feat(thinking): improve config validation and codex support

- Add shouldShowWarnings() helper for cleaner warning control
- Improve applyThinkingSuffix() regex for accurate suffix detection
- Fix provider_overrides validation for nested tier structure
- Add thinking section to YAML config export with documentation
- Update UI to clarify codex uses reasoning effort levels
- Remove unused setManualOverride hook

src/cliproxy/config-generator.ts

@@ -25,6 +25,14 @@ import { supportsThinking } from './model-catalog';
 import { ThinkingConfig } from '../config/unified-config-types';
 import { validateThinking } from './thinking-validator';
 
+/**
+ * Check if warnings should be shown based on thinking config.
+ * Defaults to true if show_warnings is not explicitly false.
+ */
+function shouldShowWarnings(thinkingConfig: ThinkingConfig): boolean {
+  return thinkingConfig.show_warnings !== false;
+}
+
 /** Settings file structure for user overrides */
 interface ProviderSettings {
   env: NodeJS.ProcessEnv;
@@ -54,14 +62,11 @@ export function detectTierFromModel(modelName: string): ModelTier {
  * @param model - Base model name
  * @param thinkingValue - Level name (e.g., 'high') or numeric budget
  * @returns Model name with thinking suffix, e.g., "gemini-3-pro-preview(high)"
- *
- * @note Paren matching only handles one level. Nested parens like "model(foo)(8192)"
- *       will be treated as already having suffix and returned unchanged.
  */
 export function applyThinkingSuffix(model: string, thinkingValue: string | number): string {
-  // Don't apply if already has suffix
-  // NOTE: This only detects ANY paren pair, not proper nesting (e.g., "model(foo)(8192)" passes through)
-  if (model.includes('(') && model.includes(')')) {
+  // Don't apply if model already ends with a parenthesized suffix (e.g., "model(high)" or "model(8192)")
+  // Matches: ends with "(...)" where content is non-empty
+  if (/\([^)]+\)$/.test(model)) {
     return model;
   }
   return `${model}(${thinkingValue})`;
@@ -111,7 +116,7 @@ export function applyThinkingConfig(
   const baseModel = result.ANTHROPIC_MODEL || '';
   if (!supportsThinking(provider, baseModel)) {
     // U2: Warn user if they explicitly provided --thinking but model doesn't support it
-    if (thinkingOverride !== undefined && thinkingConfig.show_warnings !== false) {
+    if (thinkingOverride !== undefined && shouldShowWarnings(thinkingConfig)) {
       console.warn(
         warn(
           `Model ${baseModel || 'unknown'} (provider: ${provider}) does not support thinking budget. --thinking flag ignored.`
@@ -140,7 +145,7 @@ export function applyThinkingConfig(
 
   // Validate thinking value against model capabilities
   const validation = validateThinking(provider, baseModel, thinkingValue);
-  if (validation.warning && thinkingConfig.show_warnings !== false) {
+  if (validation.warning && shouldShowWarnings(thinkingConfig)) {
     console.warn(warn(validation.warning));
   }
   thinkingValue = validation.value;

src/config/unified-config-loader.ts

@@ -470,6 +470,25 @@ function generateYamlWithComments(config: UnifiedConfig): string {
     lines.push('');
   }
 
+  // Thinking section (extended thinking/reasoning configuration)
+  if (config.thinking) {
+    lines.push('# ----------------------------------------------------------------------------');
+    lines.push('# Thinking: Extended thinking/reasoning budget configuration');
+    lines.push('# Controls reasoning depth for supported providers (agy, gemini, codex).');
+    lines.push('#');
+    lines.push('# Modes: auto (use tier_defaults), off (disable), manual (--thinking flag only)');
+    lines.push('# Levels: minimal (512), low (1K), medium (8K), high (24K), xhigh (32K), auto');
+    lines.push('# Override: Set global override value (number or level name)');
+    lines.push('# Provider overrides: Per-provider tier defaults');
+    lines.push('# ----------------------------------------------------------------------------');
+    lines.push(
+      yaml
+        .dump({ thinking: config.thinking }, { indent: 2, lineWidth: -1, quotingType: '"' })
+        .trim()
+    );
+    lines.push('');
+  }
+
   // Dashboard auth section (only if configured)
   if (config.dashboard_auth?.enabled) {
     lines.push('# ----------------------------------------------------------------------------');

src/web-server/routes/misc-routes.ts

@@ -341,7 +341,7 @@ router.put('/thinking', (req: Request, res: Response): void => {
       }
     }
 
-    // C4: Validate provider_overrides if provided
+    // C4: Validate provider_overrides if provided (nested structure: Record<string, Partial<ThinkingTierDefaults>>)
     if (updates.provider_overrides !== undefined) {
       if (
         typeof updates.provider_overrides !== 'object' ||
@@ -352,19 +352,35 @@ router.put('/thinking', (req: Request, res: Response): void => {
         return;
       }
       const validLevels = [...VALID_THINKING_LEVELS] as string[];
-      for (const [provider, level] of Object.entries(updates.provider_overrides)) {
+      const validTiers = ['opus', 'sonnet', 'haiku'];
+      for (const [provider, tierOverrides] of Object.entries(updates.provider_overrides)) {
         if (typeof provider !== 'string' || provider.trim() === '') {
           res
             .status(400)
             .json({ error: 'Invalid provider_overrides: keys must be non-empty strings' });
           return;
         }
-        if (typeof level !== 'string' || !validLevels.includes(level)) {
+        // tierOverrides should be Partial<ThinkingTierDefaults>
+        if (typeof tierOverrides !== 'object' || tierOverrides === null) {
           res.status(400).json({
-            error: `Invalid level for provider ${provider}: must be one of ${validLevels.join(', ')}`,
+            error: `Invalid provider_overrides for ${provider}: must be an object with tier→level mapping`,
           });
           return;
         }
+        for (const [tier, level] of Object.entries(tierOverrides)) {
+          if (!validTiers.includes(tier)) {
+            res.status(400).json({
+              error: `Invalid tier '${tier}' in provider_overrides.${provider}: must be one of ${validTiers.join(', ')}`,
+            });
+            return;
+          }
+          if (typeof level !== 'string' || !validLevels.includes(level)) {
+            res.status(400).json({
+              error: `Invalid level for provider_overrides.${provider}.${tier}: must be one of ${validLevels.join(', ')}`,
+            });
+            return;
+          }
+        }
       }
     }
 

ui/src/pages/settings/hooks/use-thinking-config.ts

@@ -141,13 +141,6 @@ export function useThinkingConfig() {
     [saveConfig]
   );
 
-  const setManualOverride = useCallback(
-    (value: string | number | undefined) => {
-      saveConfig({ mode: 'manual', override: value });
-    },
-    [saveConfig]
-  );
-
   return {
     config: config || DEFAULT_THINKING_CONFIG,
     loading,
@@ -159,6 +152,5 @@ export function useThinkingConfig() {
     setMode,
     setTierDefault,
     setShowWarnings,
-    setManualOverride,
   };
 }

ui/src/pages/settings/sections/thinking/index.tsx

@@ -110,11 +110,14 @@ export default function ThinkingSection() {
             <Info className="w-4 h-4 text-blue-600 dark:text-blue-400 shrink-0 mt-0.5" />
             <div className="text-sm text-blue-700 dark:text-blue-300">
               <p className="font-medium">Supported Providers</p>
-              <p className="mt-1 text-blue-600 dark:text-blue-400">
-                Thinking budget works with: <strong>agy</strong> (Antigravity),{' '}
-                <strong>gemini</strong> (with thinking models). Other providers may ignore this
-                setting.
-              </p>
+              <ul className="mt-1 space-y-0.5 text-blue-600 dark:text-blue-400">
+                <li>
+                  Thinking budget: <strong>agy</strong>, <strong>gemini</strong> (token-based)
+                </li>
+                <li>
+                  Reasoning effort: <strong>codex</strong> (level-based: medium/high/xhigh)
+                </li>
+              </ul>
             </div>
           </div>