fix(followups): F5 - no test switch in the stall watcher

stall_watch read MAM_TEST_UNRELIABLE_AGENT to pretend an adapter's
agent_status was unreliable (PR #41 M7). The branch is gone. S13 now runs
the real stall_watch.main() in a process where the adapter itself reports
agent_status_reliable = False (_UNRELIABLE_MAIN), and checks the same
things as before: no idle notice or nudge, the blocked notice, and the
"idle judgement off" log line. A static check keeps MAM_TEST_ out of the
watcher (fails at 0051fd6). Without the seam S13 fails on this tree.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HCGpJXhSZasJLU38ksDghe

.agents/skills/lib_py/stall_watch.py

@@ -225,8 +225,6 @@ class StallWatch(object):
         name = resolve_agent(args.agent, args.target)
         adapter = get_adapter(name) if name else None
         reliable = bool(adapter.agent_status_reliable) if adapter else True
-        if os.environ.get("MAM_TEST_UNRELIABLE_AGENT") == args.agent:
-            reliable = False
         self.st = WatchState(idle_s=float(os.environ.get("MAM_STALL_IDLE_S", "600")), reliable=reliable)
         self.fail_s = float(os.environ.get("MAM_STALL_HERDR_FAIL_S", "120"))
         self.once = set()