fix: validate plugin input early before git operations [ED-25747]

[davseve]

Summary

Addresses @Ntnelbaba's code review comment on PR #60: "And if the value is 'koko'?"

This PR makes invalid plugin input values (like "koko") fail fast with a clear error message before any git branch operations occur, preventing wasted work and avoiding branch checkout mutations.

Background

PR #60 added a new plugin input (core or pro) to the release-tag-creation composite action. The validation logic resolvePluginConfig(plugin) in plugin-config.ts already throws plugin must be "core" or "pro", got "<x>" for invalid values, but that validation only ran inside the "Update version files" step (step 5), which is AFTER:

1. Install dependencies
2. Handle version input
3. Switch to release branch (git checkout) ← branch mutated
4. Config git user

So an invalid plugin value like "koko" would waste work and mutate the working tree before failing.

What Changed

• Early validation: main.ts now imports and calls resolvePluginConfig(plugin) at the very start of the run() function, before any version format checks or git operations.
• New helper: Added getPlugin() to read INPUT_PLUGIN env var (defaults to "core").
• Action YAML: Added INPUT_PLUGIN: ${{ inputs.plugin }} to the "Handle version input" step so the plugin value is available.
• Tests:
  • Created main.test.ts with unit tests for the plugin validation behavior.
  • Extended plugin-config.test.ts to explicitly include the "koko" test case mentioned in the review.

How It Works

The "Handle version input" step now:

1. ✅ Validates plugin (resolvePluginConfig(plugin))
2. ✅ Validates version format
3. ✅ Checks tag doesn't exist
4. ✅ Derives channel and branch

Only after all input validations pass does the workflow proceed to git checkout of the release branch.

Testing

• ✅ vitest passes (49 tests including new plugin validation tests)
• ✅ tsc type-checking passes
• ✅ eslint passes

Related

• Closes issue raised in PR #60 review comment
• Jira: ED-25747

  

[Ntnelbaba]

Low: getPlugin() trims, but update-version-files.ts reads INPUT_PLUGIN via getEnv() without trimming. A value like " pro " passes this early check and then fails in 'Update version files' (after the release-branch checkout), which is the late failure this PR is meant to prevent. Either drop .trim() here so both steps reject it at step 2, or trim in update-version-files.ts as well.

[Ntnelbaba]

Low: this file never imports main.ts; it only re-tests resolvePluginConfig, which plugin-config.test.ts already covers (koko is now in both). getPlugin()'s default/trim and the 'plugin is validated before git ls-remote' order in run() are untested. Because main.ts ends with a bare run();, consider the same split as #60 (run-main.ts entrypoint), then test run() with INPUT_PLUGIN=koko and assert process.exit(1) and that spawnSync was never called.