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>

api/models.py

@@ -44,6 +44,10 @@ class Session:
                  project_id: str=None, profile=None,
                  input_tokens: int=0, output_tokens: int=0, estimated_cost=None,
                  personality=None,
+                 active_stream_id: str=None,
+                 pending_user_message: str=None,
+                 pending_attachments=None,
+                 pending_started_at=None,
                  **kwargs):
         self.session_id = session_id or uuid.uuid4().hex[:12]
         self.title = title
@@ -61,6 +65,10 @@ class Session:
         self.output_tokens = output_tokens or 0
         self.estimated_cost = estimated_cost
         self.personality = personality
+        self.active_stream_id = active_stream_id
+        self.pending_user_message = pending_user_message
+        self.pending_attachments = pending_attachments or []
+        self.pending_started_at = pending_started_at
 
     @property
     def path(self):