The convention gate refuses edits to posts it did not shape

[ecv]

The convention gate measures a whole opening post every time anyone edits one, so a post written before the convention existed, or written by someone else, cannot be touched until it is rewritten to the current bar. That turns a one-word correction or a checkbox tick into either a rewrite of another person's words or a raw API call that skips the gate outright. The second is what happens in practice, which teaches everyone to route around the check rather than meet it. The gate should judge the change rather than the whole body, and pass any edit that leaves a post no further from the bar than it found it.

Ticking a criterion someone else wrote is the common case, and it is exactly the edit the gate should welcome.

Rewriting a colleague's issue to satisfy a formatting rule is worse than leaving it unformatted, so the current escape route is the only honest one available.

Acceptance criteria

• A post written before the convention can be edited without being rewritten first
• Someone else's post can be corrected without putting new words in their mouth
• An edit that leaves a post no further from the bar passes
• A new post still meets the full bar, and an edit that makes a post worse is still refused

Note

The workaround in use today is a direct API call, which is disclosed each time it is used. Closing this removes the need for it.