Prepare reproducible marketplace release candidates #248

🤖 Generated by the Agentic Engineer

Problem

The marketplace has no repository release tags. Its two marketplace manifests carry a version, but maintainers cannot yet turn a reviewed source revision into a consistent, reviewable release proposal. Per-plugin cache versions already have a separate lifecycle and must remain independent.

Proposed increment

Add an opt-in, offline release-preparation command. Given a source revision and either the last stable marketplace tag or an explicit first-release choice, it calculates the stable version from Conventional Commit history, prepares matching marketplace manifests, and emits revision-bound JSON and readable notes in a new output directory. It never publishes, pushes, modifies the checkout, or changes per-plugin versions. Add a manually dispatched read-only workflow for the same candidate artifact and an ADR explaining the preparation/publication boundary.

Acceptance criteria

• Real Git-history tests cover first release, patch/minor/major, scoped and breaking-footer changes, no-release histories, malformed or ambiguous inputs, and stale/unrelated baselines.
• Both source manifests and tagged-baseline metadata are validated before output; per-plugin content/version data is preserved.
• Complete source history and immutable commit identities are required; partial failures do not leave an apparently complete output directory.
• The candidate names the source and baseline commits, selected version, contributing commits, plugin inventory, and the fact that it grants no publication authority.
• Local use and a manual workflow produce the same artifact with read-only repository permissions. CI runs the offline regression suite.
• Exercise the tool on the real repository and document the remaining live tag-reservation/publication work under feat(ci): cut semver releases so the marketplace has a version to pin #101.

Size: M. Part of #101. Actual tag creation, GitHub release publication, and consumer rollout remain a separate increment.