fix(core,github-action): stabilize version computation and PR creation

[rickmartensnl]

What has changed?

• sampo-core: Added run_stabilize_release, a new public function that transitions prerelease packages to stable. It uses a new private stabilize_version_from_parsed helper that strips the prerelease suffix and only applies an additional bump when the changeset requests a larger change than what the prerelease base already encodes (e.g. 0.2.7-alpha.6 + patch → 0.2.7, not 0.2.8). Added stabilize: bool to compute_plan_state and prepare_release_plan to route version computation through this helper.
• sampo-github-action: prepare_stabilize_pr no longer calls exit_prerelease before computing the release plan. It now uses capture_stabilize_plan and run_stabilize_release, which compute the correct stable version in one step. execute_operations (Auto mode) now checks for prerelease packages when capture_release_plan returns no changes, so a stabilize PR is created even after a prerelease PR has been merged and its changesets moved to .sampo/prerelease/.

How is it tested?

• Added test_stabilize_version_from_parsed unit test in release.rs covering patch/minor/major bumps against patch-, minor-, and major-implied prereleases, plus stable inputs.
• Added 7 integration tests in release_tests.rs: current-changeset scenarios (Bug 1) and preserved-changeset scenarios (Bug 2), including a dry-run variant.

How is it documented?

No documentation changes needed — these are internal fixes with no user-facing API or configuration changes.

[sampo-s-bot]

🧭 Changeset detected

Merging this PR will release the following updates:

sampo-core (Cargo) — patch version bump

Patch changes

• Fixed incorrect stable version computation when stabilizing a prerelease package (e.g. 0.2.7-alpha.6 + patch now correctly produces 0.2.7 instead of 0.2.8), and fixed the stabilize PR not being created after merging a prerelease PR when all preserved changesets target packages still in prerelease.

sampo-github-action (Cargo) — patch version bump

Patch changes

• Fixed incorrect stable version computation when stabilizing a prerelease package (e.g. 0.2.7-alpha.6 + patch now correctly produces 0.2.7 instead of 0.2.8), and fixed the stabilize PR not being created after merging a prerelease PR when all preserved changesets target packages still in prerelease.

[Copilot]

Pull request overview

This PR stabilizes how stable version numbers are computed when transitioning prerelease crates to stable, and updates the GitHub Action flow so a stabilize PR can still be created when changesets were preserved under .sampo/prerelease/.

Changes:

• Add run_stabilize_release to sampo-core, including stabilize_version_from_parsed to correctly strip prerelease suffixes without over-bumping.
• Update sampo-github-action to compute and execute stabilization via the new core API (without calling exit_prerelease first), and to detect prerelease packages even when the normal changesets dir has no pending entries.
• Add unit + integration tests covering stabilize scenarios (including preserved-changeset and dry-run cases).

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
crates/sampo-github-action/src/sampo.rs	Adds action-layer wrappers to dry-run capture and execute stabilize releases via sampo-core.
crates/sampo-github-action/src/main.rs	Ensures Auto mode can still prepare a stabilize PR when prerelease packages exist but the normal changesets dir is empty; switches stabilize PR flow to new stabilize plan/release functions.
crates/sampo-core/src/release.rs	Implements run_stabilize_release, threads a stabilize flag into planning, and adds stabilize_version_from_parsed.
crates/sampo-core/src/release_tests.rs	Adds integration tests for stabilize behavior across current/preserved changesets and dry-run.
crates/sampo-core/src/lib.rs	Re-exports run_stabilize_release.
.sampo/changesets/virtuous-lord-vellamo.md	Records the fix as a patch changeset for core + action crates.

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[Copilot]

After removing the exit_prerelease call, prepare_stabilize_pr still collects prerelease_packages but no longer uses it, which will produce an unused-variable warning (and can break builds if warnings are denied). Remove the binding, prefix it with _, or use it (e.g., for logging).