fix(ui): #3429 round-2 — never fall back to authority or placeholder (Codex MUST-FIX)

Codex re-check: degenerate URIs still leaked — gpt://folder123 returned the
authority, gpt://folder123/${MODEL} returned the placeholder. Removed the _all[0]
authority fallback and guarded the literal-last-path fallback against placeholders;
a URI with no usable model segment now falls back to the raw id. Added regression
cases for gpt://folder123 and gpt://folder123/${MODEL}.

static/ui.js

@@ -2930,9 +2930,12 @@ function getModelLabel(modelId){
       if (!_lastUsable) _lastUsable = _seg;
       if (!_isVersionTail(_seg)) { _pick = _seg; break; }
     }
-    // Fallbacks: last non-placeholder path segment, else the literal last path
-    // segment, else the authority, else the raw id. Never an env-var placeholder.
-    _last = _pick || _lastUsable || _path[_path.length - 1] || _all[0] || modelId;
+    // Fallbacks: the chosen non-version segment, else the last non-placeholder
+    // path segment. NEVER the authority and NEVER a `${...}` placeholder — for
+    // a degenerate id (`gpt://folder123`, `gpt://folder123/${MODEL}`) fall all
+    // the way back to the raw id rather than leak the folder/host or env var.
+    const _lastPath = _path[_path.length - 1] || '';
+    _last = _pick || _lastUsable || (_lastPath && !_isPlaceholder(_lastPath) ? _lastPath : '') || modelId;
   } else {
     _last = modelId.includes('/') ? (modelId.slice(modelId.indexOf('/')+1) || modelId) : modelId;
   }

tests/test_issue3429_uri_scheme_model_label.py

@@ -88,6 +88,20 @@ def test_uri_label_edge_cases_never_return_authority_or_drop_digit_models():
         assert label != "folder123", "authority/folder leaked into label"
 
 
+def test_uri_degenerate_ids_fall_back_to_raw_not_authority_or_placeholder():
+    """#3429 follow-up 2 (Codex gate): a URI with no usable model segment must
+    fall back to the raw id — never the authority/folder, never a ${...} env-var."""
+    out = _labels([
+        "gpt://folder123",              # authority only, no path
+        "gpt://folder123/${MODEL}",     # path is only an env-var placeholder
+    ])
+    assert out["gpt://folder123"] == "gpt://folder123"
+    assert out["gpt://folder123/${MODEL}"] == "gpt://folder123/${MODEL}"
+    for label in out.values():
+        assert label != "folder123", "authority leaked into label"
+        assert label not in ("${MODEL}",), "env-var placeholder leaked into label"
+
+
 def test_uri_fix_does_not_regress_multi_slash_or_bare_ids():
     """#3360 multi-slash hierarchy + single-slash/bare ids stay correct."""
     out = _labels([