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fix(server): prevent preview_snapshot from bricking sessions with oversized images #11624

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fix(server): prevent preview_snapshot from bricking sessions with oversized images #11624

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8 changes: 7 additions & 1 deletion apps/server/src/mcp/McpHttpServer.test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -257,7 +257,13 @@ it.effect("registers annotated tools and preserves authenticated request context
Effect.provideService(McpSchema.McpServerClient, client),
);
expect(snapshot.isError).toBe(false);
expect(snapshot.content.some((content) => content.type === "image")).toBe(true);
// Regression #11295: inline image content was removed from snapshot
// results because full-resolution base64 PNGs in tool history brick
// sessions when providers reject inline images.
expect(snapshot.content.some((content) => content.type === "image")).toBe(false);
expect(snapshot.content).toEqual([
{ type: "text", text: expect.any(String) },
]);
expect(snapshot.structuredContent).toMatchObject({
screenshot: { mimeType: "image/png", width: 10, height: 5 },
});
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16 changes: 8 additions & 8 deletions apps/server/src/mcp/McpHttpServer.ts
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Expand Up @@ -182,18 +182,18 @@ const registerPreviewSnapshot = Effect.fn("McpHttpServer.registerPreviewSnapshot
height: screenshot.height,
},
};
// Screenshot pixel data is deliberately excluded from the MCP
// tool result. Embedding full-resolution base64 PNGs in tool
// history bricks sessions when providers reject inline images —
// the oversized payload cannot be removed from history and every
// subsequent turn fails. The structured content already carries
// screenshot dimensions and mime type for reference; the client
// preview renders the actual image from its own copy.
return Effect.succeed(
new McpSchema.CallToolResult({
isError: false,
structuredContent: metadata,
content: [
{ type: "text", text: JSON.stringify(metadata) },
{
type: "image",
data: new Uint8Array(Buffer.from(screenshot.data, "base64")),
mimeType: screenshot.mimeType,
},
],
content: [{ type: "text", text: JSON.stringify(metadata) }],

@chatgpt-codex-connector chatgpt-codex-connector Bot Sep 13, 2026

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P1 Badge Return a bounded screenshot to image-capable providers

For providers/models that accept MCP image blocks, every preview_snapshot now returns only page metadata, so pages whose relevant state is visual-only (canvas output, layout defects, video frames, or other non-semantic content) can no longer be inspected by the agent even though PreviewSnapshotTool still promises a PNG screenshot. The client preview's copy is visible to the user, not to the provider consuming this MCP response; preserve a size-bounded/downscaled image for compatible providers, or omit it only for adapters that cannot accept one.

AGENTS.md reference: AGENTS.md:L69-L72

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}),
);
},
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