Reasoning now flows as its own stream — symmetric to the answer's
``delta`` / ``stream_end`` pair — instead of being shipped as one
oversized progress message. This lets WebUI render a live "Thinking…"
bubble that updates in place, then auto-collapses when the stream
closes. Other channels remain plugin no-ops by default.
## Protocol
New metadata: ``_reasoning_delta`` (chunk) and ``_reasoning_end``
(close marker). ChannelManager routes both to the dedicated plugin
hooks below; the legacy one-shot ``_reasoning`` is kept for back-compat
and BaseChannel expands it into a single delta + end pair so plugins
only ever implement the streaming primitives.
WebSocket emits two new events:
- ``reasoning_delta`` (event, chat_id, text, optional stream_id)
- ``reasoning_end`` (event, chat_id, optional stream_id)
## BaseChannel surface
- ``send_reasoning_delta(chat_id, delta, metadata)`` — no-op default
- ``send_reasoning_end(chat_id, metadata)`` — no-op default
- ``send_reasoning(msg)`` — back-compat wrapper, base impl forwards
to the streaming primitives
A channel adds reasoning support by overriding the two streaming
primitives. Telegram / Slack / Discord / Feishu / WeChat / Matrix keep
the base no-ops until their bubble UIs are adapted; reasoning silently
drops at dispatch, never as a stray text message.
## AgentHook
Adds ``emit_reasoning_end`` to the hook lifecycle. ``_LoopHook`` tracks
whether a reasoning segment is open and closes it on:
- the first answer delta arriving (so the UI locks the bubble before
the answer renders below),
- ``on_stream_end``,
- one-shot ``reasoning_content`` / ``thinking_blocks`` after a single
non-streaming response.
## WebUI
- ``UIMessage.reasoning`` is now a single accumulated string with a
companion ``reasoningStreaming`` flag.
- ``useNanobotStream`` consumes ``reasoning_delta`` / ``reasoning_end``;
legacy ``kind: "reasoning"`` is auto-translated to a delta + end.
- New ``ReasoningBubble``: shimmer header + auto-expanded while
streaming, collapses to a clickable "Thinking" pill once closed,
respects ``prefers-reduced-motion``.
- Answer deltas adopt the reasoning placeholder so the bubble and the
answer share one assistant row.
## Tests
- ``tests/channels/test_channel_manager_reasoning.py`` — manager routes
delta + end, drops on channel opt-out, expands one-shot back-compat.
- ``tests/channels/test_websocket_channel.py`` — new ``reasoning_delta``
/ ``reasoning_end`` frames, empty-chunk safety, no-subscriber safety,
back-compat expansion.
- ``tests/agent/test_runner_reasoning.py`` — runner closes the segment
on streaming answer start and after one-shot reasoning.
- WebUI ``useNanobotStream`` + ``message-bubble`` cover the new
protocol and the shimmer styling.
## Docs
``docs/configuration.md`` and ``docs/websocket.md`` document the new
events and the plugin contract.
Co-authored-by: Cursor <cursoragent@cursor.com>
