CI: select the PostgreSQL, SQL Server, consumer and pack lanes from a derived map #112

Problem

Every PR runs every lane. Of the 42 merged PRs since 2026-06-02, 14 changed only docs or tests and still ran Integration, Consumer and Pack: 53 of 245 runner-minutes (22%), and about 1 minute of a 2.2-minute median wall-clock run. That alone is not worth it, because the minutes are free for a public repository.

#100 changes the balance. A SQL Server 2022 container lane on every PostgreSQL-only, docs or test-only PR costs every author its start-up and run time, and #101 adds work to the PostgreSQL lane.

Change

• A Scope job outputs true or false per lane: postgres, sqlserver, consumer, pack.
  • On any event other than pull_request, it selects every lane.
  • On a PR, it takes git diff --name-only --no-renames against the merge base and matches each path against .github/ci-lanes.json. The first match decides: a global file (Directory.Build.props, *.csproj, *.slnx, .github/workflows/**, the selector and map) selects every lane; a claimed path selects its lanes; an inert path (docs/**, *.md) selects nothing extra; anything else selects every lane.
  • Any error exits non-zero, and the gate (CI: one gate job as the only required build check #110) then fails.
• A convention test derives the map from MSBuild, so it is never hand-kept. Each lane gets its test projects' ProjectReference closure, project directories, linked items and imported props, and the test checks that every lane has a job whose if: reads it. While one test project holds both suites, any change under test/ selects both container lanes. The SQL Server suite must be its own project (Tests: a SQL Server integration lane that applies migrations to a live server #100) for the map to tell the lanes apart.
• Pack needs Test and Integration, so it gets an explicit !cancelled() condition. Otherwise it is skipped whenever a lane it needs is skipped, and the skip counts as passing.
• Push, release (Release: run the full CI before publishing, and a nightly full run #111), nightly and dispatch always run every lane. The push run replays the merged PR's selection and reports a selection escape if a lane fails that the PR would have skipped.

Done when

The SQL Server lane is skipped on a PostgreSQL-only PR and runs on a core or SqlServer change. Each of these seeds fails CI: a file renamed out of src/, a failing Scope, a misspelled lane output, and Pack skipped behind an unselected lane.