fix(lib): prevent set -u unbound variable error for final_cmd in kind detection and harden test fixtures

tests/test_tier3_integration.py

@@ -2,6 +2,7 @@ import os
 import subprocess
 import json
 import sqlite3
+import fcntl
 import pytest
 import shutil
 import yaml
@@ -117,19 +118,23 @@ def test_integration_stop_purge_combination(mam_sandbox, mock_herdr, mock_agents
     assert jsonl_file.exists()
     
     # Update mock herdr's state to match the running agent so the stop kill-chain works gracefully
-    with open(mock_herdr, 'r') as f:
-        state = json.load(f)
-    state["agents"][session_name] = {
-        "status": "running",
-        "agent": "claude",
-        "cwd": str(tmp_path),
-        "pid": 12345,
-        "pane_id": "w1:p1",
-        "command": "claude",
-        "buffer": "Anthropic Claude Ready"
-    }
-    with open(mock_herdr, 'w') as f:
-        json.dump(state, f, indent=2)
+    lock_path = str(mock_herdr) + ".lock"
+    with open(lock_path, 'a') as lock_f:
+        fcntl.flock(lock_f, fcntl.LOCK_EX)
+        with open(mock_herdr, 'r') as f:
+            state = json.load(f)
+        state["agents"][session_name] = {
+            "status": "running",
+            "agent": "claude",
+            "cwd": str(tmp_path),
+            "pid": 12345,
+            "pane_id": f"w1:p_{session_name}",
+            "command": "claude",
+            "buffer": "Anthropic Claude Ready"
+        }
+        with open(mock_herdr, 'w') as f:
+            json.dump(state, f, indent=2)
+        fcntl.flock(lock_f, fcntl.LOCK_UN)
 
     # 2. Calling stop_session without --yes fails for --purge-conversation
     stop_script = tmp_path / "skills" / "multi-agent-mux-stop" / "scripts" / "stop_session.sh"