Bug: error in finally during halt propagates despite being caught

[taras]

Motivation

When a child task throws in a finally block during halt, the error propagates through two independent paths:

1. Through halt() return — the caller's try/catch catches it ✓
2. Through the scope tree — fails the parent scope unconditionally ✗

This means even when the caller explicitly handles the error from yield* task.halt(), the parent scope is still considered failed and the error escapes.

let result = run(function* () {
  let task = yield* spawn(function* () {
    try {
      yield* suspend();
    } finally {
      throw new Error("finally-boom");
    }
  });

  yield* sleep(0);

  try {
    yield* task.halt();
  } catch (error) {
    // Error IS caught here ✓
  }

  return "success"; // This executes ✓
});

// But the run() rejects with "finally-boom" instead of resolving with "success" ✗
await expect(result).resolves.toEqual("success");

All three variants reproduce: synchronous throw, synchronous action reject, and async until(Promise.reject(...)).

Approach

This PR adds a single failing test to test/spawn.test.ts that demonstrates the bug. No fix is included — this is intended to document the issue and serve as a regression test for a future fix.

[pkg-pr-new]

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npm i https://pkg.pr.new/thefrontside/effection@1128

commit: 661ea3f