test_utils.h

@@ -112,4 +112,12 @@ extern bool current_test_failed;
     }                                                                                              \
   } while (0)
 
+/* Unconditional test failure carrying an explanatory message. */
+#define EXPECT_FAIL(message)                                                                       \
+  do {                                                                                             \
+    printf("    \033[1;31m[FAIL]\033[0m %s:%d: %s\n", __FILE__, __LINE__, (message));              \
+    current_test_failed = true;                                                                    \
+    return;                                                                                        \
+  } while (0)
+
 #endif