✅ Enforce 80% diff coverage

[Vivekyy]

Enforces an 80% diff line-coverage threshold in npm test using c8-generated LCOV and diff-cover against origin/main.
Coverage includes authored bin, src, and skill scripts while excluding generated output and tests, and reports uncovered changed lines.
CI now fetches full Git history so the comparison is available.
Validation: npm run typecheck, npm test, and npm run build.

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Greptile Summary

This PR adds diff-coverage enforcement to the test lifecycle.

• Instruments authored TypeScript and skill scripts with c8 and emits LCOV.
• Requires at least 80% coverage of changed lines through diff-cover.
• Fetches full Git history in the test workflow and adds the required development dependencies.

Confidence Score: 4/5

The Git-ref dependency in the standard test and publication lifecycle should be addressed before merging.

The new test command fails after otherwise successful tests whenever the checkout does not expose an origin/main ref, and the same command is invoked during package publication.

Files Needing Attention: package.json

Important Files Changed

Filename	Overview
package.json	Adds c8 configuration and an 80% diff-coverage gate, but makes the standard test lifecycle depend unconditionally on the origin/main Git ref.
.github/workflows/test.yml	Changes checkout to fetch full history so CI can perform the Git comparison.
package-lock.json	Locks the new c8 and diff-cover development dependency trees.

_{Reviews (1): Last reviewed commit: "✅ Enforce 80% diff coverage" | Re-trigger Greptile}

Greptile also left 1 inline comment on this PR.

[ghost]

Ready to review this PR? Stage has broken it down into 4 individual chapters for you:

	Title
1	Configure coverage tools and scripts
2	Enable full history for Git comparison
3	Integrate coverage enforcement into CI workflows
4	Other changes

_{Chapters generated by Stage for commit 8acaff3 on Jul 30, 2026 3:26pm UTC.}

[github-actions]

📦 No plugin release on merge

The plugin package, tag, and GitHub Release already exist for 0.1.3.
Bump package.json to release a new plugin version.

[greptile-apps]

Test command requires origin/main

When npm test runs from a checkout without an origin/main ref, the unconditional diff-cover comparison cannot resolve its default base branch, causing otherwise successful tests and coverage collection to exit unsuccessfully; prepublishOnly inherits the same Git-remote requirement.