fix: filter precedence, files-from errors, NUL/CRLF and filter-rule rejections

Address an independent c-review of the files-from/filter feature:

- .rsync-filter precedence now matches rsync: evaluate the innermost
  (current) directory's rules first, then ancestors, then the command-line
  base (--filter/-C), so a deeper file's '+' can re-include what a shallower
  '-' excluded (regression tests in both scan modes; single-thread and -m).
- --files-from: a listed entry missing on disk and an empty list are now hard
  errors surfaced pre-transfer in send_files, send_files_multithreaded,
  dry-run and --list-only; '.' (whole tree) and empty listed dirs stay valid.
- scanner_path_relative now handles a transfer root of / (previously the
  scanner aborted on children of /).
- Reject unsupported rsync filter syntax explicitly (no silent no-ops):
  +/- modifiers other than '/' (! C s r p x) and rules beginning with ':'/'.'
  /'!' (merge/dir-merge/list-clear shorthands). Docs updated.
- -0/--from0 NUL mode preserves entry bytes (no CR/LF trimming); only newline
  mode trims. Absolute-entry error message no longer includes the newline.
- --no-from0/--no-cvs-exclude registered as negatable booleans.
- RSYNC_COMPAT rows updated for the precedence, rejection list, NUL-mode
  detail and the documented O(entries x files) scalability bound of the
  allow-set (Summary unchanged: 62/3/5/1/76 = 147).

tests/test_client_cli.c

@@ -1289,6 +1289,29 @@ static void test_parse_args_filter_rules() {
   char* missing_argv[] = {"fastsync", "/src", "/dst", "--filter"};
   EXPECT_EQ_INT(parse_args(cfg, 4, missing_argv, positional_args, &positional_count), -1);
   config_delete(cfg);
+
+  /* rsync shorthands/modifiers we do not support are rejected instead of being
+   * silently parsed as literal patterns. */
+  static const char* const unsupported[] = {
+      ": .rsync-filter", ". /tmp/rules", "-s foo", "-p bar", "-C", "-! *.o", "!",
+  };
+  for (size_t i = 0; i < sizeof(unsupported) / sizeof(unsupported[0]); i++) {
+    cfg = config_create();
+    positional_count = 0;
+    char* rule_argv[] = {"fastsync", "--filter", (char*)unsupported[i], "/src", "/dst"};
+    EXPECT_EQ_INT(parse_args(cfg, 5, rule_argv, positional_args, &positional_count), -1);
+    config_delete(cfg);
+  }
+
+  /* Supported spellings still parse: space- or slash-separated, attached
+   * wildcards, and anchored rules. */
+  cfg = config_create();
+  positional_count = 0;
+  char* ok_argv[] = {"fastsync",         "--filter=-*.o", "--filter=- /foo",
+                     "--filter=+ /bar/", "/src",          "/dst"};
+  EXPECT_EQ_INT(parse_args(cfg, 6, ok_argv, positional_args, &positional_count), 0);
+  EXPECT_EQ_INT(cfg->filters->size, 3);
+  config_delete(cfg);
 }
 
 /* -0/--from0, -C/--cvs-exclude and -F wire into their config flags. */
@@ -1316,6 +1339,19 @@ static void test_parse_args_from0_cvs_filter_file_flags() {
     EXPECT_EQ_INT(cfg->per_dir_filter, cases[i].per_dir);
     config_delete(cfg);
   }
+
+  /* The plain booleans are negatable (--no-* simply clears the flag). */
+  static const char* const on[][2] = {{"--from0", "--no-from0"}, {"-C", "--no-cvs-exclude"}};
+  for (size_t i = 0; i < sizeof(on) / sizeof(on[0]); i++) {
+    Config* cfg = config_create();
+    int positional_args[2];
+    int positional_count = 0;
+    char* argv[] = {"fastsync", (char*)on[i][0], (char*)on[i][1], "/src", "/dst"};
+    EXPECT_EQ_INT(parse_args(cfg, 5, argv, positional_args, &positional_count), 0);
+    EXPECT_FALSE(cfg->from0);
+    EXPECT_FALSE(cfg->cvs_exclude);
+    config_delete(cfg);
+  }
 }
 
 static void write_file_bytes(const char* path, const char* bytes, size_t len) {
@@ -1347,7 +1383,8 @@ static void test_parse_args_files_from() {
   config_delete(cfg);
   remove(list_path);
 
-  /* -0 switches the separator to NUL regardless of argument order. */
+  /* -0 switches the separator to NUL regardless of argument order, and NUL
+   * mode preserves entry bytes exactly (a trailing CR/LF is part of the name). */
   write_file_bytes(list_path, "x.txt\0y/z.bin\0", 14);
   cfg = config_create();
   positional_count = 0;
@@ -1365,6 +1402,21 @@ static void test_parse_args_files_from() {
   config_delete(cfg);
   remove(list_path);
 
+  write_file_bytes(list_path, "crlf\n\0tail\0", 11);
+  cfg = config_create();
+  positional_count = 0;
+  char* nul_nl_argv[] = {"fastsync",
+                         "--files-from="
+                         "cli_files_from_list.txt",
+                         "-0", "/src", "/dst"};
+  EXPECT_EQ_INT(parse_args(cfg, 5, nul_nl_argv, positional_args, &positional_count), 0);
+  set = (FileListSet*)cfg->files_from_set;
+  EXPECT_NOT_NULL(set);
+  EXPECT_TRUE(file_list_affects(set, "crlf\n"));
+  EXPECT_TRUE(file_list_affects(set, "tail"));
+  config_delete(cfg);
+  remove(list_path);
+
   /* A missing list file is a hard parse-time error. */
   cfg = config_create();
   positional_count = 0;