diff --git a/tests/boundary/mcp/contractPresentation.test.ts b/tests/boundary/mcp/contractPresentation.test.ts
index 2a3c9f7ec..9d1d9d6bb 100644
--- a/tests/boundary/mcp/contractPresentation.test.ts
+++ b/tests/boundary/mcp/contractPresentation.test.ts
@@ -1,10 +1,12 @@
 import { execFile } from "node:child_process";
 import { fileURLToPath } from "node:url";
 import { promisify } from "node:util";
+import { isCallToolResult } from "@modelcontextprotocol/server";
 import { expect, it } from "vitest";
 import { z } from "zod";
 
 import { GENERATED_MCP_TOOL_CATALOG } from "../../fixtures/mcpToolCatalog.js";
+import { parseMcpToolError } from "../../fixtures/mcpToolError.js";
 
 const execute = promisify(execFile);
 const fixture = fileURLToPath(
@@ -41,6 +43,8 @@ it("preserves advertised schemas and handler meaning when presentation order cha
     expect(advertised.outputSchema).toEqual(canonical?.outputSchema);
   }
   for (const { name, response } of result.responses) {
+    if (!isCallToolResult(response))
+      throw new Error(`Invalid tools/call fixture result for ${name}`);
     if (name === "reconcile_javascript_runtime") {
       expect(response.isError).not.toBe(true);
       expect(response.structuredContent).toMatchObject({
@@ -48,7 +52,7 @@ it("preserves advertised schemas and handler meaning when presentation order cha
       });
     } else {
       expect(response.isError, name).toBe(true);
-      expect(response.structuredContent, name).toMatchObject({
+      expect(parseMcpToolError(response), name).toMatchObject({
         error: { details: { operation: name } },
       });
     }
diff --git a/tests/boundary/mcp/largeToolResult.test.ts b/tests/boundary/mcp/largeToolResult.test.ts
index 76122951a..00afa2d7a 100644
--- a/tests/boundary/mcp/largeToolResult.test.ts
+++ b/tests/boundary/mcp/largeToolResult.test.ts
@@ -25,6 +25,7 @@ import { registerOfficialTools } from "../../../src/server/registerOfficialTools
 import { ToolResultDelivery } from "../../../src/server/toolResult.js";
 import { EvidenceMcpServer } from "../../../src/server/EvidenceMcpServer.js";
 import { encodeToolResult } from "../../../src/server/toolResultEncoding.js";
+import { parseMcpToolError } from "../../fixtures/mcpToolError.js";
 
 const delivery = new ToolResultDelivery(STDIO_DEFAULT_MAX_BUFFER_SIZE);
 
@@ -188,7 +189,7 @@ describe("large complete Evidence MCP delivery", () => {
           }),
         }),
       })
-      .parse(result.structuredContent).error.details.reported_limits;
+      .parse(parseMcpToolError(result)).error.details.reported_limits;
     const retained = parseEvidence(
       records.get(limits.evidence_reference.evidence_id),
     );