[copilot-finds] Bug: Retry handler returning undefined/null/NaN/Infinity causes infinite retry loop or invalid timer

[github-actions]

Problem

In packages/durabletask-js/src/worker/orchestration-executor.ts, the tryHandleRetry method uses a negative check (retryResult !== false) to determine whether a custom retry handler wants to retry a failed task. This means any value that is not strictly false — including undefined, null, NaN, and Infinity — is treated as "retry".

This causes two distinct failure modes:

1. Infinite retry loop: If a retry handler has a code path that returns undefined (common JavaScript mistake — a missing return statement in a branch), the task is rescheduled immediately and retries forever, without any delay.

2. Invalid timer creation: If the handler returns NaN or Infinity, these pass the typeof === "number" check but create timers with invalid fire-at dates, causing unpredictable behavior.

Affected code (line ~795):

if (retryResult !== false) {  // BUG: undefined, null, NaN, Infinity all pass this check

Example — handler with missing return:

const retryHandler = async (ctx) => {
  if (ctx.lastAttemptNumber >= 5) {
    return false;
  }
  // Oops — forgot "return true" here, returns undefined
};

This handler intends to stop retrying after 5 attempts, but on attempts 1–4 it returns undefined, which the SDK treats as "retry immediately" — creating an infinite loop until the 5th attempt.

While TypeScript types (RetryHandlerResult = boolean | number) catch this at compile time, JavaScript consumers and as any casts bypass this protection. The SDK should defensively handle unexpected return values at runtime.

Root Cause

The condition retryResult !== false is a negative check that accepts ANY value except false. The correct pattern is a positive check: only accept values that are explicitly true or a finite number.

Proposed Fix

Change the condition to a positive check:

if (retryResult === true || (typeof retryResult === "number" && Number.isFinite(retryResult)))

This ensures:

• true → retry immediately ✓
• false → stop retrying ✓
• Finite positive number → retry with delay ✓
• Finite zero/negative number → retry immediately ✓ (preserves existing behavior)
• undefined, null → stop retrying ✓ (FIXED)
• NaN, Infinity → stop retrying ✓ (FIXED)

Impact

• Severity: High — can cause infinite retry loops, resource exhaustion, and orchestration hangs
• Affected scenarios: Any orchestration using AsyncRetryHandler or RetryHandler where the handler has a code path that does not explicitly return true, false, or a number
• Likelihood: Medium — most common in JavaScript consumers or TypeScript code with partial branch coverage

[github-actions]

Fix Ready

Branch copilot-finds/bug/fix-retry-handler-undefined-return-infinite-loop contains the fix.

Note: The GitHub Actions workflow token doesn't have permission to create pull requests in this repository. Please create a PR manually from this branch.

Changes

• orchestration-executor.ts: Changed retryResult !== false to retryResult === true || (typeof retryResult === 'number' && Number.isFinite(retryResult)) — prevents infinite retry on undefined/null and invalid timers on NaN/Infinity
• orchestration_executor.spec.ts: Added 6 new unit tests covering undefined, null, positive delay, zero delay, NaN, and Infinity return values

All 754 existing tests + 6 new tests pass. Lint clean.