fix(tui): autonomous background process completion notifications (#26071) (#26327)

* feat(process-registry): add format_process_notification shared helper

* feat(process-registry): add drain_notifications method

* refactor(cli): use shared drain_notifications and format_process_notification

* feat(tui): add background notification poller for completion_queue

* feat(tui): wire notification poller into session init/finalize

* refactor(tui): add post-turn drain using shared helper as safety net

tools/process_registry.py

@@ -826,6 +826,26 @@ class ProcessRegistry:
         """Check if a completion notification was already consumed via wait/poll/log."""
         return session_id in self._completion_consumed
 
+    def drain_notifications(self) -> "list[tuple[dict, str]]":
+        """Pop all pending notification events and return formatted pairs.
+
+        Returns a list of (raw_event, formatted_text) tuples.
+        Skips completion events that were already consumed via wait/poll/log.
+        """
+        results = []
+        while not self.completion_queue.empty():
+            try:
+                evt = self.completion_queue.get_nowait()
+            except Exception:
+                break
+            _evt_sid = evt.get("session_id", "")
+            if evt.get("type") == "completion" and self.is_completion_consumed(_evt_sid):
+                continue
+            text = format_process_notification(evt)
+            if text:
+                results.append((evt, text))
+        return results
+
     def get(self, session_id: str) -> Optional[ProcessSession]:
         """Get a session by ID (running or finished)."""
         with self._lock:
@@ -1388,6 +1408,44 @@ class ProcessRegistry:
 process_registry = ProcessRegistry()
 
 
+def format_process_notification(evt: dict) -> "str | None":
+    """Format a process notification event into a [IMPORTANT: ...] message.
+
+    Handles completion events (notify_on_complete), watch pattern matches,
+    and watch disabled events from the unified completion_queue.
+    """
+    evt_type = evt.get("type", "completion")
+    _sid = evt.get("session_id", "unknown")
+    _cmd = evt.get("command", "unknown")
+
+    if evt_type == "watch_disabled":
+        return f"[IMPORTANT: {evt.get('message', '')}]"
+
+    if evt_type == "watch_match":
+        _pat = evt.get("pattern", "?")
+        _out = evt.get("output", "")
+        _sup = evt.get("suppressed", 0)
+        text = (
+            f"[IMPORTANT: Background process {_sid} matched "
+            f"watch pattern \"{_pat}\".\n"
+            f"Command: {_cmd}\n"
+            f"Matched output:\n{_out}"
+        )
+        if _sup:
+            text += f"\n({_sup} earlier matches were suppressed by rate limit)"
+        text += "]"
+        return text
+
+    _exit = evt.get("exit_code", "?")
+    _out = evt.get("output", "")
+    return (
+        f"[IMPORTANT: Background process {_sid} completed "
+        f"(exit code {_exit}).\n"
+        f"Command: {_cmd}\n"
+        f"Output:\n{_out}]"
+    )
+
+
 # ---------------------------------------------------------------------------
 # Registry -- the "process" tool schema + handler
 # ---------------------------------------------------------------------------