Live agent todo list: compact scrollable strip above the composer

Add a todo.update frame (server->app) carrying the agent's full current
todo list. The gateway emits it whenever the hermes todo tool completes
(the tool result is authoritative even for merge writes) and re-sends a
snapshot right after hello so a reconnecting device re-learns the plan.
Ephemeral: never outboxed.

The app renders it as a compact strip above the composer (max 3 lines,
the rest scrollable) mirroring the hermes desktop composer status stack:
pending = hollow ring, in_progress = spinner, completed = green check,
cancelled = struck through. It auto-scrolls to the current task whenever
the active task changes, and hides itself once the list is empty or fully
resolved.

gateway-plugin/protocol.py

@@ -48,6 +48,9 @@ TYPE_TOOL_START = "tool.start"
 TYPE_TOOL_PROGRESS = "tool.progress"
 TYPE_TOOL_END = "tool.end"
 
+# Agent todo list (live planning state; ephemeral, never outboxed)
+TYPE_TODO_UPDATE = "todo.update"
+
 # Intermediate assistant beat (M2)
 TYPE_COMMENTARY = "commentary"
 
@@ -486,6 +489,35 @@ def tool_end(
     )
 
 
+# ---------------------------------------------------------------------------
+# Todo-update frame (agent planning state)
+# ---------------------------------------------------------------------------
+
+
+def todo_update(
+    chat_id: str,
+    todos: list[dict[str, str]],
+    *,
+    thread_id: str | None = None,
+) -> Frame:
+    """The agent's current todo list for a chat/thread lane.
+
+    Emitted whenever the ``todo`` tool completes (the tool result is the
+    authoritative full list — it also covers ``merge`` writes, whose args
+    carry only the changed items) and, as a snapshot, when a device opens
+    its event stream. Ephemeral state: never outboxed, so a reconnecting
+    device learns the current list from the snapshot instead of a replay.
+    Each item is ``{id, content, status}`` with status one of
+    ``pending | in_progress | completed | cancelled``.
+    """
+    return Frame(
+        type=TYPE_TODO_UPDATE,
+        chat_id=chat_id,
+        thread_id=thread_id,
+        payload={"todos": todos},
+    )
+
+
 # ---------------------------------------------------------------------------
 # Commentary frame (M2)
 # ---------------------------------------------------------------------------