A session row can say whether its work is open, merged or closed, and link
to it. The join is the session's own repo + branch, asked of GitHub in one
batched GraphQL request per repo (branch aliases, not a `gh pr list` page
that a busy repo crowds ours out of), through the remote-aware git facade so
a desktop on a remote gateway asks the backend's `gh`.
Two ways a session's branch can't answer, both covered:
- It ran on trunk. Fork PRs share our branch namespace, so asking about
`main` badges a stranger's PR onto it — trunk is never asked about, and
cross-repository PRs are dropped server-side either way.
- It worked in a worktree, so the branch it recorded at start isn't where
the PR came from. Creating a PR from the review pane binds the session to
the branch it actually used, and for sessions that predate that, the PR is
recovered from the transcript: `gh pr create` prints a bare PR url and
nothing else, so a tool result whose whole output is one is a claim rather
than a mention. Scanned read-only across profiles, once per session ever.
