Problem

Only pre_receive_hook is implemented in receive-pack. There is no support for update (per-ref) or post-receive (after successful update) hooks. These are essential for triggering downstream actions.

Impact

• Cannot trigger CI pipelines on push
• Cannot send notifications on ref updates
• Cannot implement per-ref authorization (update hook)
• Limits usefulness as a git hosting server

Acceptance Criteria

• update hook: called per-ref with (ref, old_sha, new_sha), can reject individual refs
• post_receive hook: called after all refs updated, receives list of changes
• Hooks are pluggable functions (same pattern as existing pre_receive_hook)
• Hook failures in update reject only the affected ref, not the entire push
• post_receive failures are logged but don’t affect the push result
• Tests for each hook type including partial rejection scenarios