fix(openviking): commit session on /new and context compression

The OpenViking memory provider extracts memories when its session is
committed (POST /api/v1/sessions/{id}/commit).  Before this fix, the
CLI had two code paths that changed the active session_id without ever
committing the outgoing OpenViking session:

1. /new (new_session() in cli.py) — called flush_memories() to write
   MEMORY.md, then immediately discarded the old session_id.  The
   accumulated OpenViking session was never committed, so all context
   from that session was lost before extraction could run.

2. /compress and auto-compress (_compress_context() in run_agent.py) —
   split the SQLite session (new session_id) but left the OpenViking
   provider pointing at the old session_id with no commit, meaning all
   messages synced to OpenViking were silently orphaned.

The gateway already handles session commit on /new and /reset via
shutdown_memory_provider() on the cached agent; the CLI path did not.

Fix: introduce a lightweight session-transition lifecycle alongside
the existing full shutdown path:

- OpenVikingMemoryProvider.reset_session(new_session_id): waits for
  in-flight background threads, resets per-session counters, and
  creates the new OV session via POST /api/v1/sessions — without
  tearing down the HTTP client (avoids connection overhead on /new).

- MemoryManager.restart_session(new_session_id): calls reset_session()
  on providers that implement it; falls back to initialize() for
  providers that do not.  Skips the builtin provider (no per-session
  state).

- AIAgent.commit_memory_session(messages): wraps
  memory_manager.on_session_end() without shutdown — commits OV session
  for extraction but leaves the provider alive for the next session.

- AIAgent.reinitialize_memory_session(new_session_id): wraps
  memory_manager.restart_session() — transitions all external providers
  to the new session after session_id has been assigned.

Call sites:
- cli.py new_session(): commit BEFORE session_id changes, reinitialize
  AFTER — ensuring OV extraction runs on the correct session and the
  new session is immediately ready for the next turn.
- run_agent._compress_context(): same pattern, inside the
  if self._session_db: block where the session_id split happens.

/compress and auto-compress are functionally identical at this layer:
both call _compress_context(), so both are fixed by the same change.

Tests added to tests/agent/test_memory_provider.py:
- TestMemoryManagerRestartSession: reset_session() routing, builtin
  skip, initialize() fallback, failure tolerance, empty-manager noop.
- TestOpenVikingResetSession: session_id update, per-session state
  clear, POST /api/v1/sessions call, API failure tolerance, no-client
  noop.

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

run_agent.py

@@ -3040,6 +3040,34 @@ class AIAgent:
             except Exception:
                 pass
     
+    def commit_memory_session(self, messages: list = None) -> None:
+        """Commit external memory providers for the current session.
+
+        Calls on_session_end() WITHOUT shutting down providers — the session
+        data (e.g. OpenViking) is committed for extraction, but the HTTP
+        client and provider state remain alive for the next session.
+        Called before session_id changes (e.g. /new, context compression).
+        """
+        if self._memory_manager:
+            try:
+                self._memory_manager.on_session_end(messages or [])
+            except Exception:
+                pass
+
+    def reinitialize_memory_session(self, new_session_id: str) -> None:
+        """Transition memory providers to a new session after commit.
+
+        Calls restart_session() which uses reset_session() on providers that
+        support it (cheap: keeps HTTP client, resets per-session counters) or
+        falls back to initialize() for providers that don't.
+        Called after session_id has been assigned (e.g. /new, compression).
+        """
+        if self._memory_manager:
+            try:
+                self._memory_manager.restart_session(new_session_id)
+            except Exception:
+                pass
+
     def close(self) -> None:
         """Release all resources held by this agent instance.
 
@@ -6826,9 +6854,14 @@ class AIAgent:
             try:
                 # Propagate title to the new session with auto-numbering
                 old_title = self._session_db.get_session_title(self.session_id)
+                # Commit external memory (e.g. OpenViking) before session_id
+                # changes so extraction runs on the correct session.
+                self.commit_memory_session([])
                 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]}"
+                # Transition external memory providers to the new session_id.
+                self.reinitialize_memory_session(self.session_id)
                 # 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(