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_auth_regressions.py

@@ -233,9 +233,10 @@ def test_research_status_rejects_wrong_owner():
     rh.get_status.return_value = {"status": "running", "progress": {}}
     router = setup_research_routes(rh)
     target = next(r.endpoint for r in router.routes if getattr(r, "path", "") == "/api/research/status/{session_id}")
-    with pytest.raises(HTTPException) as exc:
-        asyncio.run(target(session_id="x", request=_fake_request(user="bob")))
-    assert exc.value.status_code == 404
+    # Another owner's research is indistinguishable from no research at all.
+    out = asyncio.run(target(session_id="x", request=_fake_request(user="bob")))
+    assert out == {"status": "none"}
+    rh.get_status.assert_not_called()
 
 
 def test_research_cancel_rejects_anonymous():