fix(reset,stop): warn before a reset purges, skip and prune stale registries, refuse a guessed purge

reset.sh without --yes says the conversations are deleted for good before it
asks; without a terminal the refusal says so too. A registry that cannot be
created is skipped, since nothing can be registered there, and the directories
the fence created are removed on exit when still empty. stop --purge-conversation
refuses a conversation the row does not record instead of deleting the folder's
newest one.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VCgu9Fa9iT7TbJUSzdq4Ff

.agents/skills/lib_py/agents/session_ids.py

@@ -154,6 +154,13 @@ def decide_stop(state: Dict[str, Any], name: str, agent: str, cwd: str,
                 "purge_uuid": "",
                 "note": f"{found} is also recorded by {others}; registry needs fixing",
             }
+        if purge and found and found != own:
+            return {
+                "captured": "",
+                "status": "purge-unrecorded",
+                "purge_uuid": "",
+                "note": f"{found} is this folder's newest conversation, not an id this row records",
+            }
         return {
             "captured": found,
             "status": "resolved" if found else "no-candidate",