[reoring]

Why

The side panel showed one issue; clicking another on the list or board replaced it. Comparing two issues meant going back and forth.

What

Design: design/README.md § Issue panel tabs (v0.1.17).

• Each issue opened from a list, board, sprint or the inbox is a tab in the panel. Clicking an issue that is already open activates its tab.
• The active issue stays in the URL (?issue=), so links, reload and back/forward work as before. The open tabs are the person's working set: kept in sessionStorage per browser tab, never in the URL, at most 20 (least recently active evicted).
• J/K with the panel open replaces the active tab in place (no trail of tabs); walking onto an issue that already has a tab activates it instead. Browsing never closes a tab.
• Closing the active tab (its ×, middle click, Esc, Delete on the focused tab) activates the right neighbour, else the left; closing another tab leaves the active one alone; the panel's × closes all.
• Only the active issue is fetched and rendered.
• Rules are pure functions in web/src/model/panel-tabs.ts with table tests; usePanelTabs is shared by the issues pages and the inbox.

Unchanged: the command palette and links inside an issue (parent, children, blockers) still go to the full page.

Verification

• tsc --noEmit, bun test src (156 pass).
• Browser against the mock API (1440×900): three cards → three tabs; first card again → its tab active, still three; close a background tab → active unchanged; close the active tab → right neighbour; Esc on the last → panel closed, issue removed; reload restores the tabs; fresh ?issue=APT-9 → one tab; three tabs then J×4 → active changes, still three tabs; open A, B, Back → A active, both present; page scroll kept on tab switch; 12 tabs → strip scrolls, active tab in view; Home/Right/Delete on the strip; unknown issue shows not-found in a closable tab; inbox opens tabs. At 390px wide the strip scrolls and close buttons are 32px.
• Not verified: the deployed installation; a screen reader.