Give ReleaseCommand an end-to-end test harness

[rdeago]

Reference version

2.1.70-preview (latest published version); analysis done at commit bcb836c, where the merged line coverage of ReleaseCommand is 0/154.

Background and motivation

Issue #320 extracted the extractable logic from ReleaseCommand (hook-args assembly into PostReleaseHookArgsFactory, working-tree change tracking into GitService.TrackChangesAsync), but what remains is exactly what cannot move out: sequencing and policy. The release commit must exist before the artifact pass; the tag check must precede pack; the post-release commit assembles hook changes and dogfood rewrites; push precedes NuGet push. A regression in that ordering surfaces only during an actual release — still the worst possible moment, since releases are not rehearsable locally. And every PR that touches ReleaseCommand accrues a few uncovered patch lines that Codecov rightly flags, with no way to do better until the orchestrator is executable under test.

Proposed enhancement

ReleaseCommand.ExecuteAsync runs end-to-end in a test harness, with only the process and platform boundaries faked, so the sequencing itself is covered by tests.

Implementation proposals

• Drive the real services over a TempGitRepo with a VERSION file and a buildvana.json: real GitService, VersionService, ChangelogService, HookRunner. The composition stays honest — no mock-and-assert-the-mock.
• Fake only the boundaries that already have seams: IProcessRunner (FakeProcessRunner exists in Buildvana.Core.Testing) for dotnet invocations, IFileBasedAppRunner for hooks, and a test ServerAdapter (the class is already abstract with a factory) whose release object records UpdateRepository / AddPostReleaseCommit / AddAsset / PushUpdates / PublishAsync calls in order.
• Assert observable sequences: happy-path prerelease release; changelog policy variants (none | stable | all, empty-section substitute); hook-modified files joining the post-release commit; version-spec change application; tag-collision failure.
• The test ServerAdapter must not deepen the current adapter shape: the platform/git-host split is planned, so the fake should be designed against the seams that split will keep.

Usage examples

Not user-facing; example of the kind of test this enables:

[Test]
public async Task Release_AssemblesPostReleaseCommit_FromHookChangesAndDogfoodRewrites() { /* ... */ }

Risks

The harness may reveal that some services need construction seams (e.g. BuildPipeline); prefer constructor-level composition over new interfaces. Test-only change; no changelog entry unless behavior fixes fall out.

Additional information

Follow-up to #320, which deliberately stopped at extraction; the residue this issue covers is the part extraction cannot reach.