[sdk-sentinel-bot]

Caution

This PR contains untrusted AI-generated code. Do not approve or run CI until a maintainer has reviewed the diff. SDK Sentinel verified that GitHub Actions remained approval-gated with zero executable jobs when this PR was opened.

Summary

• CI evidence: failed CI job · workflow run · last known pass · first known failure

Prevent the external-workflow cancellation test from racing its target timer. The failure appeared in the [macOS ARM time-skipping V2 job](https://github.com/temporalio/sdk-python/actions/runs/40522868526/job/122254383729). The [preceding main CI](https://github.com/temporalio/sdk-python/actions/runs/40519296785) passed, while the [first captured bad CI](https://github.com/temporalio/sdk-python/actions/runs/40522868526) failed with unchanged relevant code.

Root cause

The target used a 1000-second workflow timer. Time-skipping V2 can advance that timer before the separate cancellation workflow sends its request, letting the target complete normally instead of raising cancellation.

Fix

Use the existing timer-free wait-forever workflow as the target. External cancellation is now its only completion path, removing the nondeterministic ordering.

Validation

The failure did not reproduce in 50 pre-change stress iterations. With the fix, 100 time-skipping V2 iterations and one normal-environment run passed. The fixed repository validator and unchanged baseline passed. macOS ARM CI remains required.

Validation status: validated-without-reproduction

• Flake confidence: high
• Fix confidence: high
• Value: medium
• Patch scope: standard — 1 changed file; 1.4 KiB
• Local reproduction: not-reproduced — Fifty pre-change Linux time-skipping V2 stress iterations passed; the captured scheduling race did not occur locally.
• Regression coverage: pass-after-only — The existing focused test passed 100 time-skipping V2 stress iterations and one normal-environment iteration after the candidate.
• Unchanged baseline (Poe lint, bridge lint, and editable build) — passed
• Independent candidate (Poe lint, bridge lint, and editable build) — passed

Investigator-run checks

• poe test -s --workflow-environment time-skipping-v2 tests/worker/test_workflow.py::test_workflow_cancel_external --flake-finder --flake-runs 50 — passed; 50 attempt(s). Before the edit, all 50 iterations passed, so natural local reproduction was not obtained.
• poe test -s --workflow-environment time-skipping-v2 tests/worker/test_workflow.py::test_workflow_cancel_external --flake-finder --flake-runs 100 — passed; 100 attempt(s). All 100 iterations passed with the final candidate on Linux.
• poe test -s --workflow-environment local tests/worker/test_workflow.py::test_workflow_cancel_external — passed; 1 attempt(s). The timer-free target preserved normal local-environment cancellation behavior.
• .ci-flake-runtime/input/validate.sh — passed; 1 attempt(s). The fixed validator passed formatting, imports, type checks, docstyle, Rust clippy, and editable bridge build. The trusted unchanged baseline also passed.

Required target CI

• Continuous Integration / build-lint-test (3.10, macos-arm), time-skipping-v2 step

Residual risks

• The natural failure was not reproduced locally.
• The captured failure originated on macOS ARM, while local validation used Linux.

Automation provenance

• Investigator workflow
• Base SHA: 64b700540a14591f7bfcfebeaad2dfc5ba9cce1b

If this finding should not be fixed, apply the sdk-sentinel:false-positive label and close the PR. Sentinel will suppress the finding until its affected source changes.

SDK Sentinel recurrence history

• Unique failed CI run attempts: 1
• First occurrence: 2026-10-27 14:55 UTC
• Latest occurrence: 2026-10-27 14:55 UTC
• Recent occurrences:
  • 2026-10-27 14:55 UTC — failed CI job