fix(ui): add provider indicator, retry button, and optimistic locking

- U4: add blue info box showing supported providers

- W1: add inline retry button in error alert

- W4: track lastModified, handle 409 conflict with auto-refresh

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

@@ -1,9 +1,10 @@
 /**
  * Thinking Config Hook
  * Manages thinking budget configuration with direct API calls
+ * Includes W4 optimistic locking via lastModified timestamps
  */
 
-import { useCallback, useState } from 'react';
+import { useCallback, useState, useRef } from 'react';
 import type { ThinkingConfig, ThinkingMode } from '../types';
 
 const DEFAULT_THINKING_CONFIG: ThinkingConfig = {
@@ -24,6 +25,8 @@ export function useThinkingConfig() {
   const [saving, setSaving] = useState(false);
   const [error, setError] = useState<string | null>(null);
   const [success, setSuccess] = useState(false);
+  // W4: Track lastModified for optimistic locking
+  const lastModifiedRef = useRef<number | undefined>(undefined);
 
   const fetchConfig = useCallback(async () => {
     const controller = new AbortController();
@@ -37,6 +40,8 @@ export function useThinkingConfig() {
       if (!res.ok) throw new Error('Failed to load Thinking config');
       const data = await res.json();
       setConfig(data.config || DEFAULT_THINKING_CONFIG);
+      // W4: Store lastModified for optimistic locking
+      lastModifiedRef.current = data.lastModified;
     } catch (err) {
       clearTimeout(timeoutId);
       if ((err as Error).name === 'AbortError') {
@@ -63,10 +68,16 @@ export function useThinkingConfig() {
         setSaving(true);
         setError(null);
 
+        // W4: Include lastModified for optimistic locking
+        const payload = {
+          ...optimisticConfig,
+          lastModified: lastModifiedRef.current,
+        };
+
         const res = await fetch('/api/thinking', {
           method: 'PUT',
           headers: { 'Content-Type': 'application/json' },
-          body: JSON.stringify(optimisticConfig),
+          body: JSON.stringify(payload),
           signal: controller.signal,
         });
 
@@ -74,11 +85,17 @@ export function useThinkingConfig() {
 
         if (!res.ok) {
           const data = await res.json();
+          // W4: Handle conflict (409) with user-friendly message
+          if (res.status === 409) {
+            throw new Error('Config changed by another session. Refreshing...');
+          }
           throw new Error(data.error || 'Failed to save');
         }
 
         const data = await res.json();
         setConfig(data.config);
+        // W4: Update lastModified after successful save
+        lastModifiedRef.current = data.lastModified;
         setSuccess(true);
         setTimeout(() => setSuccess(false), 1500);
       } catch (err) {
@@ -88,12 +105,16 @@ export function useThinkingConfig() {
           setError('Request timeout - please try again');
         } else {
           setError((err as Error).message);
+          // W4: On conflict, auto-refresh to get latest
+          if ((err as Error).message.includes('another session')) {
+            setTimeout(() => fetchConfig(), 1000);
+          }
         }
       } finally {
         setSaving(false);
       }
     },
-    [config]
+    [config, fetchConfig]
   );
 
   const setMode = useCallback(

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

@@ -16,7 +16,7 @@ import {
   SelectTrigger,
   SelectValue,
 } from '@/components/ui/select';
-import { RefreshCw, CheckCircle2, AlertCircle, Brain } from 'lucide-react';
+import { RefreshCw, CheckCircle2, AlertCircle, Brain, Info } from 'lucide-react';
 import { useThinkingConfig } from '../../hooks';
 import type { ThinkingMode } from '../../types';
 
@@ -69,8 +69,22 @@ export default function ThinkingSection() {
       >
         {error && (
           <Alert variant="destructive" className="py-2 shadow-lg">
-            <AlertCircle className="h-4 w-4" />
-            <AlertDescription>{error}</AlertDescription>
+            <div className="flex items-center justify-between w-full">
+              <div className="flex items-center gap-2">
+                <AlertCircle className="h-4 w-4" />
+                <AlertDescription>{error}</AlertDescription>
+              </div>
+              {/* W1: Retry button on error */}
+              <Button
+                variant="outline"
+                size="sm"
+                onClick={fetchConfig}
+                className="h-7 px-2 text-xs border-destructive/50 hover:bg-destructive/10"
+              >
+                <RefreshCw className="w-3 h-3 mr-1" />
+                Retry
+              </Button>
+            </div>
           </Alert>
         )}
         {success && (
@@ -91,6 +105,19 @@ export default function ThinkingSection() {
             </p>
           </div>
 
+          {/* U4: Provider support indicator */}
+          <div className="flex items-start gap-2 p-3 rounded-lg bg-blue-50 dark:bg-blue-900/20 border border-blue-200 dark:border-blue-800">
+            <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>
+            </div>
+          </div>
+
           {/* Mode Selection */}
           <div className="space-y-3">
             <h3 className="text-base font-medium">Thinking Mode</h3>