Feature Request: Support auto-generation of CHANGELOG.md when missing

[nyaomaru]

Summary

Currently, if no CHANGELOG.md exists, the Action fails at runtime with an error.
Instead, I propose that the Action should auto-generate a minimal changelog file when it is missing.
This would make the first-run and sandbox experience much smoother.

Current behavior

Running the Action in a fresh repository without a changelog results in:

Run nyaomaru/universal-version-bump@feature/jsr-version-bump-support
Detected platform: node
Bump targets: []
version: 0.1.0
/usr/bin/git describe --tags --abbrev=0
v0.0.0
/usr/bin/git log v0.0.0..HEAD --oneline
Error: File not found: Changelog file not found at CHANGELOG.md

Proposed solution

Introduce a simple option to control behavior when no changelog file exists:

• changelog_path (default: CHANGELOG.md)
• changelog_mode (default: auto)
  • auto: Create the changelog file if missing, then append new entries.
  • fail: Current strict behavior — throw an error if the file is missing.

This keeps the interface simple (two clear choices) while improving the first-run experience.

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I believe this change would make the Action friendlier for new users and sandbox testing, while still allowing strict mode for teams that prefer it. 🚀

Looking forward to hearing your thoughts on this proposal! 😻

[taj54]

Thanks for the suggestion @nyaomaru . Please proceed to open a PR.