fix: live reasoning, tool progress, in-flight session recovery (#367)

* fix: preserve live session output across chat switches

(cherry picked from commit 401e3b643d25e8dad8c06883b478b3c3073f07a5)

* fix: preserve todo state after session reload

(cherry picked from commit 7ee093ba19978af23b79148df2f2347e2f1e5bde)

* fix: preserve live assistant anchor across rerenders

* fix: stream live reasoning and tool progress

* fix: recover inflight session state after reload

* fix: add loadInflightState stub + CHANGELOG v0.50.21

- static/ui.js: add loadInflightState() function (currently returns null —
  the typeof guard in sessions.js means reload recovery works via the
  else-path attachLiveStream call; this stub satisfies the guard cleanly
  and documents the extension point for future localStorage-backed state)
- CHANGELOG.md: v0.50.21 entry; 960 tests (up from 949)

---------

Co-authored-by: Jordan SkyLF <jordan@skylinkfiber.net>
Co-authored-by: Nathan Esquenazi <nesquena@gmail.com>

CHANGELOG.md

@@ -10,6 +10,17 @@
 - **Workspace file downloads no longer crash for Unicode filenames** (`api/routes.py`): Clicking a PDF or other file with Chinese, Japanese, Arabic, or other non-ASCII characters in its name caused a `UnicodeEncodeError` because Python's HTTP server requires header values to be latin-1 encodable. A new `_content_disposition_value(disposition, filename)` helper centralises `Content-Disposition` generation: it strips CR/LF (injection guard), builds an ASCII fallback for the legacy `filename=` parameter (non-ASCII chars replaced with `_`), and preserves the full UTF-8 name in `filename*=UTF-8''...` per RFC 5987. Both `attachment` and `inline` responses use it.
   - 2 new integration tests in `tests/test_sprint29.py` covering Chinese filenames for both download and inline responses, verifying the header is latin-1 encodable and `filename*=UTF-8''` is present; 924 tests total (up from 922)
 
+## [v0.50.21] Live reasoning, tool progress, and in-flight session recovery (PR #367)
+
+- **Live reasoning cards during streaming** (`static/ui.js`, `static/messages.js`): The generic thinking spinner now upgrades to a live reasoning card when the backend streams reasoning text. `_thinkingMarkup(text)` and `updateThinking(text)` centralize the markup so the spinner and card share the same DOM slot. Works with models that emit reasoning via the agent's `reasoning_callback` or `tool_progress_callback`.
+- **`tool_complete` SSE events** (`api/streaming.py`, `static/messages.js`): Tool progress callback now accepts the current agent signature `on_tool(*cb_args, **cb_kwargs)` — handles both the old 3-arg `(name, preview, args)` form and the new 4-arg `(event_type, name, preview, args)` form. `tool.completed` events transition live tool cards from running to done cleanly.
+- **In-flight session state stable across switches** (`static/messages.js`, `static/sessions.js`): `attachLiveStream` refactored out of `send()` into a standalone function; partial assistant text mirrored into `INFLIGHT` state on every token; `data-live-assistant` DOM anchor preserved across `renderMessages()` calls so switching away and back doesn't lose or duplicate live output.
+- **Reload recovery** (`api/models.py`, `api/routes.py`, `api/streaming.py`, `static/sessions.js`): `active_stream_id`, `pending_user_message`, `pending_attachments`, and `pending_started_at` now persisted on the session object before streaming starts and cleared on completion (or exception). `/api/session` returns these fields. After a page reload or session switch, `loadSession()` detects `active_stream_id` and calls `attachLiveStream(..., {reconnecting:true})` to reattach to the live SSE stream.
+- **Session-scoped message queue** (`static/ui.js`, `static/messages.js`): Global `MSG_QUEUE` replaced with `SESSION_QUEUES` keyed by session ID. Queued follow-up messages are associated with the session they were typed in and only drained when that session becomes idle — no cross-session bleed.
+- **`newSession()` idle reset** (`static/sessions.js`): Sets `S.busy=false`, `S.activeStreamId=null`, clears the cancel button, resets composer status — ensures a fresh chat is immediately usable even if another session's stream is still running.
+- **Todos survive session reload** (`static/panels.js`): `loadTodos()` now reads from `S.session.messages` (raw, includes tool-role messages) rather than `S.messages` (filtered display), so todo state reconstructed from tool outputs survives reloads.
+  - 12 new regression tests in `tests/test_regressions.py`; 960 tests total (up from 949)
+
 ## [v0.50.20] Silent error fix, stale model cleanup, live model fetching (fixes #373, #374, #375)
 
 ### Fix: Chat no longer silently swallows agent failures (fixes #373)