Linear rebuilt CI because AI-generated PRs saturated the runners, and published every change.

Third-party runners instead of GitHub Actions (34% faster jobs, 52% on TypeScript compilation), tsgo replacing tsc (73% off the typecheck median), change detection cut from 26s to 8s median via capped fetch depth and sparse blobless checkouts, a custom checkout action with retry and connection timeouts, pre-installed Postgres client in the base image (7-8s per test shard), pnpm workspace installs scoped to one package (44-73s down to 16-18s), seven checks consolidated into two jobs (~87,000 runner-minutes a month), four shards to eight, and an opt-in isolate: false Vitest project sharing module state for ~17% monthly savings. PR wait went from over 6 minutes to just over 5 while the suite nearly quadrupled. (Linear)