feat(api): add /api/thinking endpoints for budget config

- GET /api/thinking returns current config

- PUT /api/thinking updates mode/override/tier_defaults

- validate override bounds and level names

Refs #307

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

@@ -11,7 +11,15 @@ import {
   loadOrCreateUnifiedConfig,
   saveUnifiedConfig,
   getGlobalEnvConfig,
+  getThinkingConfig,
 } from '../../config/unified-config-loader';
+import type { ThinkingConfig } from '../../config/unified-config-types';
+import {
+  THINKING_BUDGET_MIN,
+  THINKING_BUDGET_MAX,
+  VALID_THINKING_LEVELS,
+  THINKING_OFF_VALUES,
+} from '../../cliproxy';
 import { validateFilePath } from './route-helpers';
 
 const router = Router();
@@ -221,4 +229,99 @@ router.put('/global-env', (req: Request, res: Response): void => {
   }
 });
 
+// ==================== Thinking Configuration ====================
+
+/**
+ * GET /api/thinking - Get thinking budget configuration
+ * Returns the thinking section from config.yaml
+ */
+router.get('/thinking', (_req: Request, res: Response): void => {
+  try {
+    const config = getThinkingConfig();
+    res.json({ config });
+  } catch (error) {
+    res.status(500).json({ error: (error as Error).message });
+  }
+});
+
+/**
+ * PUT /api/thinking - Update thinking budget configuration
+ * Updates the thinking section in config.yaml
+ */
+router.put('/thinking', (req: Request, res: Response): void => {
+  try {
+    const updates = req.body as Partial<ThinkingConfig>;
+    const config = loadOrCreateUnifiedConfig();
+
+    // Validate mode if provided
+    if (updates.mode !== undefined) {
+      const validModes = ['auto', 'off', 'manual'];
+      if (!validModes.includes(updates.mode)) {
+        res.status(400).json({ error: `Invalid mode: must be one of ${validModes.join(', ')}` });
+        return;
+      }
+    }
+
+    // Validate override if provided (budget or level)
+    if (updates.override !== undefined) {
+      if (typeof updates.override === 'number') {
+        if (
+          !Number.isFinite(updates.override) ||
+          updates.override < THINKING_BUDGET_MIN ||
+          updates.override > THINKING_BUDGET_MAX
+        ) {
+          res.status(400).json({
+            error: `Invalid override: must be between ${THINKING_BUDGET_MIN} and ${THINKING_BUDGET_MAX}`,
+          });
+          return;
+        }
+      } else if (typeof updates.override === 'string') {
+        const normalizedValue = updates.override.toLowerCase().trim();
+        const validValues = [...VALID_THINKING_LEVELS, ...THINKING_OFF_VALUES] as readonly string[];
+        if (!validValues.includes(normalizedValue)) {
+          res.status(400).json({
+            error: `Invalid override: must be a level name (${VALID_THINKING_LEVELS.join(', ')}) or a number`,
+          });
+          return;
+        }
+      }
+    }
+
+    // Validate tier_defaults if provided
+    if (updates.tier_defaults !== undefined) {
+      const validLevels = [...VALID_THINKING_LEVELS] as string[];
+      for (const [tier, level] of Object.entries(updates.tier_defaults)) {
+        if (!['opus', 'sonnet', 'haiku'].includes(tier)) {
+          res.status(400).json({ error: `Invalid tier: ${tier}` });
+          return;
+        }
+        if (!validLevels.includes(level)) {
+          res.status(400).json({
+            error: `Invalid level for ${tier}: must be one of ${validLevels.join(', ')}`,
+          });
+          return;
+        }
+      }
+    }
+
+    // Update thinking section
+    config.thinking = {
+      mode: updates.mode ?? config.thinking?.mode ?? 'auto',
+      override: updates.override ?? config.thinking?.override,
+      tier_defaults: {
+        opus: updates.tier_defaults?.opus ?? config.thinking?.tier_defaults?.opus ?? 'high',
+        sonnet: updates.tier_defaults?.sonnet ?? config.thinking?.tier_defaults?.sonnet ?? 'medium',
+        haiku: updates.tier_defaults?.haiku ?? config.thinking?.tier_defaults?.haiku ?? 'low',
+      },
+      provider_overrides: updates.provider_overrides ?? config.thinking?.provider_overrides,
+      show_warnings: updates.show_warnings ?? config.thinking?.show_warnings ?? true,
+    };
+
+    saveUnifiedConfig(config);
+    res.json({ success: true, config: config.thinking });
+  } catch (error) {
+    res.status(500).json({ error: (error as Error).message });
+  }
+});
+
 export default router;