fix(vision): stop read_image from poisoning text-provider sessions

Image turns already get a vision-model description injected into the prompt,
but the agent kept calling read_image to "confirm" the pictures. Those tool
results carry base64 image parts that Goose persists, so every later turn
against the text-only chat provider failed with `unknown variant image_url`
before the agent could write the page. WeChat page requests therefore fell
through to the fail-closed delivery message.

Drop read_image for the turn whenever a vision model handles the images, say
so explicitly in the injected prompt, and teach the poison scan to recognise
tool image parts so already-polluted sessions rotate instead of failing again.

Co-authored-by: Cursor <cursoragent@cursor.com>

wechat-mp.mjs

@@ -85,7 +85,10 @@ import { resolveMindSpaceUserPublishDir } from './mindspace-runtime-config.mjs';
 import {
   buildPageDataCollectFailureText,
 } from './mindspace-page-data-finish-guard.mjs';
-import { conversationHasImageUrlContent } from './chat-image-turn-scope.mjs';
+import {
+  conversationHasImageUrlContent,
+  conversationHasToolImageContent,
+} from './chat-image-turn-scope.mjs';
 
 export { buildWechatAgentPrompt };
 
@@ -2450,12 +2453,20 @@ export function createWechatMpService({
       }
       const payload = await readJsonResponse(response);
       const conversation = Array.isArray(payload?.conversation) ? payload.conversation : [];
-      if (!conversationHasImageUrlContent(conversation)) {
+      const hasImageUrlContent = conversationHasImageUrlContent(conversation);
+      // REGRESSION GUARD: vision-turn-read-image-isolation — read_image leaves
+      // base64 image parts inside tool responses instead of image_url. Goose
+      // keeps them, so the next turn against a text-only chat provider fails
+      // before the agent can write any page.
+      const hasToolImageContent = conversationHasToolImageContent(conversation);
+      if (!hasImageUrlContent && !hasToolImageContent) {
         return { sessionId, carriedSessionContent, rotated: false };
       }
       logger.warn?.('WeChat MP rotating image-polluted agent session before reply:', {
         agentSessionId: sessionId,
         conversationLength: conversation.length,
+        hasImageUrlContent,
+        hasToolImageContent,
       });
       const nextRoute = await ensureWechatAgentSession({
         userId,