fix(world-postgres): throw EntityConflictError on duplicate run_created

[joeyhotz]

Description

events.create with a run_created event inserts the run with onConflictDoNothing(), so when the run already exists the insert returns no row and create resolves with { run: undefined } instead of signalling the conflict. start() asserts on that field and throws Missing 'run' in server response for 'run_created' event — even though the run is healthy and already running.

This is the race start() documents: it fires events.create(run_created) and world.queue() in parallel, and when the worker dequeues first, run_started on the not-yet-existent run takes the resilient start path and creates the run itself. start() already treats EntityConflictError here as benign ("we can safely return", expected in <=1% of cases) — but the Postgres world never gives it one. world-local throws it for this same race and world-vercel surfaces a 409 that maps to it; world-postgres is the only world that resolves silently.

Throwing before the event insert also stops a duplicate run_created landing in the event log.

Observed on a self-hosted Postgres deployment on 3 of 261 runs (~1%, matching the estimate above) of our highest-frequency workflow over 7 days: each affected run has two run_created events and completed normally, while the trigger that started it returned a 500.

How did you test your changes?

Two cases added to packages/world-postgres/test/storage.test.ts (runs › create):

• rejects a duplicate run_created with EntityConflictError — the direct conflict.
• rejects run_created when resilient start already created the run — reproduces the production race (run_started on a non-existent run → resilient start → late run_created), asserting exactly one run_created remains in the event log.

Both resolve instead of rejecting against the current insert, and pass with the fix.

• pnpm --filter @workflow/world-postgres exec vitest run test/storage.test.ts (119 tests)
• pnpm --filter @workflow/world-postgres typecheck
• biome check packages/world-postgres/src/storage.ts packages/world-postgres/test/storage.test.ts

PR Checklist - Required to merge

• 📦 pnpm changeset was run to create a changelog for this PR
• 🔒 DCO sign-off passes (run git commit --signoff on your commits)
• 📝 Ping @vercel/workflow in a comment once the PR is ready, and the above checklist is complete

[changeset-bot]

🦋 Changeset detected

Latest commit: 9e0319e

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@workflow/world-postgres	Patch

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[joeyhotz]

Pinging @vercel/workflow

[github-actions]

Backport PR opened against stable: #2992. Merge conflicts were resolved by AI — please review carefully. (backport job run)