diff --git a/docs/cli.md b/docs/cli.md
index 76dde4f4fb..5b075fe373 100644
--- a/docs/cli.md
+++ b/docs/cli.md
@@ -301,6 +301,14 @@ user permissions; consult the chosen guide for host requirements and effects.
 
 ## Output and exit status
 
+`rea mcp doctor --json` checks production MCP startup and reports child logs in
+`diagnostics`. It drains stderr while retaining at most its first 64 KiB of raw
+bytes as text, omitting a final UTF-8 code point if it crosses that byte limit.
+`stderr_bytes` counts all observed bytes, including omitted output;
+`stderr_truncated` indicates that output exceeded the retention limit. The same
+diagnostics appear inside the report when `--full-output` is selected. Log
+truncation alone does not change the diagnostic health or exit status.
+
 The default terminal format is TOON. Use `--json` when saving results for a
 JSON consumer. `--json` is indented on a terminal and compact when piped or
 redirected, which keeps large results smaller for agents and scripts; pipe
diff --git a/tests/boundary/browser/cdpBrowserProvider.lifecycle_failures.test.ts b/tests/boundary/browser/cdpBrowserProvider.lifecycle_failures.test.ts
index 7c0d07445e..01b1f54da6 100644
--- a/tests/boundary/browser/cdpBrowserProvider.lifecycle_failures.test.ts
+++ b/tests/boundary/browser/cdpBrowserProvider.lifecycle_failures.test.ts
@@ -1,10 +1,11 @@
-import { describe, expect, it } from "vitest";
+import { describe, expect, it, vi } from "vitest";
 
 import { CdpBrowserProvider } from "../../../src/browser/CdpBrowserProvider.js";
 import {
   inspectWebPageInputSchema,
   listBrowserTargetsInputSchema,
 } from "../../../src/domain/browserObservation.js";
+import { AnalysisInputError } from "../../../src/domain/analysisErrorCore.js";
 import { analyzeWebBundleInputSchema } from "../../../src/domain/webBundleAnalysis.js";
 import { observeWebSessionInputSchema } from "../../../src/domain/browserSession.js";
 import {
@@ -514,6 +515,71 @@ describe("CdpBrowserProvider: navigation commit and target identity", () => {
   });
 });
 
+describe("CdpBrowserProvider: source-map cancellation", () => {
+  it("classifies an AnalysisError abort reason as cancellation", async () => {
+    const browser = await startFakeCdpBrowser({
+      sourceMapBody: JSON.stringify({
+        version: 3,
+        sources: ["app.ts"],
+        names: [],
+        mappings: "",
+      }),
+    });
+    trackBrowser(browser);
+    const controller = new AbortController();
+    const reason = new AnalysisInputError("caller_operation");
+    let markSourceMapRequested!: () => void;
+    const sourceMapRequested = new Promise<void>((resolve) => {
+      markSourceMapRequested = resolve;
+    });
+    const originalFetch = globalThis.fetch;
+    const fetchMock = vi
+      .spyOn(globalThis, "fetch")
+      .mockImplementation((resource, init) => {
+        if (String(resource).includes("/app.js.map")) {
+          markSourceMapRequested();
+          return new Promise<Response>((_resolve, reject) => {
+            const signal = init?.signal;
+            if (signal?.aborted === true) {
+              reject(signal.reason);
+              return;
+            }
+            signal?.addEventListener("abort", () => reject(signal.reason), {
+              once: true,
+            });
+          });
+        }
+        return originalFetch(resource, init);
+      });
+    try {
+      const pending = new CdpBrowserProvider().analyzeBundle(
+        analyzeWebBundleInputSchema.parse({
+          cdp_endpoint: browser.endpoint,
+          allowed_origins: [browser.allowedOrigin],
+          target_id: "allowed-page",
+          observation_ms: 0,
+          fetch_source_maps: true,
+        }),
+        { signal: controller.signal },
+      );
+      await sourceMapRequested;
+      controller.abort(reason);
+      const result = await pending;
+      expect(result).toMatchObject({
+        ok: false,
+        error: {
+          _tag: "AnalysisCancelledError",
+          operation: "analyze_web_bundle",
+        },
+      });
+      if (result.ok) throw new Error("Expected source-map cancellation");
+      expect(result.error.cause).toBe(reason);
+    } finally {
+      fetchMock.mockRestore();
+    }
+  });
+});
+
 const waitForCommand = async (
   browser: FakeCdpBrowser,
   method: string,
diff --git a/tests/boundary/mcp/navigationContextMcp.test.ts b/tests/boundary/mcp/navigationContextMcp.test.ts
new file mode 100644
index 0000000000..7bcf1d363d
--- /dev/null
+++ b/tests/boundary/mcp/navigationContextMcp.test.ts
@@ -0,0 +1,60 @@
+import { Client, InMemoryTransport } from "@modelcontextprotocol/client";
+import type { CallToolResult } from "@modelcontextprotocol/server";
+import { expect, it } from "vitest";
+
+import { ok } from "../../../src/domain/result.js";
+import { createServer } from "../../../src/server/createServer.js";
+import { observed } from "../../fixtures/analysisExecution.js";
+import { createTestBinarySession } from "../../fixtures/binarySession.js";
+import { parseMcpToolError } from "../../fixtures/mcpToolError.js";
+
+const navigate = async (
+  selection: Readonly<Record<string, unknown>>,
+): Promise<CallToolResult> => {
+  const session = createTestBinarySession(() => ({
+    execute: (operation) =>
+      Promise.resolve(observed(selection[operation] ?? null)),
+    close: () => Promise.resolve(ok(null)),
+  }));
+  const server = createServer({ kind: "session", session });
+  const client = new Client({ name: "navigation-test", version: "1" });
+  const [clientTransport, serverTransport] =
+    InMemoryTransport.createLinkedPair();
+  try {
+    await server.connect(serverTransport);
+    await client.connect(clientTransport);
+    await client.callTool({
+      name: "open_binary",
+      arguments: { path: process.execPath },
+    });
+    return (await client.callTool({
+      name: "get_navigation_context",
+      arguments: {},
+    })) as CallToolResult;
+  } finally {
+    await Promise.allSettled([client.close(), server.close(), session.close()]);
+  }
+};
+
+it.each([
+  {
+    selection: { current_document: null, current_address: "0x401000" },
+    operation: "current_document",
+  },
+  {
+    selection: { current_document: "fixture", current_address: null },
+    operation: "current_address",
+  },
+])(
+  "delivers a typed MCP failure when $operation is not a string",
+  async ({ selection, operation }) => {
+    const result = await navigate(selection);
+    expect(JSON.stringify(result.content)).not.toContain(
+      "Output validation error",
+    );
+    expect(parseMcpToolError(result).error).toMatchObject({
+      code: "unreadable_output",
+      details: { operation },
+    });
+  },
+);