Summary

• Keep the macOS tabbar new-session button in the flowing tab strip instead of pinning it as a fixed chrome tool.
• Reserve a stable new-button slot by subtracting the button width from themed AppChrome tab-list max width.
• Add a focused AppChrome regression test so the tab list cannot consume the new-button slot again.

Root Cause

After the command search button was pinned as a fixed chrome tool, themed AppChrome still let .tabbar__tabs use max-width: 100%. With enough tabs, the scrollable tab list consumed the whole tabbar width and pushed the flowing new-session button under the fixed search button.

Solution

The tab list remains scrollable, the new-session button still follows the rightmost visible tab, and the themed chrome tab list now reserves the new-button slot before the fixed search area.

Verification

• npm run check:css
• npx tsx src/__tests__/app-chrome-tabs.test.ts
• git diff --check origin/main-v2...HEAD