The fix wasn't more compute: how we cut merge-queue CI time in half

A team reduced merge-queue integration test times by replacing a single shared test account with isolated per-worker identities and splitting five unusually long test files, rather than purchasing larger CI runners or simply increasing parallelism. The serial live-backend suite had grown from a 4.4-minute median in February to 10.1 minutes in June, with a 23-minute p90 and occasional runs exceeding 30 minutes, creating substantial queue delays. Because shared account state, API keys, resources, and rate limits made parallel execution unsafe, the team first created a pool of test users matched to Vitest worker count, then divided 123 tests from five large files into 22 self-contained files to remove long-running bottlenecks. Repeated non-gating canary runs distinguished infrastructure-related network failures from a genuine concurrency issue in an adversarial rate-limit test, which was excluded from the pooled lane without weakening its coverage. After production rollout on June 24, 2026, median merge-queue runtime fell to 4.5 minutes across the first 19 runs, roughly a 55 percent reduction, while all pooled runs remained below nine minutes; the remaining constraint is primarily network latency in the tests themselves rather than worker capacity.

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