Make ReleaseCommand's post-release hook-context assembly unit-testable

[rdeago]

Reference version

2.1.19-preview (gap highlighted by the Codecov report on PR #319)

Background and motivation

Since #319, PostReleaseHookContext is the typed contract between bv and repo-owned post-release hooks. ReleaseCommand assembles it inline (ReleaseCommand.cs#L243-L266): well-known paths (with Path.GetFullPath anchoring for the artifacts and scratch directories), release/version fields, produced packages, and the dogfooding flag — plus the working-tree snapshot diff that detects which files the hook modified.

None of this is unit-tested: ReleaseCommand is a large orchestrator that resolves a dozen services and only runs on cloud builds, so it has no test harness at all. Codecov flags the 14 new context-assembly lines at 0% patch coverage. A mistake in path anchoring, a mixed-up version field (Version vs SemVer), or a regression in the dirty-files diffing would only surface during an actual release — the worst possible moment, since releases are not rehearsable locally.

Proposed enhancement

The hook-context assembly and the hook-change detection logic are covered by unit tests. bv's observable behavior does not change.

Implementation proposals

• Extract the context assembly from ReleaseCommand into a small internal factory (e.g., PostReleaseHookContextFactory in Buildvana.Tool/Services/Hooks/) taking the home directory provider, artifacts path, version information, produced packages, and dogfood flag. ReleaseCommand delegates to it.
• Move the "snapshot dirty files around the hook run" logic next to HookRunner (e.g., a helper that runs a hook and returns the set of files it modified), so it can be tested with the fakes already used by HookRunnerTests.
• Add tests in Buildvana.Tool.Tests alongside HookRunnerTests and PostReleaseHookContextTests: path anchoring (relative artifacts path → absolute), version field mapping including PreviousVersion = null for a first release, and modified-file detection (no changes / changes / hook absent).

Usage examples

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

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

Risks

Refactor-only; no public surface or behavior change, so no changelog entry needed. Main risk is cosmetic churn in ReleaseCommand; the extraction is mechanical.

Additional information

Flagged as a non-blocking note in the PR #319 review; acknowledged as a pre-existing gap in this reply.