The flex-1 row wrapper (titlebar.tsx) was missing min-w-0, so its auto min-width grew to the full intrinsic width of all tabs. With the header set to overflow-visible, that overflow shoved the trailing controls past the viewport edge (measured: right controls at x≈2969 in a 1600px window).
The inner tab list used overflow-hidden, so overflowing tabs were simply clipped with no scroll affordance.

Add min-w-0 to the flex-1 row wrapper so it shrinks to the header width instead of growing to its content. This keeps the right-side controls inside the viewport.
Change the inner tab list from overflow-hidden to overflow-x-auto (with scrollbar-width: none + ::-webkit-scrollbar hidden) so the tabs area is horizontally scrollable without a visible scrollbar.
Add shrink-0 to TabNavItem so tabs keep a readable width and scroll rather than squishing.

Before: right controls measured at x≈2969–3005 in a 1600px-wide window (off-screen).
After: right controls measured at x≈1547–1587 (on-screen), and the tab container reports as horizontally scrollable.
bun turbo typecheck passes (also enforced by the pre-push hook).
oxlint reports 0 errors on the changed file (only pre-existing warnings), and Prettier formatting is clean.