fix: preserve linked PRs and show them in badge tooltips

[Bil0000]

When a thread shows the PR inferred from its branch, linking another PR hides the first one because only the new PR is saved. Save the displayed branch PR with the new manual link so both remain linked. Repeated links stay unique, and linking another PR does not restore a PR removed while other links remain.

Multi-PR and stack badge hovers now use the same compact status, number, and title rows as the thread hover. This shared control covers the sidebar and composer footer; single-PR behavior is unchanged.

Validation: 110 focused tests passed, including branch inference, repeated links, unlinking, and projection rebuilds. Web and server type checks passed. Targeted lint passed with existing warnings. Browser checks passed at 1280px and 390px, including mouse hover and keyboard focus. The shared server fix applies to all clients; the UI change applies to web and desktop.

Before and after images use synthetic data.

The PR includes the same small CI repair used by the related V2 feedback PRs: remove unused exports, exercise conversation-only rollback in shared-workspace fixtures, and test checkpoint inspection without routing it through the feed that hides checkpoints. All 170 affected tests pass (one existing skip), and the scoped export check passes. Runtime file-restore safety is unchanged.

Model: GPT-6. Harness: Codex.

[macroscopeapp]

Approvability

Verdict: Approved at a923ef9

Macroscope's review found this PR approvable — This is a focused pull-request state fix and small UI presentation update: manually linking a PR now retains the discovered branch PR, while existing badges can show their persisted linked-PR list. Other edits are test-only, cleanup, or import/type maintenance, with no schema, deployment, security, or default changes.

Notes:

• No code objects were reviewed. Approvability was decided on eligibility alone.

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Dismissing prior approval to re-evaluate dafa593