Sibling of tangled_pr.py. GET/POST /{owner}/{repo}/pulls/{n}/edit (htmx, session
cookie); does not mint a round or touch the patch; re-fetches the form after POST
and verifies the appview holds the new text. Built and proven by the
rust-pr-desc-concise pass (see machine-docs/PR-DESC-CONCISE.md).
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BMb31Hx9mnYGRXZ3AL68sk
