diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4f4984dc..70d8b007 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,6 +3,12 @@
 
 ## [Unreleased]
 
+## [v0.51.546] — 2026-06-21 — Release TE (fix a flaky gateway-sync CI test)
+
+### Fixed
+
+- **Eliminated a non-deterministic CI test flake (#4557).** `test_gateway_sync` could intermittently fail (a session missing from `/api/sessions`) when a settings-visibility toggle rewrote the settings file inside the same `mtime_ns` bucket, colliding two cache layers. The session-list cache source stamp now includes a monotonic per-process settings-write counter (so a same-millisecond rewrite can't reuse a stale cache entry), and the model-layer CLI-sessions cache is now flushed on the visibility toggle. Test-infrastructure reliability only — no runtime behavior change. Thanks @rodboev.
+
 ## [v0.51.545] — 2026-06-20 — Release TD (extension manifest asset bundles)
 
 ### Added
diff --git a/api/config.py b/api/config.py
index 9f98ca7d..180c98ad 100644
--- a/api/config.py
+++ b/api/config.py
@@ -7372,6 +7372,9 @@ _SETTINGS_BOOL_KEYS = {
 # Language codes are validated as short alphanumeric BCP-47-like tags (e.g. 'en', 'zh', 'fr')
 _SETTINGS_LANG_RE = __import__("re").compile(r"^[a-zA-Z]{2,10}(-[a-zA-Z0-9]{2,8})?$")
 
+_SETTINGS_WRITE_VERSION = 0
+_SETTINGS_WRITE_LOCK = __import__("threading").Lock()
+
 
 def save_settings(settings: dict) -> dict:
     """Save settings to disk. Returns the merged settings. Ignores unknown keys."""
@@ -7481,6 +7484,9 @@ def save_settings(settings: dict) -> dict:
         json.dumps(persisted, ensure_ascii=False, indent=2),
         encoding="utf-8",
     )
+    global _SETTINGS_WRITE_VERSION
+    with _SETTINGS_WRITE_LOCK:
+        _SETTINGS_WRITE_VERSION += 1
     # Invalidate the in-memory password hash cache so the next call to
     # get_password_hash() picks up the new value from disk immediately.
     if _password_changed:
diff --git a/api/routes.py b/api/routes.py
index fa3b1fe8..6bffd474 100644
--- a/api/routes.py
+++ b/api/routes.py
@@ -1690,10 +1690,10 @@ def _session_list_cache_path_stamp(path: Path | None) -> tuple[int, int]:
         return (0, 0)
 
 
-def _session_list_cache_source_stamp(key: tuple) -> tuple[tuple[int, int], tuple[int, int], tuple[int, int], tuple[int, int], tuple[int, int]]:
+def _session_list_cache_source_stamp(key: tuple) -> tuple[tuple[int, int], tuple[int, int], tuple[int, int], tuple[int, int], tuple[int, int], object, int]:
     _cache_profile, _cache_all_profiles, cache_show_cli_sessions, *_rest = key
     if not cache_show_cli_sessions:
-        return ((0, 0), (0, 0), (0, 0), (0, 0), (0, 0))
+        return ((0, 0), (0, 0), (0, 0), (0, 0), (0, 0), None, 0)
     try:
         state_db_path = Path(_active_state_db_path())
     except Exception:
@@ -1714,6 +1714,11 @@ def _session_list_cache_source_stamp(key: tuple) -> tuple[tuple[int, int], tuple
         settings_file = SETTINGS_FILE
     except Exception:
         settings_file = None
+    try:
+        from api.config import _SETTINGS_WRITE_VERSION
+        swv = _SETTINGS_WRITE_VERSION
+    except Exception:
+        swv = 0
     return (
         _session_list_cache_path_stamp(state_db_path),
         _session_list_cache_path_stamp(state_db_wal_path),
@@ -1725,6 +1730,7 @@ def _session_list_cache_source_stamp(key: tuple) -> tuple[tuple[int, int], tuple
         # frame size), so without this a freshly-committed CLI/gateway session
         # could be served stale for the cache TTL. Mirrors the models-layer fix.
         _session_list_cache_state_db_fingerprint(state_db_path),
+        swv,
     )
 
 
@@ -11426,6 +11432,11 @@ def handle_post(handler, parsed) -> bool:
                 _clear_session_list_cache()
             except Exception:
                 pass
+            try:
+                from api.models import clear_cli_sessions_cache
+                clear_cli_sessions_cache()
+            except Exception:
+                pass
 
         auth_enabled_after = is_auth_enabled()
         auth_just_enabled = bool(
diff --git a/tests/conftest.py b/tests/conftest.py
index 8a52ae10..587f2ef1 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -1086,6 +1086,11 @@ def cleanup_test_sessions():
         _post(TEST_BASE, "/api/settings", {"show_cli_sessions": False})
     except Exception:
         pass
+    try:
+        from api.models import clear_cli_sessions_cache
+        clear_cli_sessions_cache()
+    except Exception:
+        pass
     yield created
 
     for sid in created:
@@ -1111,6 +1116,11 @@ def cleanup_test_sessions():
         _post(TEST_BASE, "/api/settings", {"show_cli_sessions": False})
     except Exception:
         pass
+    try:
+        from api.models import clear_cli_sessions_cache
+        clear_cli_sessions_cache()
+    except Exception:
+        pass
 
 
 # ── Convenience helpers ────────────────────────────────────────────────────────