perf: optimize step boundary cancellation check

[coji]

Summary

• Check controller.signal.aborted (in-memory) before storage.getRun() (DB query) at step boundaries
• When cancellation is detected via the run:cancel event, the DB query is skipped entirely
• Also adds signal check before replaying cached steps during resume, improving cancellation responsiveness for jobs with many completed steps
• DB fallback is preserved for edge cases (e.g., run cancelled while worker was down)

Changes

• packages/durably/src/context.ts: Add fast-path signal checks before DB queries

Test plan

• pnpm --filter durably test:node passes (186 tests)
• Existing cancellation tests cover both signal-based and DB-based cancellation paths

Fixes #38

🤖 Generated with Claude Code

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Project	Deployment	Actions	Updated (UTC)
durably-demo	Ready	Preview	Mar 4, 2026 2:51pm

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⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 547d5cd6-b4f6-4b1c-b317-6758184c7edf

📥 Commits

Reviewing files that changed from the base of the PR and between ac817a9 and f9772bb.

📒 Files selected for processing (1)

• packages/durably/src/context.ts

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch perf/step-boundary-cancel-check

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