diff --git a/packages/cli/tests/launch-timeout.test.ts b/packages/cli/tests/launch-timeout.test.ts
new file mode 100644
index 000000000..580a56ee4
--- /dev/null
+++ b/packages/cli/tests/launch-timeout.test.ts
@@ -0,0 +1,61 @@
+/**
+ * The harness deadline in `@executablemd/test-support/launch`.
+ *
+ * `runCli` bounds every suite's `xmd` subprocess, and its deadline expires
+ * under host contention rather than by the child's own doing — so when it
+ * does, the failure it raises is the only record the suite gets of that run.
+ * This proves the record carries what a diagnosis needs: the deadline, and
+ * whatever the child wrote on each channel before the run was abandoned.
+ */
+
+import { describe, it } from "@executablemd/test-support/bdd";
+import { expect } from "@executablemd/test-support/expect";
+import { ensure, scoped } from "effection";
+import type { Operation } from "effection";
+import { ensureDir, rm, writeTextFile } from "@effectionx/fs";
+import { randomUUID } from "node:crypto";
+import { join } from "node:path";
+import { tmpdir } from "node:os";
+import { cliRuntime, runCli } from "@executablemd/test-support/launch";
+
+// The deadline must expire for the failure to exist, so this test always costs
+// its whole limit — kept as small as the slowest host launch leaves safe.
+const LIMIT = cliRuntime() === "node" ? 20_000 : 10_000;
+
+/** Says its name on each channel, then outlives the deadline. */
+const LINGERING = [
+  "# Lingering",
+  "",
+  "```bash exec",
+  "printf 'lingering-out'; printf 'lingering-err' >&2; sleep 120",
+  "```",
+  "",
+].join("\n");
+
+/** A directory holding the document, with no repository behind it. */
+function useDocument<T>(body: (dir: string) => Operation<T>): Operation<T> {
+  return scoped(function* () {
+    const dir = join(tmpdir(), `xmd-deadline-${randomUUID()}`);
+    yield* ensure(() => rm(dir, { recursive: true, force: true }));
+    yield* ensureDir(dir);
+    yield* writeTextFile(join(dir, "lingering.md"), LINGERING);
+    return yield* body(dir);
+  });
+}
+
+describe("Harness deadline — an abandoned xmd run keeps its account", () => {
+  it("the failure names the deadline and carries both channels", function* () {
+    yield* useDocument(function* (dir) {
+      let failure: Error | undefined;
+      try {
+        yield* runCli(["run", "lingering.md"], { cwd: dir, timeout: LIMIT }).join();
+      } catch (error) {
+        failure = error as Error;
+      }
+
+      expect(failure?.message).toContain(`timed out after ${LIMIT}ms`);
+      expect(failure?.message).toContain("lingering-out");
+      expect(failure?.message).toContain("lingering-err");
+    });
+  });
+});
diff --git a/packages/test-support/launch.ts b/packages/test-support/launch.ts
index c5b48f0b9..3fa6b528e 100644
--- a/packages/test-support/launch.ts
+++ b/packages/test-support/launch.ts
@@ -1,7 +1,9 @@
 import { exec } from "@effectionx/process";
 import type { ProcessResult } from "@effectionx/process";
 import { timebox } from "@effectionx/timebox";
+import { spawn } from "effection";
 import type { Operation } from "effection";
+import { loadavg } from "node:os";
 import { join } from "node:path";
 import process from "node:process";
 import { fileURLToPath } from "node:url";
@@ -83,33 +85,83 @@ export interface CliRun {
  */
 export function runCli(args: string[], options: CliRunOptions = {}): CliRun {
   return {
-    join: () => bounded(args, options, (run) => run.join()),
-    expect: () => bounded(args, options, (run) => run.expect()),
+    join: () => bounded(args, options, "join"),
+    expect: () => bounded(args, options, "expect"),
   };
 }
 
+/** Everything the child wrote on one channel before its run settled. */
+interface PartialOutput {
+  stdout: string;
+  stderr: string;
+}
+
 function* bounded(
   args: string[],
   options: CliRunOptions,
-  settle: (run: ReturnType<typeof exec>) => Operation<ProcessResult>,
+  mode: "join" | "expect",
 ): Operation<ProcessResult> {
   const limit = options.timeout ?? DEFAULT_TIMEOUT;
+  const cli = cliCommand(args);
+  // Accumulated outside the deadline, so a run the deadline abandons still has
+  // an account: a timeout that reports nothing but its duration cannot say
+  // whether the child hung before its first line or after its last.
+  const partial: PartialOutput = { stdout: "", stderr: "" };
   const result = yield* timebox<ProcessResult>(limit, function* () {
-    const cli = cliCommand(args);
-    return yield* settle(
-      exec(cli.command, {
-        arguments: cli.arguments,
-        cwd: options.cwd,
-        env: cliEnv(options),
-      }),
-    );
+    const child = yield* exec(cli.command, {
+      arguments: cli.arguments,
+      cwd: options.cwd,
+      env: cliEnv(options),
+    });
+    yield* spawn(function* () {
+      const output = yield* child.stdout;
+      for (let next = yield* output.next(); !next.done; next = yield* output.next()) {
+        partial.stdout += text(next.value);
+      }
+    });
+    yield* spawn(function* () {
+      const output = yield* child.stderr;
+      for (let next = yield* output.next(); !next.done; next = yield* output.next()) {
+        partial.stderr += text(next.value);
+      }
+    });
+    const status = yield* mode === "expect" ? child.expect() : child.join();
+    return { ...status, stdout: partial.stdout, stderr: partial.stderr };
   });
   if (result.timeout) {
-    throw new Error(`xmd ${args.join(" ")} timed out after ${limit}ms`);
+    throw new Error(abandonedReport(args, limit, partial));
   }
   return result.value;
 }
 
+// Chunks decode independently, exactly as capture concatenates them.
+function text(bytes: Uint8Array): string {
+  return new TextDecoder().decode(bytes);
+}
+
+/**
+ * A timeout is a host observation, not a CLI outcome, so the report carries
+ * what a diagnosis needs from the host: the machine's load — these deadlines
+ * expire under contention, not by the child's own doing — and whatever each
+ * channel received before the run was abandoned.
+ */
+function abandonedReport(args: string[], limit: number, partial: PartialOutput): string {
+  const load = loadavg()
+    .map((average) => average.toFixed(1))
+    .join(", ");
+  return [
+    `xmd ${args.join(" ")} timed out after ${limit}ms (load average ${load})`,
+    channel("stdout", partial.stdout),
+    channel("stderr", partial.stderr),
+  ].join("\n");
+}
+
+function channel(name: string, content: string): string {
+  return content.length === 0
+    ? `--- ${name} before the deadline: nothing ---`
+    : `--- ${name} before the deadline ---\n${content}`;
+}
+
 function cliEnv(options: CliRunOptions): Record<string, string> {
   const env: Record<string, string> = {};
   const names = options.inheritEnv ? Object.keys(process.env) : INHERITED;