Fix save doesn't store default agent.

Author: beacoder

python_agent_harness/entry/restore.py

@@ -79,8 +79,12 @@ def load_saved_session(path: str) -> SavedSession:
 
 
 def restore_agent(controller: Controller, agent: str | None, report: Report) -> None:
-    """Switch to the saved AGENT; fall back to the default agent (so no
-    stale tool exclusions linger) when it no longer exists."""
+    """Switch to the saved AGENT; keep the current agent when the session
+    was saved without one (pre-agent-era file), and fall back to the
+    default agent (so no stale tool exclusions linger) when the saved
+    name no longer exists.  A session saved on the default agent records
+    ``default`` explicitly (see SessionPersistence.metadata_block), so it
+    still switches back even when a custom agent is active now."""
     if not agent:
         return
     try:

python_agent_harness/io/persistence.py

@@ -170,10 +170,18 @@ def first_user_message(self) -> str | None:
     # -- saving ---------------------------------------------------------------
     def metadata_block(self) -> str:
         lines = [";; Local Variables:"]
+        # The agent is ALWAYS recorded: the built-in default is stored
+        # as "default" rather than omitted, so "saved on the default
+        # agent" stays distinguishable from a pre-agent-era file (no
+        # key at all) and /restore can switch a currently-active custom
+        # agent back to the default prompt.  switch_agent also stores
+        # None there on a default switch (see Session.switch_agent),
+        # which is normalized to the reserved name here.
+        agent = self.agent if self.agent else "default"
         pairs = [
             ("python-agent-harness--project-dir", self.project_dir),
             ("python-agent-harness--model", self.model),
-            ("python-agent-harness--agent", self.agent),
+            ("python-agent-harness--agent", agent),
         ]
         for name, value in pairs:
             if value is None:

tests/io/test_persistence.py

@@ -74,11 +74,18 @@ def test_agent_persisted_in_metadata(self):
         parsed = SessionPersistence.parse_metadata(text)
         self.assertEqual(parsed["python-agent-harness--agent"], "reviewer")
 
-    def test_agent_absent_when_none(self):
-        """No custom agent -> no agent line in the metadata block, so
-        old sessions and default-agent sessions parse identically."""
+    def test_default_agent_recorded_explicitly(self):
+        """A session saved on the built-in default agent records
+        ``default`` explicitly: without it, "saved on default" would be
+        indistinguishable from a pre-agent-era file (no key at all), and
+        /restore would keep whatever custom agent happens to be active
+        in the current session instead of switching back to default."""
         store = SessionPersistence(project_dir="/tmp/proj", model="m", agent=None)
-        self.assertNotIn("python-agent-harness--agent", store.metadata_block())
+        meta = store.metadata_block()
+        self.assertIn("python-agent-harness--agent: 'default'", meta)
+        text = "conversation...\n\n" + meta + "\n"
+        parsed = SessionPersistence.parse_metadata(text)
+        self.assertEqual(parsed["python-agent-harness--agent"], "default")
 
     def test_save_and_restore_flow(self):
         import os