feat(security): apply audited PR #6738 remediations and test hardening

- Enforce vision probe SSRF safe local host validation, SafeProbeBackend TOCTOU elimination, and session owner authorization
- Authorize session titling endpoints against registered owner configuration
- Sanitize sensitive metadata logging from agent loop debug logs
- Add async non-blocking execution for spec router tools and thinking decisions
- Harden email cache invalidation fencing and thread-safe mutation
- Add regression test suites for legacy browser authority, spec contracts, spec router request scoping, and task MCP delivery

tests/test_task_shell_tools.py

@@ -107,6 +107,7 @@ async def test_scheduled_task_honors_global_disabled_tools(monkeypatch):
             return {"web_fetch"}
 
     monkeypatch.setattr("src.tool_index.get_tool_index", lambda: _FakeIndex())
+    monkeypatch.setattr("src.endpoint_resolver.resolve_owner_registered_endpoint", lambda *a, **k: object())
 
     captured = {}