feat(snippets): Snippet Revision Management API #190

[Olayiwola2904]

Overview

This PR implements the Snippet Revision Management API so every meaningful snippet update is stored as an immutable, sequentially numbered revision. Restoring a past revision never erases history — it appends a new revision with the restored content.

Related Issue

Changes

Revision Engine

• [ADD] lib/snippet-revisions.ts

  • createRevision — appends a new revision with sequential versionNumber
  • listRevisions — metadata list (version, timestamp, editor, preview)
  • compareRevisions — side-by-side diff via existing buildSideBySideDiff
  • restoreRevision — rolls back by creating a new revision entry
  • In-memory store + optional Neon snippet_revisions table
  • Audit trail for create / compare / restore / list (logEvent + in-memory)

• [ADD] lib/snippet-revisions.test.ts

  • Covers all acceptance criteria (create-on-update, list metadata, diff, restore-preserves-history, sequential versions, audit logging)

API Routes

• [ADD] POST/GET /api/snippets/:id/revisions
• [ADD] GET /api/snippets/:id/revisions/:revId/compare/:revId2
• [ADD] POST /api/snippets/:id/revisions/:revId/restore

Schema

• [ADD] docs/snippet-revisions-schema.sql — snippet_revisions table matching the issue example

Verification Results

Acceptance Criteria
✅ Every update creates a revision entry — no silent overwrites
✅ Revisions retrievable by snippet ID — version number, timestamp, editor
✅ Diff comparison works correctly — highlighted line diffs + stats
✅ Restore action creates a new revision — history preserved
✅ Version numbers increment sequentially — no duplicates or gaps
✅ Audit logging — create, compare, restore tracked

Acceptance Criteria	Status
Every update creates a revision entry	✅
Revisions retrievable by snippet ID	✅
Diff comparison works correctly	✅
Restore creates a new revision	✅
Version numbers increment sequentially	✅
Audit logging	✅

Closes #190

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