Self-review checkbox: /improve publishes it, but nothing handles the tick #3808

Feature request

/improve publishes an author self-review checkbox when demand_code_suggestions_self_review = true (pr_code_suggestions.py:495-505 appends - [ ] {text} plus one of three hidden markers: <!-- approve pr self-review -->, <!-- fold suggestions self-review -->, <!-- approve and fold suggestions self-review -->). But nothing reacts when the author ticks it: the webhook branch that should handle the edit is a stub,

# pr_agent/servers/github_app.py:409-410
elif event == "issue_comment" and 'edited' in action:
    pass # handle_checkbox_clicked

and both halves of the designed reaction have no caller from this path:

• the fold rendering exists unreached: publish_persistent_comment_with_history(..., only_fold=True) (pr_code_suggestions.py:613, the if only_fold: branch at :732) — its only invocation passes only_fold=False (:621);
• the approve primitive exists unreached from here: auto_approve() (github_provider.py:2033, pr.create_review(event="APPROVE")) is only called from the /review flow (pr_reviewer.py:1577).

So demand_code_suggestions_self_review renders a dead checkbox, and approve_pr_on_self_review / fold_suggestions_on_self_review (configuration.toml:265-268) are advertised knobs with no reachable implementation.

Proposal

Handle the tick in the GitHub app:

1. In the issue_comment + edited branch, compare changes.body.from with comment.body: the self-review line flipped - [ ] → - [x] and the body carries one of the three self-review markers.
2. Verify the comment is PR-Agent's own suggestions comment (is_comment_authored_by_pr_agent, git_provider.py:895) and the editor (webhook sender) is the PR author (provider pr.user.login), so a bystander ticking the box cannot approve someone's PR.
3. Act per the marker: re-render folded via publish_persistent_comment_with_history(..., only_fold=True), and call auto_approve() when the marker says approve. Approving uses the same review API the app already uses for feedback, so pull_request_reviews: write should already hold — worth confirming on the app settings.
4. Unit tests with issue_comment edited payload fixtures: an author tick folds/approves per the marker; an edit that does not touch the checkbox is ignored; a non-author tick is ignored; a comment without a marker is ignored.

Scope: the GitHub app only, where the stub sits. The Action runner could share the same detection later via servers/github_common.py (the #3785 pattern), and other providers' servers can follow if they want the feature.

Motivation

The checkbox is the one human-in-the-loop affordance the bot already publishes; wiring it gives authors an explicit "I read the suggestions" gesture that folds the noise and (opt-in) approves the PR, and turns three documented config keys into working behavior.