Problem

No git blame equivalent exists. There is no way to determine which commit last modified each line of a file.

Impact

• Code review UIs cannot show per-line attribution
• Cannot answer “who changed this line and when?”
• Common developer workflow unsupported

Acceptance Criteria

• blame(repo, ref, path) returns per-line attribution (commit SHA, author, date)
• Handles file renames (follow across renames, configurable)
• Handles merge commits correctly
• Performance: bounded memory for large files
• Output matches git blame --porcelain format for interop
• Tests covering: simple blame, merge blame, rename tracking