Request: Allow Fix on merged PRs to start from target branch

Type: enhancement
Summary
When I click Fix on a code-review bug but the PR was already merged (and the source branch deleted), the fix should start from the target branch the PR was merged into.

Why it matters
This mirrors common workflows after merge and avoids manual branch recreation.

Expected
Fix detects the PR is merged and automatically creates a new working branch off the merge target.

Actual
Fix tries to resume from a deleted branch, requiring manual work.