feat: add breadcrumb detection for Cursor via hooks

[sehajc]

Summary

• Enables aittributor to detect Cursor via tier 4 (breadcrumb) detection, complementing existing process-based detection (tiers 1-3).
• Sets breadcrumb_dir to ~/.cursor/attribution and breadcrumb_ext to jsonl on the Cursor agent definition.
• Adds a test validating the Cursor breadcrumb format works with the existing find_session_file_with_cwd pipeline.

Motivation

Cursor is currently detected only via process scanning. If a developer uses Cursor to generate code, closes the editor, and commits later from a terminal, aittributor misses the attribution. This is the same gap that breadcrumbs solve for Claude (~/.claude/projects/) and Codex (~/.codex/sessions/).

How it works

A Cursor afterFileEdit hook (configured in ~/.cursor/hooks.json) writes a breadcrumb file to ~/.cursor/attribution/<repo-slug>.jsonl containing {"cwd":"<repo-root>"} every time the AI edits a file. The format is intentionally compatible with aittributor's existing extract_cwd_from_json parser — no changes to the detection pipeline are needed.

At commit time, aittributor's tier 4 breadcrumb check walks ~/.cursor/attribution/, finds recent .jsonl files (mtime < 2h), and matches the cwd field against the current repo. If matched, Co-authored-by: Cursor <cursoragent@cursor.com> is appended.

Cursor hook setup (user-level, ~/.cursor/hooks.json)

{
  "version": 1,
  "hooks": {
    "afterFileEdit": [
      { "command": "./hooks/write-attribution-breadcrumb.sh" }
    ]
  }
}

Breadcrumb writer (~/.cursor/hooks/write-attribution-breadcrumb.sh)

#!/bin/bash
input=$(cat)
file_path=$(echo "$input" | jq -r '.file_path // empty')
[ -z "$file_path" ] && exit 0
repo_root=$(cd "$(dirname "$file_path")" 2>/dev/null && git rev-parse --show-toplevel 2>/dev/null)
[ -z "$repo_root" ] && exit 0
breadcrumb_dir="$HOME/.cursor/attribution"
mkdir -p "$breadcrumb_dir"
repo_slug=$(echo "$repo_root" | tr '/' '_')
echo "{\"cwd\":\"$repo_root\"}" >"$breadcrumb_dir/${repo_slug}.jsonl"
exit 0

Distribution

The hook files can be distributed to engineers via:

• Dotfile managers (e.g., symlink hooks.json and the script into ~/.cursor/ as part of your org's shared dotfiles)
• Cursor enterprise hooks (/Library/Application Support/Cursor/hooks.json on macOS, deployed via MDM)
• Manual setup (copy both files into ~/.cursor/)

See the Cursor hooks docs for details on user-level vs enterprise-level vs project-level hook configuration.

Test plan

• cargo test — all 21 tests pass including new test_cursor_breadcrumb_format
• End-to-end: ran hook to write breadcrumb, then aittributor --debug confirmed Cursor detected via breadcrumb path
• Verified detection works when Cursor is closed (breadcrumb persists, process scan misses — only tier 4 fires)

[alecthomas]

Seems reasonable, but getting the hook installed will be the trick.