Preserve cached PR pane links on completed labels

[f1sherman]

Summary

Preserve cached PR links when repo cleanup keeps a completed tmux window label.

Why

Brian noticed Pi/tmux sessions could keep the completed PR label but lose the clickable PR URL from the footer after cleanup. The root cause was that repo-end preserved the completed window label while unconditionally clearing the pane PR link state.

Approach

Capture the cached pane link before clearing worktree state and restore it only for the completed-window-label path when it came from the PR-status cache.

Related PRs

• Introduced by: Preserve tmux status label after repo-end #255
• Related: Fix tmux pr pane link cache #227
• Related: Show only the clickable PR URL first in tmux pane border #254

Verification

• Verified the tmux label contract now covers and preserves completed-window PR links.
• Verified pane-link behavior and CI test inventory still pass.

Reviewer Notes: Review found no actionable correctness issues.

[f1sherman]

Pull Request Review

• Reviewed at: 2026-07-04T23:17:10Z
• Reviewed head SHA: 16f047c5d9ac6dbb239d4c299865fbf549f9d656
• Risk: low
• Merge OK: false
• Verdict: patch is incorrect
• Confidence: 0.86
• Priority counts: P0=0 P1=0 P2=1 P3=0
• Inline findings posted: 0
• Unplaced findings: 1

The code change itself is narrowly scoped and the relevant pane-link test passes; tests/tmux-label-contract.sh could not complete in this environment because jq is missing. The remaining actionable issue is PR metadata required for regression fixes, not a code-level defect.

Unplaced findings

• [P2] Add root-cause PR context Because this is a regression fix, the PR description should identify the introduced-by or root-cause PR, or explicitly state Introduced by: unknown after checking. The current Related PRs entries are only marked as related, so future agents cannot tell which prior change created the cached pane-link cleanup regression.

[f1sherman]

Pull Request Review

• Reviewed at: 2026-07-04T23:17:10Z
• Reviewed head SHA: 16f047c5d9ac6dbb239d4c299865fbf549f9d656
• Risk: low
• Merge OK: false
• Verdict: patch is incorrect
• Confidence: 0.86
• Priority counts: P0=0 P1=0 P2=1 P3=0
• Inline findings posted: 0
• Unplaced findings: 1

The code change itself is narrowly scoped and the relevant pane-link test passes; tests/tmux-label-contract.sh could not complete in this environment because jq is missing. The remaining actionable issue is PR metadata required for regression fixes, not a code-level defect.

Unplaced findings

• [P2] Add root-cause PR context Because this is a regression fix, the PR description should identify the introduced-by or root-cause PR, or explicitly state Introduced by: unknown after checking. The current Related PRs entries are only marked as related, so future agents cannot tell which prior change created the cached pane-link cleanup regression.

[Agent] Updated the PR description with root-cause context: Introduced by: #255, plus related links for the PR cache and URL-only display work.