diff --git a/static/ui.js b/static/ui.js
index a71b9bf7..37c49249 100644
--- a/static/ui.js
+++ b/static/ui.js
@@ -3214,6 +3214,16 @@ function _applyModelToDropdown(modelId, sel, preferredProviderId, opts){
   const resolved=_findModelInDropdown(modelId,sel,preferredProviderId);
   if(resolved){
     sel.value=resolved;
+    const preferredProvider=String(preferredProviderId||'').trim().toLowerCase();
+    if(preferredProvider&&sel.options){
+      // Assigning select.value picks the first duplicate value. Restore the
+      // provider-specific option that the caller matched (#6131).
+      const preferredOption=Array.from(sel.options).find(o=>
+        String(o.value||'')===String(resolved)
+        && String(_getOptionProviderId(o)||'').trim().toLowerCase()===preferredProvider
+      );
+      if(preferredOption) preferredOption.selected=true;
+    }
     if(isRichPickerSelect){
       const resolvedState=typeof _modelStateForSelect==='function'
         ? _modelStateForSelect(sel, resolved)
diff --git a/tests/test_issue6131_provider_aware_model_selection.py b/tests/test_issue6131_provider_aware_model_selection.py
new file mode 100644
index 00000000..74e982ca
--- /dev/null
+++ b/tests/test_issue6131_provider_aware_model_selection.py
@@ -0,0 +1,251 @@
+"""Regression coverage for provider-aware duplicate model selection (#6131)."""
+
+import json
+import shutil
+import subprocess
+from pathlib import Path
+
+import pytest
+
+
+ROOT = Path(__file__).resolve().parents[1]
+UI_JS = ROOT / "static" / "ui.js"
+NODE = shutil.which("node")
+
+
+_DRIVER = r"""
+const fs = require('fs');
+const uiSrc = fs.readFileSync(process.argv[1], 'utf8');
+const preferredProvider = process.argv[2] || '';
+
+function isIdentifierChar(ch) {
+  return /[A-Za-z0-9_$]/.test(ch || '');
+}
+
+function previousSignificantToken(source, index) {
+  let i = index - 1;
+  while (i >= 0 && /\s/.test(source[i])) i -= 1;
+  if (i < 0) return '';
+  if (!isIdentifierChar(source[i])) return source[i];
+  const end = i + 1;
+  while (i >= 0 && isIdentifierChar(source[i])) i -= 1;
+  return source.slice(i + 1, end);
+}
+
+function canStartRegexLiteral(source, index) {
+  const token = previousSignificantToken(source, index);
+  if (!token) return true;
+  if ('({[=,:;!&|?+-*~^<>'.includes(token)) return true;
+  return [
+    'return',
+    'throw',
+    'case',
+    'delete',
+    'typeof',
+    'void',
+    'new',
+    'in',
+    'of',
+    'yield',
+    'await',
+  ].includes(token);
+}
+
+function skipQuotedLiteral(source, index, quote) {
+  for (let i = index + 1; i < source.length; i += 1) {
+    if (source[i] === '\\') {
+      i += 1;
+      continue;
+    }
+    if (source[i] === quote) return i;
+  }
+  throw new Error('unterminated string literal');
+}
+
+function skipTemplateLiteral(source, index) {
+  for (let i = index + 1; i < source.length; i += 1) {
+    if (source[i] === '\\') {
+      i += 1;
+      continue;
+    }
+    if (source[i] === '`') return i;
+  }
+  throw new Error('unterminated template literal');
+}
+
+function skipLineComment(source, index) {
+  const end = source.indexOf('\n', index + 2);
+  return end < 0 ? source.length - 1 : end;
+}
+
+function skipBlockComment(source, index) {
+  const end = source.indexOf('*/', index + 2);
+  if (end < 0) throw new Error('unterminated block comment');
+  return end + 1;
+}
+
+function skipRegexLiteral(source, index) {
+  let inClass = false;
+  for (let i = index + 1; i < source.length; i += 1) {
+    if (source[i] === '\\') {
+      i += 1;
+      continue;
+    }
+    if (source[i] === '[') inClass = true;
+    else if (source[i] === ']') inClass = false;
+    else if (source[i] === '/' && !inClass) {
+      while (/[A-Za-z]/.test(source[i + 1] || '')) i += 1;
+      return i;
+    }
+  }
+  throw new Error('unterminated regex literal');
+}
+
+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 depth = 0;
+  for (let i = brace; i < source.length; i++) {
+    const ch = source[i];
+    const next = source[i + 1];
+    if (ch === '"' || ch === "'") i = skipQuotedLiteral(source, i, ch);
+    else if (ch === '`') i = skipTemplateLiteral(source, i);
+    else if (ch === '/' && next === '/') i = skipLineComment(source, i);
+    else if (ch === '/' && next === '*') i = skipBlockComment(source, i);
+    else if (ch === '/' && canStartRegexLiteral(source, i)) i = skipRegexLiteral(source, i);
+    else if (ch === '{') depth += 1;
+    else if (ch === '}') {
+      depth -= 1;
+      if (depth === 0) return source.slice(start, i + 1);
+    }
+  }
+  throw new Error('unterminated: ' + name);
+}
+
+function assertExtractorSkipsLexicalBraces() {
+  const trickySource = [
+    'function trickyExtractorTarget() {',
+    "  const stringValue = '}';",
+    '  const templateValue = `raw } ${1 + 1}`;',
+    '  const regexValue = /}/;',
+    '  // }',
+    '  /* { */',
+    '  return /}/.test(stringValue) ? templateValue : regexValue;',
+    '}',
+    'function afterTarget() { return 2; }',
+  ].join('\n');
+  const extracted = extractFunction(trickySource, 'trickyExtractorTarget');
+  if (!extracted.includes('return /}/.test') || extracted.includes('afterTarget')) {
+    throw new Error('extractFunction did not ignore lexical braces');
+  }
+}
+
+assertExtractorSkipsLexicalBraces();
+
+eval([
+  '_getOptionProviderId',
+  '_providerFromModelValue',
+  '_modelStateForSelect',
+  '_captureModelDropdownSelection',
+  '_findModelInDropdown',
+  '_applyModelToDropdown',
+].map(name => extractFunction(uiSrc, name)).join('\n'));
+
+globalThis._refreshOpenModelDropdown = () => {};
+globalThis.syncSettingsModelChip = () => {};
+
+const options = [
+  {
+    value: 'z-ai/glm-5.2',
+    textContent: 'GLM-5.2 via Z.AI',
+    dataset: {},
+    parentElement: {tagName: 'OPTGROUP', dataset: {provider: 'zai'}},
+  },
+  {
+    value: 'z-ai/glm-5.2',
+    textContent: 'GLM-5.2 via NVIDIA',
+    dataset: {},
+    parentElement: {tagName: 'OPTGROUP', dataset: {provider: 'nvidia'}},
+  },
+];
+
+let selectedIndex = 0;
+for (const option of options) {
+  Object.defineProperty(option, 'selected', {
+    get() { return options[selectedIndex] === option; },
+    set(value) { if (value) selectedIndex = options.indexOf(option); },
+  });
+}
+
+const select = {
+  id: 'settingsModel',
+  options,
+  get selectedIndex() { return selectedIndex; },
+  set selectedIndex(value) { selectedIndex = Number(value); },
+  get selectedOptions() {
+    return selectedIndex >= 0 ? [options[selectedIndex]] : [];
+  },
+  get value() {
+    return selectedIndex >= 0 ? options[selectedIndex].value : '';
+  },
+  set value(value) {
+    selectedIndex = options.findIndex(option => option.value === value);
+  },
+};
+
+const before = _modelStateForSelect(select, select.value);
+const applied = _applyModelToDropdown('z-ai/glm-5.2', select, preferredProvider);
+const after = _modelStateForSelect(select, select.value);
+const captured = _captureModelDropdownSelection(select);
+
+process.stdout.write(JSON.stringify({
+  before,
+  applied,
+  after,
+  captured,
+  selectedIndex,
+  selectedProvider: _getOptionProviderId(select.selectedOptions[0]),
+  optionProviders: options.map(option => _getOptionProviderId(option)),
+}));
+"""
+
+
+def _run_driver(preferred_provider: str) -> dict:
+    proc = subprocess.run(
+        [NODE, "-e", _DRIVER, str(UI_JS), preferred_provider],
+        capture_output=True,
+        text=True,
+        timeout=30,
+    )
+
+    assert proc.returncode == 0, proc.stderr
+    return json.loads(proc.stdout)
+
+
+@pytest.mark.skipif(NODE is None, reason="node not on PATH")
+def test_apply_model_dropdown_preserves_preferred_provider_for_duplicate_value():
+    result = _run_driver("nvidia")
+
+    assert result["before"]["model_provider"] == "zai"
+    assert result["applied"] == "z-ai/glm-5.2"
+    assert result["selectedIndex"] == 1
+    assert result["selectedProvider"] == "nvidia"
+    assert result["after"] == {
+        "model": "z-ai/glm-5.2",
+        "model_provider": "nvidia",
+    }
+    assert result["captured"] == result["after"]
+
+
+@pytest.mark.skipif(NODE is None, reason="node not on PATH")
+def test_apply_model_dropdown_does_not_fabricate_missing_provider_option():
+    result = _run_driver("anthropic")
+
+    assert result["applied"] == "z-ai/glm-5.2"
+    assert result["selectedIndex"] == 0
+    assert result["selectedProvider"] == "zai"
+    assert result["after"]["model_provider"] == "zai"
+    assert result["captured"] == result["after"]
+    assert result["optionProviders"] == ["zai", "nvidia"]