[Breaking] Artifact-based rewrite

[pavi2410]

Summary

This PR is the full v4 -> v5 rewrite of html-preview-action.

The branch started by modernizing the action implementation and test setup, then moved the action to a new artifact-first architecture, and finally simplified the public API around the v5 direction: previewing HTML generated during CI as GitHub Actions artifacts.

Compared to v4, v5 is a breaking release with a narrower, clearer scope.

v4 -> v5 highlights

What v4 was designed for

v4 was built around previewing checked-in repository files by constructing an htmlpreview.github.io URL that points at a GitHub blob URL.

That only works for content that htmlpreview.github.io can read publicly from GitHub, which made it a reasonable fit for checked-in repo files but not for CI-generated preview payloads or private artifact-like output.

What v5 is designed for

v5 is intentionally focused on the most common and best-supported use case this project wants to support going forward:

• HTML generated during CI
• preview payloads uploaded as GitHub Actions artifacts
• linked local HTML/assets discovered automatically under site_root

The new implementation:

• resolves html_file within site_root
• recursively discovers linked local HTML pages and assets
• ignores remote, unsafe, missing, and out-of-root references
• uploads a single-file payload as raw when possible
• falls back to archive upload for multi-file previews

Runtime and tooling modernization

• upgraded the action runtime from Node 20 to Node 24
• migrated the implementation from legacy JavaScript entrypoints to TypeScript source under src/
• switched the packaged action bundle to dist/index.mjs
• added tsconfig.json and tsdown bundling
• moved the repo to pnpm
• replaced the old generated bundle/layout with the new ESM build output

Public API changes

The final v5 API is simpler and more explicit:

• removed mode
• removed artifact_format
• added upload with supported values:
  • auto
  • archive
• renamed input artifact_name to archive_name
• kept the action artifact-only

Output changes

Kept common outputs:

• url
• artifact_url
• artifact_id
• artifact_name
• discovered_files_count
• skipped_references_count
• comment_body

Added:

• result_json

Removed older / more confusing outputs:

• mode
• upload_strategy
• artifact_count
• artifact_names
• artifact_ids
• artifact_urls
• artifact_manifest
• source_url

Documentation updates

The README was rewritten for v5 to explain:

• the artifact-only model
• how discovery works behind the scenes
• how upload behavior is resolved
• when this action is a good fit
• when this action is not a good fit
• how to compose PR comments yourself
• how to migrate from v4 repo-mode usage

The migration section now includes:

• a direct pointer from the top-level breaking-change note
• a copy-pasteable workflow step that recreates the old repo/blob preview URL pattern for users who still need that behavior

Test and workflow changes

This PR also substantially upgrades verification coverage:

• added TypeScript unit tests around discovery, path safety, upload strategy, metadata, and helper behavior
• added richer test fixtures for:
  • single-file previews
  • linked multi-file previews
  • path escape attempts
• reworked .github/workflows/test.yml to run quality checks first
• updated action-invocation workflow coverage for the new artifact-only API
• added a dedicated v4_compatibility workflow job that validates the documented repo/blob fallback URL construction

Repository cleanup

• removed old IDE project files from the repo
• removed obsolete root-level sample/test files that no longer fit the new structure
• updated .gitignore
• removed the old package-lock.json
• added pnpm-lock.yaml

Why this change

The old design was centered on checked-in repo files that could be fetched publicly through htmlpreview.github.io.

v5 makes the action more explicit and maintainable by focusing on CI-generated HTML preview artifacts, while still giving former v4 users a documented fallback path when they still want the old checked-in-file behavior.

Verification

Verified with:

• pnpm format:check
• pnpm test
• pnpm typecheck
• pnpm lint
• pnpm build

Migration notes

For users upgrading from v4:

• v5 no longer supports repo/blob mode inside the action itself
• if you still need the old checked-in-file behavior, either stay on v4 or use the documented workflow fallback that constructs:

https://htmlpreview.github.io/?https://github.com/<owner>/<repo>/blob/<sha>/<html_file>