fix(models): prevent bare-id picker revert when provider hint is empty (#6195) (#6199)

Prevent bare-id model picker revert when the provider hint is empty: an ambiguous bare id that collides across provider groups no longer snaps to the default group on re-render. Adds a revert-sensitive regression test and fixes three cross-file test-isolation leaks found while gating. Thanks @webtecnica.

Co-authored-by: webtecnica <webtecnica@users.noreply.github.com>

tests/test_issue6195_bare_id_ambiguous_no_revert.py

@@ -0,0 +1,109 @@
+"""Regression for #6195 / #6199: a bare model id that collides with the profile
+default across multiple provider groups must NOT silently snap to the default
+group's option when no provider hint is available.
+
+`_findModelInDropdown('glm-5.2', sel, '')` previously returned the FIRST
+normalized match (`z-ai/glm-5.2`, the default group), so a deliberate non-default
+pick reverted to the default provider on re-render when the provider hint was
+momentarily unavailable. The Stage-2 guard now returns null in that ambiguous
+case so the caller injects a provider-scoped option instead of asserting the
+wrong provider.
+
+Invariants this locks in (proven against origin/master vs the fix):
+  - ambiguous bare id + EMPTY hint  -> null   (was: default-group snap)  [FIXED]
+  - ambiguous bare id + correct hint -> the hinted provider option        [unchanged]
+  - uniquely-named bare id           -> its single match                  [unchanged]
+  - bare id that IS an exact option value -> returned at Stage 0          [unchanged]
+"""
+
+from __future__ import annotations
+
+import json
+import shutil
+import subprocess
+from pathlib import Path
+
+import pytest
+
+REPO_ROOT = Path(__file__).parent.parent.resolve()
+UI_JS = REPO_ROOT / "static" / "ui.js"
+NODE = shutil.which("node")
+
+pytestmark = pytest.mark.skipif(NODE is None, reason="node not on PATH")
+
+_DRIVER = r"""
+const fs = require('fs');
+const uiSrc = fs.readFileSync(process.argv[1], 'utf8');
+
+function extractFunction(source, name){
+  const marker='function '+name+'(';
+  const start=source.indexOf(marker);
+  if(start<0) throw new Error('not found: '+name);
+  const brace=source.indexOf('{', source.indexOf(')', start));
+  let d=0;
+  for(let i=brace;i<source.length;i++){
+    if(source[i]==='{') d++;
+    else if(source[i]==='}'){ d--; if(d===0) return source.slice(start,i+1); }
+  }
+  throw new Error('unterminated: '+name);
+}
+
+eval([
+  '_getOptionProviderId',
+  '_providerFromModelValue',
+  '_findModelInDropdown',
+].map(name => extractFunction(uiSrc, name)).join('\n'));
+
+function makeOpt(value, provider){
+  return { value, textContent:value, dataset:{}, parentElement:{tagName:'OPTGROUP', dataset:{provider}} };
+}
+function makeSelect(options){
+  let idx = 0;
+  return {
+    id:'modelSelect', options,
+    querySelectorAll(){ return []; },
+    get selectedOptions(){ return idx>=0?[options[idx]]:[]; },
+    get value(){ return idx>=0?options[idx].value:''; },
+    set value(v){ idx = options.findIndex(o=>o.value===v); },
+  };
+}
+
+const AMB = () => [ makeOpt('z-ai/glm-5.2','z-ai'), makeOpt('@custom:tokenrouter:z-ai/glm-5.2','custom:tokenrouter') ];
+
+const out = {
+  // #6195 repro: ambiguous bare id, no hint -> must be null (not a default-group snap)
+  ambiguousEmptyHint: _findModelInDropdown('glm-5.2', makeSelect(AMB()), ''),
+  // with the correct hint -> resolves to the hinted provider (unchanged)
+  ambiguousWithHint: _findModelInDropdown('glm-5.2', makeSelect(AMB()), 'custom:tokenrouter'),
+  // uniquely-named bare id still matches (unchanged)
+  uniqueBare: _findModelInDropdown('glm-5.2-free', makeSelect([makeOpt('z-ai/glm-5.2-free','z-ai')]), ''),
+  // bare id that IS an exact option value -> returned at Stage 0 even when ambiguous (unchanged)
+  bareExactAmbiguous: _findModelInDropdown('glm-5.2', makeSelect([makeOpt('glm-5.2','z-ai'), makeOpt('@custom:tokenrouter:glm-5.2','custom:tokenrouter')]), ''),
+};
+process.stdout.write(JSON.stringify(out));
+"""
+
+
+def _run():
+    assert NODE is not None
+    result = subprocess.run([NODE, "-e", _DRIVER, str(UI_JS)],
+                            capture_output=True, text=True, timeout=30)
+    assert result.returncode == 0, result.stderr
+    return json.loads(result.stdout)
+
+
+def test_ambiguous_bare_id_no_hint_does_not_snap_to_default():
+    # THE fix: no wrong-provider revert. null => caller injects a scoped option.
+    assert _run()["ambiguousEmptyHint"] is None
+
+
+def test_ambiguous_bare_id_with_hint_resolves_to_hinted_provider():
+    assert _run()["ambiguousWithHint"] == "@custom:tokenrouter:z-ai/glm-5.2"
+
+
+def test_unique_bare_id_still_matches():
+    assert _run()["uniqueBare"] == "z-ai/glm-5.2-free"
+
+
+def test_bare_id_that_is_exact_option_value_returns_at_stage0():
+    assert _run()["bareExactAmbiguous"] == "glm-5.2"