test(runner): add direct tests for the capability live-process wait helper

The waitForCapabilityLiveProcess helper had no direct test. Add tests
for a first-attempt success, a retry after a thrown error, a deadline
failure that carries the last observed error as its cause, and a
deadline failure when the callback never settles. The tests use fake
timers, so they run in milliseconds instead of the real 10,000 ms
deadline.

Co-authored-by: Paperclip <noreply@paperclip.ing>

packages/paperclip-runner/src/live/wait-for-live-process.test.ts

@@ -0,0 +1,94 @@
+import { afterEach, describe, expect, it, vi } from "vitest";
+
+import {
+  CAPABILITY_LIVE_PROCESS_WAIT_DEADLINE_MS,
+  waitForCapabilityLiveProcess,
+} from "../../test/wait-for-live-process.js";
+
+afterEach(() => {
+  vi.useRealTimers();
+});
+
+describe("waitForCapabilityLiveProcess", () => {
+  it("returns the callback's value when the first attempt succeeds", async () => {
+    const result = await waitForCapabilityLiveProcess(
+      "first-attempt-succeeds",
+      () => "ok",
+    );
+
+    expect(result).toBe("ok");
+  });
+
+  it("retries a callback that throws, and returns the value when a later attempt succeeds", async () => {
+    vi.useFakeTimers();
+    let attempts = 0;
+    const promise = waitForCapabilityLiveProcess(
+      "retries-then-succeeds",
+      () => {
+        attempts += 1;
+        if (attempts === 1) throw new Error("first attempt failed");
+        return "recovered";
+      },
+    );
+
+    await vi.advanceTimersByTimeAsync(100);
+
+    await expect(promise).resolves.toBe("recovered");
+    expect(attempts).toBe(2);
+  });
+
+  it("fails at the deadline when every attempt throws, naming the label and the elapsed time and carrying the last observed error as its cause", async () => {
+    vi.useFakeTimers();
+    const lastError = new Error("connection refused");
+    const promise = waitForCapabilityLiveProcess("always-fails", () => {
+      throw lastError;
+    });
+    const caughtError = promise.catch((error: unknown) => error);
+
+    await vi.advanceTimersByTimeAsync(
+      CAPABILITY_LIVE_PROCESS_WAIT_DEADLINE_MS + 200,
+    );
+
+    const error = (await caughtError) as Error;
+    expect(error).toBeInstanceOf(Error);
+    expect(error.message).toContain("always-fails");
+    expect(error.message).toContain(
+      `did not settle within ${CAPABILITY_LIVE_PROCESS_WAIT_DEADLINE_MS}ms`,
+    );
+    expect(error.message).toMatch(/observed \d+ms/);
+    expect(error.message).toContain("connection refused");
+    expect(error.cause).toBe(lastError);
+  });
+
+  it("fails at the deadline, instead of running past it, when the callback never settles, and raises no unhandled rejection", async () => {
+    vi.useFakeTimers();
+    const unhandledRejections: unknown[] = [];
+    const onUnhandledRejection = (reason: unknown) => {
+      unhandledRejections.push(reason);
+    };
+    process.on("unhandledRejection", onUnhandledRejection);
+
+    try {
+      const promise = waitForCapabilityLiveProcess(
+        "never-settles",
+        () => new Promise<never>(() => {}),
+      );
+      const caughtError = promise.catch((error: unknown) => error);
+
+      await vi.advanceTimersByTimeAsync(
+        CAPABILITY_LIVE_PROCESS_WAIT_DEADLINE_MS + 200,
+      );
+
+      const error = (await caughtError) as Error;
+      expect(error).toBeInstanceOf(Error);
+      expect(error.message).toContain("never-settles");
+      expect(error.message).toContain(
+        `did not settle within ${CAPABILITY_LIVE_PROCESS_WAIT_DEADLINE_MS}ms`,
+      );
+    } finally {
+      process.off("unhandledRejection", onUnhandledRejection);
+    }
+
+    expect(unhandledRejections).toEqual([]);
+  });
+});