WebSocket Protocol

Full protocol reference for the streaming agent interface. File: navi/api/websocket.py.

Connection

ws://host/ws/sessions/{session_id}

The session must exist before connecting (create via POST /sessions). If the session is not found, the WebSocket closes with code 4004.

On connect the server immediately sends either session_sync (no active run) or begins the reconnect flow (active run detected).

Messages: client → server

{
    "type": "message",
    "content": "user text",
    "images": ["base64string", ...],
    "files": [{"name": "file.pdf", "path": "/abs/path"}]
}

• type must be "message". Other types return an error frame.
• content is required and must be non-empty.
• images: optional list of base64-encoded images (data URIs accepted; the data:...;base64, prefix is stripped server-side).
• files: optional list of uploaded file references (appended to content as [Uploaded files on disk: ...]).

Messages: server → client

All frames are JSON objects with a type field.

Stream lifecycle

Thinking (reasoning)

Thinking blocks are collapsible in the UI: open during reasoning, auto-collapsed on thinking_end.

Planning

planning_status frames arrive during each planning phase (analysis → optional reflect → plan). is_subagent: true means the planning is running inside a subagent — route it into the spawn_agent card, never into the top-level UI.

plan_ready carries the formatted step list. Rendered as a collapsible plan card in the UI.

Tool calls

is_subagent: true indicates the tool call was made by a nested subagent, not the top-level agent.

Text output

Other events

session_sync is sent in two situations:

1. On fresh connect when no run is active — in case the agent finished while the client was disconnected.
2. After a reconnect-and-replay completes — to ensure the client sees the fully saved response.

Stopping generation

POST /sessions/{session_id}/stop

Sets _AgentRun.stop_event. The agent checks this event:

• Before each LLM call
• During streaming (breaks out, calls aclose() on the generator)
• After tool execution

The client sends this via fetch(), not over the WebSocket, to avoid corrupting the WebSocket receive state.

Response: {"ok": true} if a run was active, {"ok": false, "reason": "no active run"} otherwise.

Reconnection

If the client reconnects to an in-progress run (e.g. page reload mid-stream), websocket_session() detects the existing _AgentRun in _runs and replays the full event buffer before routing live events:

← stream_start
← replay_start   {"type": "replay_start", "count": N}
← ev_0 ... ev_N  (all buffered events replayed verbatim)
← replay_end     {"type": "replay_end"}
← (live events continue from here)
...
← session_sync   (after stream finishes — sync final saved state)

The client should suppress cursor animations and other in-progress effects while replay_start..replay_end is in flight.

If the client reconnects after the run has already finished, there is no active _AgentRun, so it receives only session_sync and must fetch history via REST.

Run state management

_runs: dict[str, _AgentRun] — global dict of active runs, keyed by session ID.

_AgentRun holds:

• task: asyncio.Task — the running agent task
• stop_event: asyncio.Event — cooperative stop signal
• subscribers: list[Queue] — one queue per connected WebSocket client
• events: list[dict] — replay buffer; every serialised event dict emitted this turn

Events are broadcast to all subscribers and appended to events. When the run finishes, _runs.pop(session_id) is called from the finally block. The subscribe-then-note-count ordering guarantees no events are missed between the two steps (single-threaded async Python).