fix(agents): coerce non-text/image MCP tool-result blocks to text (fixes #90710) (#90728)

849261680 · clawsweeper[bot] · Takhoffman · web-flow · commit b1e4b6b65e2c · 2026-06-06T02:16:10.000Z
Summary: - The PR converts wider MCP CallToolResult content blocks into text/image AgentToolResult blocks at the bundle-MCP materialization boundary and adds regression tests. - PR surface: Source +36, Tests +66. Total +102 across 2 files. - Reproducibility: yes. Source inspection shows current main lets MCP resource/audio blocks cross into a text/ ... a spawned stdio MCP server; I did not run a live hosted Anthropic API round trip in this read-only review. Automerge notes: - No ClawSweeper repair was needed after automerge opt-in. Validation: - ClawSweeper review passed for head f70dccf. - Required merge gates passed before the squash merge. Prepared head SHA: f70dccf Review: #90728 (comment) Co-authored-by: 宇宙熊Yzx <53250620+849261680@users.noreply.github.com> Co-authored-by: clawsweeper[bot] <274271284+clawsweeper[bot]@users.noreply.github.com> Approved-by: takhoffman Co-authored-by: takhoffman <781889+takhoffman@users.noreply.github.com>
diff --git a/src/agents/agent-bundle-mcp-materialize.ts b/src/agents/agent-bundle-mcp-materialize.ts
@@ -1,6 +1,6 @@
 /** Materializes configured MCP catalog entries into agent tools and runtime helpers. */
 import crypto from "node:crypto";
-import type { CallToolResult } from "@modelcontextprotocol/sdk/types.js";
+import type { CallToolResult, ContentBlock } from "@modelcontextprotocol/sdk/types.js";
 import { normalizeLowercaseStringOrEmpty } from "@openclaw/normalization-core/string-coerce";
 import type { OpenClawConfig } from "../config/types.openclaw.js";
 import { logWarn } from "../logger.js";
@@ -20,13 +20,49 @@ import { normalizeToolParameterSchema } from "./agent-tools-parameter-schema.js"
 import type { AgentToolResult } from "./runtime/index.js";
 import type { AnyAgentTool } from "./tools/common.js";
 
+type ToolResultContentBlock = AgentToolResult<unknown>["content"][number];
+
+// AgentToolResult only carries text/image, but an MCP CallToolResult can also
+// return resource_link, resource, and audio blocks (MCP SDK ContentBlock union).
+// Coercing those into the text/image contract here keeps the boundary honest so
+// downstream provider converters never build an image block with undefined
+// data/media_type, which makes Anthropic 400 and poisons the whole session
+// history (every later turn replays the bad block and 400s too). See #90710.
+function mcpContentBlockToToolResult(block: ContentBlock): ToolResultContentBlock {
+  switch (block.type) {
+    case "text":
+      return { type: "text", text: block.text };
+    case "image":
+      // Only emit an image when the base64 source is actually present.
+      if (block.data && block.mimeType) {
+        return { type: "image", data: block.data, mimeType: block.mimeType };
+      }
+      return { type: "text", text: JSON.stringify(block) };
+    case "audio":
+      return { type: "text", text: `[audio ${block.mimeType}]` };
+    case "resource_link": {
+      const label = block.title ?? block.name;
+      return { type: "text", text: label ? `[${label}] ${block.uri}` : block.uri };
+    }
+    case "resource": {
+      const resource = block.resource;
+      const text = "text" in resource ? resource.text : undefined;
+      return { type: "text", text: text ?? resource.uri };
+    }
+    default:
+      // Forward-compat / untrusted-server guard: stringify any block type the
+      // installed MCP SDK union does not cover instead of dropping it.
+      return { type: "text", text: JSON.stringify(block) };
+  }
+}
+
 function toAgentToolResult(params: {
   serverName: string;
   toolName: string;
   result: CallToolResult;
 }): AgentToolResult<unknown> {
-  const content = Array.isArray(params.result.content)
-    ? (params.result.content as AgentToolResult<unknown>["content"])
+  const content: AgentToolResult<unknown>["content"] = Array.isArray(params.result.content)
+    ? params.result.content.map(mcpContentBlockToToolResult)
     : [];
   const structuredContentBlock =
     params.result.structuredContent !== undefined
diff --git a/src/agents/agent-bundle-mcp-tools.materialize.test.ts b/src/agents/agent-bundle-mcp-tools.materialize.test.ts
@@ -156,6 +156,72 @@ describe("createBundleMcpToolRuntime", () => {
     });
   });
 
+  it("coerces non-text/image MCP tool-result blocks to text (resource_link/resource/audio)", async () => {
+    // resource_link/resource/audio blocks have no base64 image source; if they
+    // leaked into the provider image branch Anthropic would 400 on an image with
+    // undefined data/media_type and poison the whole session history (#90710).
+    const runtime = await materializeBundleMcpToolsForRun({
+      runtime: makeToolRuntime({
+        result: {
+          content: [
+            { type: "text", text: "intro" },
+            {
+              type: "resource_link",
+              uri: "https://example.com/a.docx",
+              name: "a.docx",
+              title: "Quarterly report",
+            },
+            {
+              type: "resource_link",
+              uri: "https://example.com/bare",
+              name: "",
+            },
+            {
+              type: "resource",
+              resource: { uri: "memo://one", text: "memo body" },
+            },
+            {
+              type: "resource",
+              resource: { uri: "blob://two", blob: "AAAA", mimeType: "application/pdf" },
+            },
+            { type: "audio", data: "AAAA", mimeType: "audio/mpeg" },
+            { type: "image", data: "iVBOR", mimeType: "image/png" },
+          ],
+          isError: false,
+        } as CallToolResult,
+      }),
+    });
+
+    const result = await runtime.tools[0].execute("call-bundle-probe", {}, undefined, undefined);
+
+    expect(result.content).toEqual([
+      { type: "text", text: "intro" },
+      { type: "text", text: "[Quarterly report] https://example.com/a.docx" },
+      { type: "text", text: "https://example.com/bare" },
+      { type: "text", text: "memo body" },
+      { type: "text", text: "blob://two" },
+      { type: "text", text: "[audio audio/mpeg]" },
+      { type: "image", data: "iVBOR", mimeType: "image/png" },
+    ]);
+  });
+
+  it("coerces a malformed image block (missing base64 source) to text", async () => {
+    // A real-world poison case: image block with undefined data/media_type.
+    const runtime = await materializeBundleMcpToolsForRun({
+      runtime: makeToolRuntime({
+        result: {
+          content: [{ type: "image" } as unknown as CallToolResult["content"][number]],
+          isError: false,
+        } as CallToolResult,
+      }),
+    });
+
+    const result = await runtime.tools[0].execute("call-bundle-probe", {}, undefined, undefined);
+
+    expect(result.content).toHaveLength(1);
+    expect(result.content[0]).toEqual({ type: "text", text: JSON.stringify({ type: "image" }) });
+  });
+
   it("disambiguates bundle MCP tools that collide with existing tool names", async () => {
     const runtime = await materializeBundleMcpToolsForRun({
       runtime: makeToolRuntime(),
