bug: xrpc request failed for invalid patch, lacking ui #325

There is no indicator in the UI for why hitting a button fails, like how it did for this merge attempt. Firefox devtools open to show a merge button's response is xrpc request failed On the server side, this was the output:

2025/12/10 08:04:52 ERRO knot/server/xrpc: failed to merge handler=Merge
 error=
 │ patch application failed: error: src/components/Post/MastodonHtmlContent.tsx: does not exist in index
 │ error: src/lib/strings/html-sanitizer.ts: does not exist in index
 │ hint: Use 'git am --show-current-patch=diff' to see the failed patch

The invalid patch was probably accepted during the creation of the pull request, so that's also an important bug.