fix(wechat): scrub image_url from sessions and harden vision handoff.

Strip image_url from persisted session payloads, keep image turns scoped to the active request, and align proxy/vision/page-data paths so WeChat image history does not leak into fresh sessions.

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

chat-image-turn-scope.test.mjs

@@ -2,6 +2,7 @@ import assert from 'node:assert/strict';
 import test from 'node:test';
 import {
   buildCurrentTurnImageScopeNote,
+  conversationHasImageUrlContent,
   dedupeImageUrlsByAssetKey,
   extractCurrentTurnImageUrls,
   scrubConversationHistoricalImageAttachments,
@@ -113,3 +114,46 @@ test('buildCurrentTurnImageScopeNote states one independent topic per upload', (
   assert.match(note, /不得与历史轮次混用/);
   assert.match(note, /asset=asset-9/);
 });
+
+test('conversationHasImageUrlContent detects historical poison and ignores active turn', () => {
+  const conversation = [
+    {
+      id: 'assistant-old',
+      role: 'assistant',
+      content: [
+        { type: 'text', text: '看图' },
+        { type: 'image_url', image_url: { url: 'https://example.com/old.png' } },
+      ],
+    },
+    {
+      id: 'user-new',
+      role: 'user',
+      content: [
+        { type: 'text', text: '这是什么' },
+        { type: 'image_url', image_url: { url: 'https://example.com/new.png' } },
+      ],
+    },
+  ];
+
+  assert.equal(conversationHasImageUrlContent(conversation), true);
+  assert.equal(
+    conversationHasImageUrlContent(conversation, { excludeMessageId: 'user-new' }),
+    true,
+  );
+  assert.equal(
+    conversationHasImageUrlContent(
+      [
+        {
+          id: 'user-new',
+          role: 'user',
+          content: [
+            { type: 'text', text: '这是什么' },
+            { type: 'image_url', image_url: { url: 'https://example.com/new.png' } },
+          ],
+        },
+      ],
+      { excludeMessageId: 'user-new' },
+    ),
+    false,
+  );
+});