CI-07: Replace the duplicate full Windows PR matrix with a targeted Windows compatibility contract

[Chris0Jeky]

Wave: Smart CI Fabric (ADR-0066 §Decision 6). Tracker: CI-00 #2324. Lane: platform right-sizing.

Context

Windows currently runs as a second semantic platform: full backend unit, full API, full frontend (lint/type/build/coverage after the launcher regression), plus the worktree-helper harness. On a Pro private repo Windows minutes count 2x. Most Domain/Application/TypeScript semantics do not differ by OS; the things that do are launchers, PowerShell, paths/casing, process lifecycle and stdio, SQLite locking, desktop startup, MCP host, Job Object containment, packaging.

Scope

• Define the Windows compatibility contract: the exact test classes/specs that exercise platform-sensitive behaviour (.cmd/.ps1 launchers, dev-up pipeline, path semantics, process supervision, MCP stdio/HTTP host startup, SQLite concurrency, desktop bootstrap, worker containment, packaged-archive checks) — checked in as a lane in ci/test-ownership.v1.json.
• Ordinary PRs run only the contract on Windows unless the planner selects expanded coverage for platform-sensitive changes; the full Windows suite runs weekly and at release qualification until parity evidence (>=8 weeks without a Windows-only regression outside the contract) justifies a smaller matrix.
• Every historically Windows-only regression is represented in the contract or documented as covered elsewhere (search closed issues labelled ci + Windows; #2157, #2159, #2161 dev-up flakes belong here and to CI-15).
• Stated ordinary-PR Windows budget (target <=8 min wall).

Acceptance

• Contract lane merged and green; the mapping from historical Windows regressions to contract tests is recorded in docs/TESTING_GUIDE.md.
• Ordinary R0–R2 PRs stop running the full Windows backend/API/frontend suites only after the CI-02 recall report shows the contract would have caught every Windows-only failure in the window.
• Weekly full Windows sweep exists (CI-10) before the PR matrix shrinks.
• Planner selects expanded Windows coverage for desktop-windows, mcp-process, launchers, persistence groups.

Dependencies / release

Depends on CI-05 (ownership), CI-06 for the API shard split (may land in parallel with the full API union kept). Milestone v0.3.

[Chris0Jeky]

Sizing constraint from the 2026-09-03 SC-3 re-ruling (maintainer, on #2337). Hosted Actions spend only the included 3,000 minutes/month and only on Linux; Windows minutes count x2 and there is no overage budget. So the targeted Windows contract this issue defines must fit inside what the Linux-first allowance tolerates, and the "full Windows suite retained weekly/release during the evidence period" (checklist E) runs on the local laptop runner (CI-04 #2328) or as agent-run proving checks, not on windows-latest. Please size the hosted Windows leg accordingly and record the per-run Windows allowance cost in the CI-12 report.

[Chris0Jeky]

Correction to my note above, after review of PR #2462: the hosted budget is Linux only, so there is no "hosted Windows leg sized to the allowance" once the repository is private. Hosted Windows legs run only while the repository is still public and free; from cutover, Windows evidence is local only (laptop runner via CI-04 #2328 once registered, agent-run proving checks until then). Size the Windows contract for local execution. The checklist and ADR-0066 now say exactly this.

[Chris0Jeky]

Scoping note from the 2026-09-04 overnight run (read-only pass; no change made). Tonight the Windows launcher regression suite (scripts/ci/dev-up.test.mjs, step "Run source launcher regression suite" in the required Frontend Unit (windows-latest) job) produced two false reds on PRs that touch nothing near dev-up (#2506: "Vite fallback leaves the foreign frontend-port owner alive"; #2497: "pipeline cancellation runs transactional cleanup from finally"), after #2478 had already bounded the hang class. One root cause is now named (Wait-PortRelease's fixed 5 s / dual-stack bind in scripts/dev-up.ps1 vs hosted socket linger; fix PR in preparation under #1898).

Proposal for CI-07, consistent with the SC-3 re-ruling (hosted minutes are Linux-only; Windows evidence is local): add if: runner.os == 'Linux' to that step in reusable-frontend-unit.yml so the launcher suite stays on the Linux leg and on the local-runner path, and either drop the hosted Windows launcher run or keep it as a non-required advisory job (a continue-on-error job still burns 2x minutes).

This is a T2 control-plane change, so per ADR-0066's 2026-09-03 amendment it merges only after the maintainer's review. Queued in OUTSTANDING_TASKS.md §J for that decision rather than implemented unilaterally.