feat: add pty monitoring

src/claude_code_api/backend.py

@@ -149,6 +149,18 @@ class ClaudeCodeBackend:
     def live_session_count(self) -> int:
         return len(self._sessions)
 
+    @property
+    def live_sessions(self) -> dict[str, PtyClaudeProcess]:
+        """Snapshot of live PTY processes keyed by ``session_id``.
+
+        Returned dict is a copy — caller may iterate freely without
+        worrying about concurrent ``complete()`` calls reshuffling
+        ``_sessions`` (which is keyed by history fingerprint, not
+        ``session_id``). Intended for debug surfaces (e.g. admin
+        terminal viewer) that need to look up a session by id.
+        """
+        return {s.session_id: s.pty for s in self._sessions.values()}
+
     async def complete(self, messages: list[Mapping[str, Any]]) -> AsyncIterator[Event]:
         """Run one turn against the matching session (or spawn one).
 

src/claude_code_api/pty.py

@@ -214,8 +214,14 @@ class PtyClaudeProcess:
         output_buffer_cap: int = _DEFAULT_OUTPUT_BUFFER_CAP,
     ) -> None:
         self._opts = options
-        self._on_output = on_pty_output
         self._output_buffer_cap = output_buffer_cap
+        # Listener list — drain thread fans out each chunk to every
+        # subscriber. Single-callback ``on_pty_output`` ctor arg is kept
+        # for compat; it just becomes the first listener.
+        self._output_listeners: list[PtyOutputCallback] = []
+        self._listeners_lock = threading.Lock()
+        if on_pty_output is not None:
+            self._output_listeners.append(on_pty_output)
 
         if options.resume_session_id is not None:
             self._session_id = options.resume_session_id
@@ -259,6 +265,22 @@ class PtyClaudeProcess:
         with self._output_lock:
             return bytes(self._output_buffer)
 
+    def add_output_listener(self, listener: PtyOutputCallback) -> None:
+        """Subscribe a callback to every chunk the drain thread reads.
+
+        Callbacks run on the drain thread; do as little as possible in
+        them (e.g. push to a queue) and never block. Exceptions are
+        swallowed per-listener to keep one bad subscriber from poisoning
+        the drain loop.
+        """
+        with self._listeners_lock:
+            self._output_listeners.append(listener)
+
+    def remove_output_listener(self, listener: PtyOutputCallback) -> None:
+        """Unsubscribe a previously added listener. Silent on missing."""
+        with self._listeners_lock, contextlib.suppress(ValueError):
+            self._output_listeners.remove(listener)
+
     async def start(self) -> None:
         """Spawn the child synchronously on the main thread.
 
@@ -333,8 +355,9 @@ class PtyClaudeProcess:
                 continue
             if not data:
                 break
-            cb = self._on_output
+            with self._listeners_lock:
-            if cb is not None:
+                listeners = list(self._output_listeners)
+            for cb in listeners:
                 with contextlib.suppress(Exception):
                     cb(data)
             with self._output_lock: