log_tail: add log_dir + log_pattern directory-watch mode

Valve games (TF2, GMod) rotate into a new timestamped log file on every
map change. The existing fixed-path inotify watch goes stale after the
first rotation. This adds a directory-watch mode that auto-switches to
the newest matching file whenever one appears.

New YAML fields (mutually exclusive with logs:):
  log_dir:     directory to watch for new log files
  log_pattern: fnmatch(3) glob for filenames; default "*"

Changes:
- umbrella.h: add log_dir[MAX_PATH] and log_dir_pattern[MAX_PATH] to Unit
- log_tail.c: extend LogWatch with dir_wd/dir_path/pattern fields;
  add log_tail_drain, log_tail_scan_dir, log_tail_switch_file,
  log_tail_open_fixed_watch, log_tail_open_dir_watch,
  log_tail_reopen_fixed, log_tail_handle_rotation_dir;
  refactor log_tail_init, log_tail_handle, log_tail_cleanup
- unit.c: parse log_dir and log_pattern YAML keys; warn and drop logs:
  if both are set on the same unit
- AGENTS.md, README.md: document both log-tail modes

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

1 files changed, 11 insertions, 0 deletions

diff --git a/src/unit.c b/src/unit.c
index b2cdd4c..1b4a603 100644
--- a/src/unit.c
+++ b/src/unit.c
@@ -176,6 +176,10 @@ int unit_load_file(const char *path, Unit *out) {
                         strncpy(out->broadcast_cmd, val, sizeof(out->broadcast_cmd) - 1);
                     else if (strcmp(last_key, "log_filter") == 0)
                         strncpy(out->log_filter, val, MAX_PATH - 1);
+                    else if (strcmp(last_key, "log_dir") == 0)
+                        strncpy(out->log_dir, val, MAX_PATH - 1);
+                    else if (strcmp(last_key, "log_pattern") == 0)
+                        strncpy(out->log_dir_pattern, val, MAX_PATH - 1);
                     break;
 
                 case SECTION_CONSOLE:
@@ -261,6 +265,13 @@ int unit_load_file(const char *path, Unit *out) {
                      out->name, out->console.password_env);
     }
 
+    /* log_dir and logs: are mutually exclusive */
+    if (out->log_dir[0] && out->log_count > 0) {
+        log_warn("Unit %s: 'log_dir' and 'logs' are mutually exclusive; "
+                 "ignoring 'logs'", out->name);
+        out->log_count = 0;
+    }
+
     /* Allocate ring buffer */
     out->output = ring_init();
     if (!out->output) {