Add deterministic attribution footer to issues and PRs created on behalf of users

[dcramer]

When Junior creates a GitHub issue or PR on behalf of a user, there is currently no indication the content was AI-generated. This matters less as a credit attribution and more as a slop warning — a signal to reviewers that the content may not have been carefully written by a human.

Why not prompt steering

Prompt-level instructions to append a footer are non-deterministic: the LLM can skip or drop them. Attribution needs to be enforced in code, not in the model context.

Candidate approaches

• Tool/plugin wrapper (preferred): Intercept gh issue create / gh pr create calls in the GitHub plugin layer and append a footer (e.g. _Created via Junior_) to the body argument before the API call is made. The LLM never sees or controls this.
• Post-creation hook: After a successful create, immediately edit the body or post a comment. Slightly weaker (two-step) but still deterministic.
• Egress middleware: If an HTTP interceptor exists on outbound GitHub API calls, modify the request body there. Same guarantee, different insertion point.

Notes

• Issues filed under a user's OAuth token already carry their name — the footer is purely a content provenance signal.
• PRs have a partial equivalent via commit co-authorship, but the PR description body has the same gap.
• The footer should be minimal: a single line, e.g. ---\n_Created via [Junior](https://github.com/getsentry/junior)_.