Attach an existing PR chip to a session that didn't open it

Problem

When a Claude Code session opens a PR, it renders as a rich interactive PR chip in that session. But when a different session only references that same PR (by URL/number) after the fact, it shows up as a plain markdown link — no chip.

This comes up naturally with parallel / forked sessions: work gets split across sessions (e.g. a background task or a second worktree actually opens the PR), but I'm monitoring or continuing from another session where I'd like the same rich PR chip — status, checks, review state — inline.

Request

A way to attach/pin an existing PR to the current session so it renders as the full rich chip, e.g.:

• an explicit affordance ("add PR to this session" by URL/number), and/or
• auto-upgrading a bare GitHub PR URL in the transcript into the rich chip.

Ideally generalize to other artifact chips (issues, CI runs) that were created in a sibling session.

Why it matters

Forked/parallel workflows are increasingly common, and the artifact chips currently live only in the session that happened to create them, which fragments visibility across a single logical piece of work.