feat(ui): New tab always opens a new tab

[rigel-mintaka]

This PR is part of a stack containing 3 PRs:

1. main
2. feat(ui): stack the agent log panel in narrow panes #1787
3. "feat(ui): New tab always opens a new tab" (this PR)
4. fix(ui): keep the Bridge Issues/PRs toggle in place #1812

Summary

Applies Matt's ruling B on RIG-4676: New tab (W N, and the palette's "New tab") always opens a new Bridge tab, even when Bridge is already open.

• The open layout action gets an optional fresh flag that skips the same-path dedupe. Only tab.new sets it.
• Links, Mod+click and deep links still dedupe to an open tab.
• The 10-tab cap still applies. A fresh open at the cap is refused with the layout notice.
• The design record is frozen, so the ruling goes in as ledger row DL-409, which amends DL-390's dedupe clause for this command only. DL-409 was claimed from the shared counter (tools/dl-claim).

Verification

• Red first: three tests failed before the fix and pass after:
  • the reducer's fresh open of an open path;
  • the reducer's fresh open at the cap;
  • New tab on the Bridge tab, run against the real store.
• compass-ui:test passes 1294; the 4 env-secrecy tests fail only because a jj workspace has no .git.
• typecheck, dev-smoke, visual-gate (15) and design-ledger-gate:check pass. Biome and rumdl are clean.
• Chromium smoke: on /#/, pressing W N takes the strip from 1 tab to 2, and the hash stays /.

Risks

• Duplicate Bridge tabs are now one keystroke away. Two tabs on the same path were already reachable before this change (open a tab, then navigate it to /), and every layout consumer keys by view id or tab id, not by path.
• With two Bridge tabs open, a plain open of / focuses the first one in tab order. This was already the behaviour before this change.
• Open PRs docs(repo): design — fail-closed Renovate relock for devenv locks (RIG-3253) #1746 and docs(server): link pull requests to issues (RIG-4034) #1749 name DL-409 in their bodies without claiming it from the counter. The counter issued DL-409 to this PR.

Compatibility

fresh is optional and defaults to false, so every existing open dispatch keeps its behaviour.

Documentation

Ledger row DL-409 in docs/designs/DECISIONS.md.

Ledger-impact: appends DL-409 (amends DL-390 for New tab).

Refs RIG-4676

[linear-code]

RIG-4676

[github-actions]

Compass engineering docs preview: https://compass-ux-4676-new-tab-fres.compass-eng-docs.pages.dev

Deployed from compass-ux/4676-new-tab-fresh at b86bcf8.

Changed pages:

• docs/designs/DECISIONS.md

[mattwilkinsonn]

/trunk merge --priority=high

[trunk-io]

😎 Stack merged successfully - details.