CI Speedup

Make the wait from push to green shorter, measured, and written down.

• IS: measuring a pipeline's critical path from run timestamps, choosing the levers that shorten it, changing workflow and test configuration, and recording before and after with the trend that says when the next round is due.
• IS NOT: getting a red build green (pr-babysitter), writing a pipeline for a package that has none (scaffold-cli), or general repository hygiene.

What Changes the Number

Wall-clock is the slowest chain of dependent jobs, not their sum. The number is push to green for one pull request, median and p90 over recent runs. Around five minutes an agent loop stops waiting on checks and the bottleneck moves to deploy and review. A lever that saves runner minutes off the critical path is a cost saving, and the ledger records it as one.

Three ratios decide what to do next:

• Setup tax. Checkout, runtime, dependencies, and service boot, per job. 110 seconds of setup around 60 of work is a batching candidate; around 400 it is a sharding candidate. Each shard adds a setup, so cut setup before adding shards.
• Import versus test. When Vitest's import plus environment figures exceed its tests figure, the suite pays to boot the module graph per file. A shared registry or a lighter environment moves that; more shards only spread it.
• Gate versus work. Change detection, matrix computation, and cache saves sit on the chain. Anything they do beyond deciding is paid by every job behind them.

Reference Files