fix: recover WeChat page thumbnail delivery

mindspace-image-generation.mjs

@@ -13,6 +13,29 @@ function htmlSrcForWorkspaceAsset(workspaceRelativePath) {
   return normalized.slice('public/'.length) || null;
 }
 
+const IMAGE_MAKE_IDEMPOTENCY_KEY_MAX_LENGTH = 128;
+const WECHAT_PAGE_THUMBNAIL_KEY_PATTERN = /^wechat-[a-zA-Z0-9._-]+-page-\d+-thumbnail$/;
+
+function boundedIdempotencyKey(base, suffix = '') {
+  const normalizedBase = String(base ?? '').trim();
+  const normalizedSuffix = String(suffix ?? '');
+  return `${normalizedBase.slice(0, Math.max(0, IMAGE_MAKE_IDEMPOTENCY_KEY_MAX_LENGTH - normalizedSuffix.length))}${normalizedSuffix}`;
+}
+
+function resolveImageMakeIdempotencyKey({ idempotencyKey, purpose, prompt, negativePrompt }) {
+  const normalized = String(idempotencyKey ?? '').trim();
+  if (!normalized) return `imgreq_${crypto.randomUUID()}`;
+  if (purpose !== 'hero' || !WECHAT_PAGE_THUMBNAIL_KEY_PATTERN.test(normalized)) {
+    return normalized;
+  }
+  const promptHash = crypto
+    .createHash('sha256')
+    .update([purpose, String(prompt ?? '').trim(), String(negativePrompt ?? '').trim()].join('\0'))
+    .digest('hex')
+    .slice(0, 12);
+  return boundedIdempotencyKey(normalized, `-p-${promptHash}`);
+}
+
 function resolvePurposeDimensions(spec, env, logger) {
   const widthKey = `IMAGE_MAKE_${spec.envPrefix}_WIDTH`;
   const heightKey = `IMAGE_MAKE_${spec.envPrefix}_HEIGHT`;
@@ -65,7 +88,12 @@ export function createMindSpaceImageGenerationService({
       const maxAttempts = Number.isFinite(configuredAttempts)
         ? Math.max(1, Math.min(3, Math.floor(configuredAttempts)))
         : 3;
-      const baseIdempotencyKey = idempotencyKey || `imgreq_${crypto.randomUUID()}`;
+      const baseIdempotencyKey = resolveImageMakeIdempotencyKey({
+        idempotencyKey,
+        purpose,
+        prompt,
+        negativePrompt,
+      });
       let generated = null;
       let acceptedReview = null;
       let retryFeedback = '';
@@ -76,7 +104,7 @@ export function createMindSpaceImageGenerationService({
           : prompt;
         const attemptKey = attempt === 1
           ? baseIdempotencyKey
-          : `${baseIdempotencyKey.slice(0, 160)}-review-${attempt}`;
+          : boundedIdempotencyKey(baseIdempotencyKey, `-review-${attempt}`);
         generated = await imageMakeClient.generateImage({
           prompt: attemptPrompt,
           negativePrompt,