feat: add --files-from/-0, --filter, -C and -F filter layer

Implement the RSYNC_COMPAT Phase-2 filter/parser feature group:
- --files-from=FILE (repeatable) plus -0/--from0 NUL delimiters: parse the
  source file list relative to the source root into a shared read-only
  allow-set; the scanner transfers listed files and the whole subtree of
  listed directories and prunes everything else in single- and
  multithreaded mode. Absolute/'..' entries and missing files are hard
  CLI errors.
- --filter=RULE: rsync-style +/- rules (anchored '/', dir-only trailing '/',
  word include/exclude forms) evaluated first-match-wins with a default of
  include, as an independent layer from legacy --exclude/--include.
  Unsupported directives (merge/hide/... ) are rejected explicitly. -f stays
  sendfile.
- -C/--cvs-exclude: well-known rsync CVS default exclude set.
- -F: per-directory .rsync-filter files read during traversal and applied to
  the owning directory's subtree (single + parallel), never transferred.
- Delete manifest still derives from what was actually sent.

Client-only config fields; no wire/protocol change. Adds unit coverage
(CLI parse, allow-set and filter scanning single+parallel) and integration
tests (TestFilesFrom, TestFilters). RSYNC_COMPAT matrix rows updated:
5 rows move to Implemented (Summary 62/3/5/1/76 = 147).

src/shared/file_list.c

@@ -0,0 +1,188 @@
+#include "file_list.h"
+#include "log.h"
+#include "utils.h"
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+typedef struct {
+  char** items;
+  int count;
+  int capacity;
+} StringList;
+
+static void string_list_destroy(StringList* list) {
+  if (!list)
+    return;
+  for (int i = 0; i < list->count; i++)
+    free(list->items[i]);
+  free(list->items);
+}
+
+static bool string_list_add(StringList* list, const char* text) {
+  if (list->count == list->capacity) {
+    int new_cap = list->capacity > 0 ? list->capacity * 2 : 16;
+    char** grown = realloc(list->items, (size_t)new_cap * sizeof(char*));
+    if (!grown)
+      return false;
+    list->items = grown;
+    list->capacity = new_cap;
+  }
+  list->items[list->count] = str_dup(text);
+  if (!list->items[list->count])
+    return false;
+  list->count++;
+  return true;
+}
+
+/* Validate and normalize one entry. Returns:
+ *   1 -> added to `out`
+ *   0 -> blank entry, skip
+ *  -1 -> invalid (message set in `err`) */
+static int normalize_entry(const char* raw, size_t len, StringList* out, char* err,
+                           size_t err_size) {
+  /* Trim the trailing newline/carriage-return from line mode. */
+  while (len > 0 && (raw[len - 1] == '\n' || raw[len - 1] == '\r'))
+    len--;
+  if (len == 0)
+    return 0;
+  if (raw[0] == '/') {
+    snprintf(err, err_size, "absolute path entries are not allowed: '%s'", raw);
+    return -1;
+  }
+  /* Reject NUL bytes inside a token defensively (NUL-delimited mode splits on
+   * them, so this only guards against embedded garbage). */
+  char* dup = malloc(len + 1);
+  if (!dup) {
+    snprintf(err, err_size, "memory allocation failed");
+    return -1;
+  }
+  memcpy(dup, raw, len);
+  dup[len] = '\0';
+
+  /* Rebuild the path token-by-token: skip '.' and empty segments, reject '..'. */
+  size_t out_len = 0;
+  for (const char* part = dup;;) {
+    const char* slash = strchr(part, '/');
+    size_t part_len = slash ? (size_t)(slash - part) : strlen(part);
+    if (part_len == 1 && part[0] == '.') {
+      /* skip "." segment */
+    } else if (part_len == 2 && part[0] == '.' && part[1] == '.') {
+      snprintf(err, err_size, "path traversal entry is not allowed: '%s'", dup);
+      free(dup);
+      return -1;
+    } else if (part_len > 0) {
+      if (out_len > 0)
+        dup[out_len++] = '/';
+      memmove(dup + out_len, part, part_len);
+      out_len += part_len;
+    }
+    if (!slash)
+      break;
+    part = slash + 1;
+  }
+  dup[out_len] = '\0';
+
+  int result;
+  if (out_len == 0) {
+    /* "." / "./" lists the source root: the whole tree is transferred. */
+    result = string_list_add(out, "") ? 1 : -1;
+    if (result < 0)
+      snprintf(err, err_size, "memory allocation failed");
+  } else {
+    result = string_list_add(out, dup) ? 1 : -1;
+    if (result < 0)
+      snprintf(err, err_size, "memory allocation failed");
+  }
+  free(dup);
+  return result;
+}
+
+static FileListSet* string_list_to_set(StringList* raw, char* err, size_t err_size) {
+  FileListSet* set = malloc(sizeof(FileListSet));
+  if (!set) {
+    snprintf(err, err_size, "memory allocation failed");
+    return NULL;
+  }
+  set->count = raw->count;
+  set->entries = raw->items;
+  raw->items = NULL;
+  raw->count = 0;
+  return set;
+}
+
+FileListSet* file_list_load(const char* path, bool null_separated, char* err, size_t err_size) {
+  if (err && err_size > 0)
+    err[0] = '\0';
+  if (!path || !*path) {
+    snprintf(err, err_size, "no file given");
+    return NULL;
+  }
+  FILE* fp = fopen(path, "r");
+  if (!fp) {
+    char* escaped = output_escape(path, false);
+    snprintf(err, err_size, "could not open '%s': %s", escaped ? escaped : path, strerror(errno));
+    free(escaped);
+    return NULL;
+  }
+
+  StringList raw = {0};
+  char* line = NULL;
+  size_t line_cap = 0;
+  ssize_t n;
+  bool ok = true;
+  char delim = null_separated ? '\0' : '\n';
+  while (ok && (n = getdelim(&line, &line_cap, delim, fp)) != -1) {
+    int r = normalize_entry(line, (size_t)n, &raw, err, err_size);
+    if (r < 0) {
+      ok = false;
+      break;
+    }
+  }
+  free(line);
+  fclose(fp);
+  if (!ok) {
+    string_list_destroy(&raw);
+    return NULL;
+  }
+  FileListSet* set = string_list_to_set(&raw, err, err_size);
+  if (!set)
+    string_list_destroy(&raw);
+  return set;
+}
+
+void file_list_destroy(FileListSet* set) {
+  if (!set)
+    return;
+  for (int i = 0; i < set->count; i++)
+    free(set->entries[i]);
+  free(set->entries);
+  free(set);
+}
+
+static bool path_has_prefix(const char* path, const char* prefix) {
+  size_t plen = strlen(prefix);
+  if (strncmp(path, prefix, plen) != 0)
+    return false;
+  return path[plen] == '/' || path[plen] == '\0';
+}
+
+bool file_list_affects(const FileListSet* set, const char* rel) {
+  if (!set)
+    return true;
+  if (!rel)
+    return false;
+  for (int i = 0; i < set->count; i++) {
+    const char* entry = set->entries[i];
+    if (entry[0] == '\0')
+      return true; /* whole tree listed */
+    if (strcmp(rel, entry) == 0)
+      return true; /* the entry itself is listed */
+    if (path_has_prefix(rel, entry))
+      return true; /* rel lives under a listed directory */
+    if (path_has_prefix(entry, rel))
+      return true; /* rel is an ancestor directory of a listed entry */
+  }
+  return false;
+}