[copilot-finds] Bug: Sub-orchestration watcher in InMemoryOrchestrationBackend uses unintended 30s default timeout

[github-actions]

Problem

watchSubOrchestration in InMemoryOrchestrationBackend (packages/durabletask-js/src/testing/in-memory-backend.ts:592) intends to wait indefinitely for a sub-orchestration to complete, as explicitly documented by the inline comment:

// No timeout - sub-orchestration will eventually complete, fail, or be terminated

However, no timeoutMs argument is actually passed to waitForState, so the default 30-second timeout applies. After 30 seconds, the timeout error is silently swallowed by the .catch(() => {}) handler, and the completion/failure event is never delivered to the parent orchestration.

Root Cause

waitForState(instanceId, predicate) defaults timeoutMs to 30000. The comment in watchSubOrchestration says "No timeout" but no timeout argument is passed:

this.waitForState(
  subInstanceId,
  (inst) => this.isTerminalStatus(inst.status),
  // No timeout - sub-orchestration will eventually complete, fail, or be terminated
)

The comments are just inline annotations — they don't affect the function call, which silently uses the 30000ms default.

Proposed Fix

1. Modify waitForState to support no-timeout mode when timeoutMs is 0 (skip creating the setTimeout timer)
2. Pass 0 from watchSubOrchestration to match the documented intent
3. Add unit tests verifying sub-orchestrations with timer delays and failure propagation

Impact

Severity: Medium — affects the in-memory testing backend, not production gRPC communication.

Scenarios affected: Any test using the in-memory backend where a sub-orchestration takes more than 30 real seconds to complete (e.g., sub-orchestrations using timers, retry backoff, or waiting for external events). The parent orchestration hangs indefinitely because the sub-orchestration completion event is silently lost.

[github-actions]

Branch copilot-finds/bug/fix-sub-orchestration-watcher-timeout has been pushed with the fix and tests. A PR could not be created automatically due to GitHub Actions permissions.

Changes:

• packages/durabletask-js/src/testing/in-memory-backend.ts: Modified waitForState to support no-timeout mode (timeoutMs=0), and updated watchSubOrchestration to use it.
• packages/durabletask-js/test/in-memory-backend.spec.ts: Added 5 new tests — sub-orchestrations with timers, sub-orchestration failure, and waitForState zero-timeout behavior.

All 835 tests pass (771 + 64), lint is clean.