gate-fix #5480: suppress 'unknown' server version (case-insensitive) to prevent false banner

Codex gate: _normalizeWebUIVersion suppressed empty/__WEBUI_VERSION__/'not detected'
but NOT 'unknown' — api/updates.py emits WEBUI_VERSION='unknown' on git-describe
failure (Docker/CI images), so a real client version would falsely fire the
stale-client banner against server='unknown'. Suppress 'unknown' (+ case-insensitive
for all sentinels). + regression test asserting unknown/UNKNOWN/Unknown don't fire.

static/panels.js

@@ -2302,7 +2302,14 @@ async function hardRefreshWebUIClient(){
 function _normalizeWebUIVersion(value){
   if(!value) return '';
   const s=String(value).trim();
-  if(!s||s==='__WEBUI_VERSION__'||s==='not detected') return '';
+  if(!s) return '';
+  // Suppress placeholder / non-version sentinels (case-insensitive) so a real
+  // client version never "mismatches" against a server that couldn't detect its
+  // own version. api/updates.py can emit 'unknown' (git describe failure in a
+  // Docker/CI image); comparing a real version against 'unknown' would FALSELY
+  // fire the stale-client banner. (Codex #5480 gate)
+  const lower=s.toLowerCase();
+  if(lower==='__webui_version__'||lower==='not detected'||lower==='unknown') return '';
   return s;
 }
 

tests/test_5428_stale_client_recovery.py

@@ -177,6 +177,22 @@ def test_node_missing_server_version_no_banner():
     assert result["display"] != "flex", f"Banner wrongly shown for missing server version: {result}"
 
 
+def test_node_unknown_server_version_no_banner():
+    """A server that reports webui_version='unknown' (git-describe failure in a
+    Docker/CI image, api/updates.py) must NOT falsely fire the stale-client
+    banner against a real client version. (Codex #5480 gate)"""
+    helpers = _extract_skew_helpers(PANELS_JS.read_text(encoding="utf-8"))
+    for server_val in ("unknown", "UNKNOWN", "Unknown"):
+        result = _run_harness(
+            _make_stub("v1"),
+            helpers,
+            f'checkWebUIVersionSkew({{ webui_version: "{server_val}" }});',
+        )
+        assert result["display"] != "flex", (
+            f"Banner wrongly shown for server version {server_val!r}: {result}"
+        )
+
+
 def test_node_placeholder_client_version_no_banner():
     """Unresolved __WEBUI_VERSION__ literal as bundle stamp keeps banner hidden."""
     helpers = _extract_skew_helpers(PANELS_JS.read_text(encoding="utf-8"))