feat(issue-30): a stall watcher that only notifies

lib_py/stall_watch.py runs beside the wrapper's subscriber for a local herdr
job (started after delivery, stopped when the subscriber ends; MAM_STALL_WATCH=0
turns it off). It follows `herdr agent wait` transitions and publishes only
`progress` events through one publisher; it has no path that closes a job.

- blocked: `stalled:blocked <detection line>` once per episode, never answered.
- idle for MAM_STALL_IDLE_S (600) with no background descendants of the agent
  pid (pane process-info + /proc; adapter resident_children and the heartbeat
  timer excluded) and an empty input box: `stalled:idle` and one nudge.
- input box judged from adapter facts measured on herdr 0.9.1 (codex '›',
  grok frame '│', opencode '┃' block + stop pattern); the whole-pane fallback
  is gone. No facts: withheld + `stall_watch:input_check_unavailable` once;
  never empty for 3 x S: `stall_watch:input_never_empty` once.
- herdr failures are not "no event": warning + `stall_watch:herdr_unavailable:
  <code>` (or agent_not_found), backoff, rc 2 after MAM_STALL_HERDR_FAIL_S
  (120); the wrapper prints the watcher's last lines.
- remote and human jobs are skipped with one log line.
- agent_status_reliable is an adapter field; false turns idle judgement off.
- the loop runner relays stalled:/stall_watch: notices once each.
- scoped_env drops a pane-inherited workspace scope for name lookups (#34 rule).

The module sits at the top of lib_py: delegation and loop may not import the
agent adapters (their sibling-import rules). Idle pane captures of the five
CLIs are fixtures; the mock herdr answers process-info in the real shape.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.agents/skills/lib_py/agents/base.py

@@ -152,6 +152,34 @@ class BaseAgentAdapter:
     def input_rule_pattern(self) -> Optional[str]:
         return None
 
+    @property
+    def input_frame_chars(self) -> str:
+        """Box-border characters stripped from both ends of an input line (#30)."""
+        return ''
+
+    @property
+    def input_block_prefix(self) -> Optional[str]:
+        """Line prefix of an input box drawn as a block instead of between rules (#30)."""
+        return None
+
+    @property
+    def input_stop_pattern(self) -> Optional[str]:
+        """Regex of the status line that ends the input area inside such a block (#30)."""
+        return None
+
+    @property
+    def resident_children(self) -> tuple:
+        """Process names this CLI keeps as children while idle (#30). The stall
+        watcher does not count them as background work."""
+        return ()
+
+    @property
+    def agent_status_reliable(self) -> bool:
+        """Whether herdr's agent_status for this CLI can drive the idle judgement
+        (#30). On herdr 0.9.1 claude, agy, grok, opencode and codex all report
+        working/idle transitions; a False here turns the idle nudge off."""
+        return True
+
     @property
     def modal_tokens(self) -> Optional[str]:
         return None