refactor(memory): promote on_session_reset to base provider hook

Replace hasattr-forked OpenViking-specific paths with a proper base-class
hook. Collapse the two agent wrappers into a single rotate_memory_session
so callers don't orchestrate commit + rebind themselves.

- MemoryProvider: add on_session_reset(new_session_id) as a default no-op
- MemoryManager: on_session_reset fans out unconditionally (no hasattr,
  no builtin skip — base no-op covers it)
- OpenViking: rename reset_session -> on_session_reset; drop the explicit
  POST /api/v1/sessions (OV auto-creates on first message) and the two
  debug raise_for_status wrappers
- AIAgent: collapse commit_memory_session + reinitialize_memory_session
  into rotate_memory_session(new_sid, messages)
- cli.py / run_agent.py: replace hasattr blocks and the split calls with
  a single unconditional rotate_memory_session call; compression path
  now passes the real messages list instead of []
- tests: align with on_session_reset, assert reset does NOT POST /sessions

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

cli.py

@@ -4095,18 +4095,12 @@ class HermesCLI:
 
     def new_session(self, silent=False):
         """Start a fresh session with a new session ID and cleared agent state."""
-        if self.agent and self.conversation_history:
+        old_history = self.conversation_history
+        if self.agent and old_history:
             try:
-                self.agent.flush_memories(self.conversation_history)
+                self.agent.flush_memories(old_history)
             except (Exception, KeyboardInterrupt):
                 pass
-            # Commit external memory providers (e.g. OpenViking) BEFORE
-            # session_id changes so extraction runs on the correct session.
-            if hasattr(self.agent, "commit_memory_session"):
-                try:
-                    self.agent.commit_memory_session(self.conversation_history)
-                except Exception:
-                    pass
             self._notify_session_boundary("on_session_finalize")
         elif self.agent:
             # First session or empty history — still finalize the old session
@@ -4155,13 +4149,9 @@ class HermesCLI:
                     )
                 except Exception:
                     pass
-            # Reinitialize external memory providers with the new session_id
-            # so subsequent turns are tracked under the new session.
-            if hasattr(self.agent, "reinitialize_memory_session"):
-                try:
-                    self.agent.reinitialize_memory_session(self.session_id)
-                except Exception:
-                    pass
+            # Commit the old session and rebind memory providers to the
+            # new session_id so subsequent turns are tracked correctly.
+            self.agent.rotate_memory_session(self.session_id, old_history)
             self._notify_session_boundary("on_session_reset")
 
         if not silent: