"This needs a rebase" is a contribution: closing the loop with the author

The observation

When a pull request no longer fits trunk, the contributor who discovers it has not hit a dead end — they have produced the single most useful piece of information a stale pull request can receive. Every open good-first-bug carries a patch; the newcomer's real job at an event is testing and refreshing them; and "this no longer applies against current trunk" is precisely the refresh signal an author needs. Today the app treats that discovery as a failure to apologise for. It is a contribution to hand over.

The idea

Two halves, one cheap and one meaningful:

• Before: the pull request's own mergeability, as its host already computes it, shown as a small honest badge on the pull request card — needs a rebase — before the contributor spends a click. No local computation, no guessing; just surfacing a fact that already exists. Where the app's own evaluation (#351) and the badge disagree, the badge wins the display and the disagreement is worth logging, because the host's verdict is the one the author will see.
• After: when the contributor's own attempt lands in conflicts (#353), the app drafts the comment for them — which trunk it was tried against, which files no longer fit — ready to review and post on the pull request. The contributor's first interaction with a stranger's work arrives shaped like help, because it is help. The draft is a draft: the contributor reads it, owns it, and sends it themselves.

This piece has no dependency on the merge engine for its first half and could ship ahead of everything else in #350. It is also the part of the whole design that is most literally the product's mission: it converts a newcomer's frustrating afternoon into a comment an author will thank them for.

Deliberately not proposed

Posting anything automatically, ever. The comment is the contributor's, written in their name, sent by their hand. The app's job ends at making the good action the easy one.

Related

• #350 — the contract
• #353 — where the "needs a rebase" discovery is made
• #290 — the flow whose failures this turns into contributions

Start by reading the pull request flow in #290, then review the contract in #350 and the conflict discovery in #353. Check how the host's mergeability reaches the pull request card and how conflict details are available; done means showing the honest rebase badge and preparing a contributor-reviewed draft comment without posting automatically.