refactor(memory): drop on_session_reset — commit-only is enough

OV transparently handles message history across /new and /compress: old
messages stay in the same session and extraction is idempotent, so there's
no need to rebind providers to a new session_id. The only thing the
session boundary actually needs is to trigger extraction.

- MemoryProvider / MemoryManager: remove on_session_reset hook
- OpenViking: remove on_session_reset override (nothing to do)
- AIAgent: replace rotate_memory_session with commit_memory_session
  (just calls on_session_end, no rebind)
- cli.py / run_agent.py: single commit_memory_session call at the
  session boundary before session_id rotates
- tests: replace on_session_reset coverage with routing tests for
  MemoryManager.on_session_end

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

run_agent.py

@@ -3040,15 +3040,15 @@ class AIAgent:
             except Exception:
                 pass
     
-    def rotate_memory_session(self, new_session_id: str, messages: list = None) -> None:
-        """Commit the current memory session, then rebind providers to
-        new_session_id. Keeps HTTP clients/state alive across the transition.
-        Called when session_id rotates (e.g. /new, context compression)."""
+    def commit_memory_session(self, messages: list = None) -> None:
+        """Trigger end-of-session extraction without tearing providers down.
+        Called when session_id rotates (e.g. /new, context compression);
+        providers keep their state and continue running under the old
+        session_id — they just flush pending extraction now."""
         if not self._memory_manager:
             return
         try:
             self._memory_manager.on_session_end(messages or [])
-            self._memory_manager.on_session_reset(new_session_id)
         except Exception:
             pass
 
@@ -6838,11 +6838,11 @@ class AIAgent:
             try:
                 # Propagate title to the new session with auto-numbering
                 old_title = self._session_db.get_session_title(self.session_id)
+                # Trigger memory extraction on the old session before it rotates.
+                self.commit_memory_session(messages)
                 self._session_db.end_session(self.session_id, "compression")
                 old_session_id = self.session_id
                 self.session_id = f"{datetime.now().strftime('%Y%m%d_%H%M%S')}_{uuid.uuid4().hex[:6]}"
-                # Commit the old memory session and rebind providers to the new one.
-                self.rotate_memory_session(self.session_id, messages)
                 # Update session_log_file to point to the new session's JSON file
                 self.session_log_file = self.logs_dir / f"session_{self.session_id}.json"
                 self._session_db.create_session(