fix: reject unsupported rsync client stderr mode

RSYNC_COMPAT.md

@@ -6,11 +6,11 @@ This document maps rsync's full feature set to FastSync's current implementation
 
 | Status | Count | Description |
 |--------|-------|-------------|
-| ✅ Implemented | 34 | Feature works end-to-end |
-| 🔀 Alt Arg | 3 | Functionality exists but under different flag/semantics |
-| ⚠️ Partial | 1 | Flag parsed/stored but behavior incomplete |
-| ❌ Not Implemented | 98 | Flag not recognized or no behavior |
-| **Total** | **136** | |
+| ✅ Implemented | 35 | Feature works end-to-end |
+| 🔀 Alt Arg | 4 | Functionality exists but under different flag/semantics |
+| ⚠️ Partial | 5 | Flag parsed/stored but behavior incomplete |
+| ❌ Not Implemented | 97 | Flag not recognized or no behavior |
+| **Total** | **141** | |
 
 ---
 
@@ -25,7 +25,7 @@ This document maps rsync's full feature set to FastSync's current implementation
 | `-V`, `--version` | Print version | ✅ Implemented | |
 | `--info=FLAGS` | Fine-grained info verbosity | ❌ Not Implemented | Removed because it had no effect |
 | `--debug=FLAGS` | Fine-grained debug verbosity | ❌ Not Implemented | Removed because it had no effect |
-| `--stderr=MODE` | Change stderr output mode | ⚠️ Partial | `errors` (default), `all`, and `client` are accepted; `client` preserves local client routing because FastSync has no rsync message channel |
+| `--stderr=MODE` | Change stderr output mode | ⚠️ Partial | `errors` (default) and `all` are supported; `client` is rejected because FastSync has no rsync message channel |
 | `--no-motd` | Suppress daemon MOTD | ❌ Not Implemented | |
 | `--exclude=PATTERN` | Exclude files matching pattern | ✅ Implemented | Glob matching in scanner |
 | `--include=PATTERN` | Include files matching pattern | ✅ Implemented | Glob matching in scanner |

src/client/client_cli.c

@@ -91,10 +91,12 @@ static int set_stderr_mode(const char* value) {
     log_set_stderr_mode(LOG_STDERR_ERRORS);
   else if (strcmp(value, "all") == 0 || strcmp(value, "a") == 0)
     log_set_stderr_mode(LOG_STDERR_ALL);
-  else if (strcmp(value, "client") == 0 || strcmp(value, "c") == 0)
-    log_set_stderr_mode(LOG_STDERR_CLIENT);
-  else {
-    log_message(LOG_LEVEL_ERROR, "--stderr must be errors, all, or client");
+  else if (strcmp(value, "client") == 0 || strcmp(value, "c") == 0) {
+    log_message(LOG_LEVEL_ERROR,
+                "--stderr=client is not supported: FastSync has no client message channel");
+    return -1;
+  } else {
+    log_message(LOG_LEVEL_ERROR, "--stderr must be errors or all");
     return -1;
   }
   return 0;

src/client/usage.c

@@ -58,7 +58,7 @@ void print_usage(void) {
   printf("  --stats             Print transfer statistics at end\n");
   printf("  --max-depth <n>     Maximum directory depth (0=unlimited)\n");
   printf("  --log-file <path>   Write log messages to file\n");
-  printf("  --stderr=MODE       Route logging to stderr: errors, all, or client\n");
+  printf("  --stderr=MODE       Route logging to stderr: errors or all\n");
   printf("  --partial           Keep partial files on interrupted transfer\n");
   printf("  --partial-dir <dir> Directory for partial files\n");
   printf("  --fastsync-server-path <path>\n");

src/shared/log.h

@@ -4,7 +4,7 @@
 #include <stdio.h>
 
 typedef enum { LOG_LEVEL_DEBUG, LOG_LEVEL_INFO, LOG_LEVEL_WARNING, LOG_LEVEL_ERROR } LogLevel;
-typedef enum { LOG_STDERR_ERRORS, LOG_STDERR_ALL, LOG_STDERR_CLIENT } LogStderrMode;
+typedef enum { LOG_STDERR_ERRORS, LOG_STDERR_ALL } LogStderrMode;
 
 void log_message(LogLevel log_level, const char* message, ...);
 void log_perror(const char* context);

tests/test_client_cli.c

@@ -341,9 +341,9 @@ static void test_parse_args_archive() {
 }
 
 static void test_parse_args_stderr_modes() {
-  static const char* const modes[] = {"errors", "all", "client", "e", "a", "c"};
-  static const LogStderrMode expected[] = {LOG_STDERR_ERRORS, LOG_STDERR_ALL, LOG_STDERR_CLIENT,
-                                           LOG_STDERR_ERRORS, LOG_STDERR_ALL, LOG_STDERR_CLIENT};
+  static const char* const modes[] = {"errors", "all", "e", "a"};
+  static const LogStderrMode expected[] = {LOG_STDERR_ERRORS, LOG_STDERR_ALL, LOG_STDERR_ERRORS,
+                                           LOG_STDERR_ALL};
   for (size_t i = 0; i < sizeof(modes) / sizeof(modes[0]); i++) {
     Config* cfg = config_create();
     char option[32];
@@ -358,13 +358,18 @@ static void test_parse_args_stderr_modes() {
   log_set_stderr_mode(LOG_STDERR_ERRORS);
 }
 
-static void test_parse_args_rejects_invalid_stderr_mode() {
-  Config* cfg = config_create();
-  char* argv[] = {"fastsync", "--stderr=invalid", "/src", "/dst"};
-  int positional_args[2];
-  int positional_count = 0;
-  EXPECT_EQ_INT(parse_args(cfg, 4, argv, positional_args, &positional_count), -1);
-  config_delete(cfg);
+static void test_parse_args_rejects_unsupported_stderr_modes() {
+  static const char* const modes[] = {"client", "c", "invalid"};
+  for (size_t i = 0; i < sizeof(modes) / sizeof(modes[0]); i++) {
+    Config* cfg = config_create();
+    char option[32];
+    snprintf(option, sizeof(option), "--stderr=%s", modes[i]);
+    char* argv[] = {"fastsync", option, "/src", "/dst"};
+    int positional_args[2];
+    int positional_count = 0;
+    EXPECT_EQ_INT(parse_args(cfg, 4, argv, positional_args, &positional_count), -1);
+    config_delete(cfg);
+  }
   log_set_stderr_mode(LOG_STDERR_ERRORS);
 }
 
@@ -390,5 +395,5 @@ void test_client_cli() {
   test_parse_args_rejects_unimplemented_options();
   test_parse_args_archive();
   test_parse_args_stderr_modes();
-  test_parse_args_rejects_invalid_stderr_mode();
+  test_parse_args_rejects_unsupported_stderr_modes();
 }