fix(core): omit inline image data from compaction prompt

packages/core/src/prompt.ts

@@ -293,14 +293,49 @@ export function getSystemPrompt(_projectRoot: string, options: PromptToolOptions
   return toolDocs ? `${SYSTEM_PROMPT_BASE}\n\n# Available Tools\n\n${toolDocs}` : SYSTEM_PROMPT_BASE;
 }
 
+const OMITTED_IMAGE_DATA_URL = "[image data omitted from compaction prompt]";
+
+function compactContentParams(contentParams: unknown): unknown {
+  if (!contentParams) {
+    return contentParams;
+  }
+
+  const compactPart = (part: unknown): unknown => {
+    if (!part || typeof part !== "object") {
+      return part;
+    }
+    const candidate = part as { type?: unknown; image_url?: unknown };
+    if (candidate.type !== "image_url") {
+      return part;
+    }
+    const imageUrl = candidate.image_url;
+    if (!imageUrl || typeof imageUrl !== "object") {
+      return part;
+    }
+    const url = (imageUrl as { url?: unknown }).url;
+    if (typeof url !== "string" || !url.startsWith("data:")) {
+      return part;
+    }
+    return {
+      ...candidate,
+      image_url: {
+        ...(imageUrl as Record<string, unknown>),
+        url: OMITTED_IMAGE_DATA_URL,
+      },
+    };
+  };
+
+  return Array.isArray(contentParams) ? contentParams.map(compactPart) : compactPart(contentParams);
+}
+
 export function getCompactPrompt(sessionMessages: SessionMessage[]): string {
   const jsonl = sessionMessages
     .map((message) =>
       JSON.stringify({
         id: message.id,
         role: message.role,
         content: message.content,
-        contentParams: message.contentParams,
+        contentParams: compactContentParams(message.contentParams),
         messageParams: message.messageParams,
         createTime: message.createTime,
       })

packages/core/src/tests/prompt.test.ts

@@ -7,11 +7,13 @@ import { fileURLToPath } from "url";
 import {
   buildSkillCatalogPrompt,
   buildSkillDocumentsPrompt,
+  getCompactPrompt,
   getPlanModePrompt,
   getRuntimeContext,
   getSystemPrompt,
   getTools,
 } from "../prompt";
+import type { SessionMessage } from "../session";
 
 const repoRoot = path.resolve(path.dirname(fileURLToPath(import.meta.url)), "../..");
 const tempDirs: string[] = [];
@@ -323,3 +325,42 @@ test("deepseek-flash uses native image tools unless multimodal is disabled", ()
     assert.equal(prompt.includes("## UnderstandImage"), !native);
   }
 });
+
+test("getCompactPrompt omits inline image data payloads", () => {
+  const buildMessage = (overrides: Partial<SessionMessage>): SessionMessage => ({
+    id: "message",
+    sessionId: "session",
+    role: "user",
+    content: null,
+    contentParams: null,
+    messageParams: null,
+    compacted: false,
+    visible: true,
+    createTime: "2026-01-01T00:00:00.000Z",
+    updateTime: "2026-01-01T00:00:00.000Z",
+    ...overrides,
+  });
+
+  const prompt = getCompactPrompt([
+    buildMessage({
+      id: "inline",
+      content: "inline screenshot",
+      contentParams: [
+        {
+          type: "image_url",
+          image_url: { url: "data:image/png;base64,AAAA", detail: "high" },
+        },
+      ],
+    }),
+    buildMessage({
+      id: "remote",
+      content: "remote screenshot",
+      contentParams: [{ type: "image_url", image_url: { url: "https://example.com/a.png" } }],
+    }),
+  ]);
+
+  assert.equal(prompt.includes("data:image"), false);
+  assert.equal(prompt.includes("[image data omitted from compaction prompt]"), true);
+  assert.equal(prompt.includes("https://example.com/a.png"), true);
+  assert.equal(prompt.includes('"detail":"high"'), true);
+});