fix(issue-19): close the trap race, select daemons by argv shape, align docs with the polling fallback

Review round 1 (claude PASS, agy PASS) recommendations:
- reconcile.sh: `_sub_stop` falls back to `$!` for the window before
  `_sub_pid=$!` (R-1); lock identity compared as (st_dev, st_ino).
- lib.sh legacy start_watchdog prints nothing when opted out and no daemon
  runs, byte-identical to the python body.
- conftest/test: `_is_subscriber_daemon_argv` selects only
  `bash|sh <root>/.../reconcile.sh --subscribe`, never a brief-carrying
  wrapper that quotes the words or a prefix-colliding sibling root (R-2);
  one new unit test for the selector.
- monitor SKILL.md / VERSIONS.md: the polling fallback checks the lock
  file's presence only and does not exclude a second daemon; measurement
  wording uses the argv-shape criterion instead of raw pgrep.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VCgu9Fa9iT7TbJUSzdq4Ff

tests/conftest.py

@@ -29,6 +29,23 @@ SKILLS_DIR = str(Path(__file__).resolve().parent.parent / ".agents" / "skills")
 if SKILLS_DIR not in sys.path:
     sys.path.insert(0, SKILLS_DIR)
 
+def _is_subscriber_daemon_argv(args, root):
+    """True only for the daemon's own command line: `bash|sh <root>/.../reconcile.sh
+    --subscribe ...`. A process that merely *quotes* those words (a loop driver
+    or delegate wrapper carrying a brief in argv) and a sibling root that is a
+    string prefix of `root` (`.../pytest-9` vs `.../pytest-99`) are excluded
+    (review R-2) - the reaper kills what it selects."""
+    argv = args.split()
+    if len(argv) < 3:
+        return False
+    if os.path.basename(argv[0]) not in ("bash", "sh"):
+        return False
+    script = argv[1]
+    return (script.startswith(str(root).rstrip(os.sep) + os.sep)
+            and script.endswith(os.sep + "reconcile.sh")
+            and argv[2] == "--subscribe")
+
+
 def _subscriber_daemon_pids(root):
     """PIDs of `reconcile.sh --subscribe` daemons whose command line lives under
     `root`, plus their children (the python subscriber the bash wrapper waits on).
@@ -40,7 +57,7 @@ def _subscriber_daemon_pids(root):
     root = str(root)
     found = []
     for pid in _run_real(["pgrep", "-f", "reconcile.sh --subscribe"]).split():
-        if root in _run_real(["ps", "-o", "args=", "-p", pid]):
+        if _is_subscriber_daemon_argv(_run_real(["ps", "-o", "args=", "-p", pid]), root):
             found.append(int(pid))
     kids = []
     for pid in found: