Claude Session URL appended to commit messages and PR descriptions by default

Claude Code automatically adds a session URL (e.g. https://claude.ai/code/session_...) to the bottom of every commit message and PR description it creates, with no opt-in prompt, warning, or onboarding mention. Users only discover this after the URLs are already embedded in their git history, where they look unprofessional and clutter the record.

The feature request proposes making session URL attribution opt-in, ideally via a one-time onboarding prompt like "Would you like to include a link back to this Claude session in commit messages?" Alternative solutions include keeping it opt-out but showing a first-commit notice with a "Don't add this again" option, or removing it entirely and relying only on the existing "Co-Authored-By: Claude" trailer.

Users have found workarounds: the `attribution.commit: ""` setting in `.claude/settings.json` suppresses it but is effectively undiscovered, and a commit-msg git hook can strip it but doesn't always fire reliably in remote/cloud environments. The request is filed with priority Medium.