desktop: clicking compressed session tabs doesn't switch when many tabs are open #61396

Summary

On the desktop app's new UI layout with top horizontal session tabs, once enough tabs are open that the tab bar overflows, each tab is compressed down to a ~28px icon-only chip. The tabs become visually unusable and clicking a tab no longer switches to its session — I can click but nothing happens (no accidental closing, no switch). This makes the tab bar unusable the moment it overflows.

This is distinct from the "close button misclick / accidentally closes a tab" complaints (#50196, #52044): here the tab is not being closed, it's just not selecting when clicked.

Environment

• opencode version: 2.2.2 (OpenCode.app / desktop client ai.opencode.desktop)
• OS: macOS 27.2.0 (arm64, Apple Silicon)
• Terminal: N/A (desktop client, not the TUI)
• Shell: /bin/zsh
• Install/channel: Desktop client, latest stable build
• Active plugins: None found in config

Reproduction

1. Launch OpenCode Desktop and enable the new UI layout (settings that puts session tabs in the top title-bar tab strip).
2. Open / create enough sessions that the top tab bar overflows the window width (roughly 8–10+ tabs).
3. The tab bar stops fitting and each remaining tab shrinks to an icon-only chip.
4. Click one of the compressed (non-active) tabs to switch to it.

Expected Behavior

Clicking a tab selects/switches to that session. When tabs don't all fit, a browser-like behavior: tabs keep a usable minimum width and the strip scrolls horizontally so every tab stays clickable.

Actual Behavior

• Tabs shrink to ~28px icon-only chips; their titles are hidden (only a 16px project avatar / status dot shows).
• Clicking a compressed tab does not switch to it — the click registers but the active session does not change ("点不动").
• There is no reliable way to reach or select the overflowed tabs: the strip has no horizontal scroll and no wheel-to-scroll-x, so on a standard (non-trackpoint/vertical-scroll) mouse the far tabs can't be reached.
• The close button overlaps the tab's click region (it's centered on very narrow tabs and present-but-transparent on 45–64px tabs), which compounds the "click does nothing useful" feel. (This is a secondary effect, not accidental closing.)

Suspects in the current source (for maintainers)

Working from the dev branch checkout of packages/app:

• Tabs are allowed to shrink to a tiny icon size. tab-strip.tsx (SessionTabSlot/DraftTabSlot, ~line 75 & 364): class="... w-56 min-w-7 max-w-56 flex-shrink" — min-w-7 is 28px, so with overflow each tab collapses to a 28px chip. tab-nav.css then hides the title and centers the close button in the @container (44px < width <= 64px) / @container (max-width: 44px) ranges.
• No horizontal scrolling of the title-bar strip. The strip is overflow-x-auto with no-scrollbar (tab-strip.tsx, TitlebarTabStrip), but unlike the side-region strip there is no wheel→scrollLeft handler wired on the title-bar tab strip (cf. runtime/plugin/tab-strip-scroll.ts, which the side panel uses). So an overflowing strip can't be scrolled on a vertical-mouse.
• Close button intercepts the click. tab-nav.css: for <=44px tabs the close container is display:none for inactive tabs but present/centered for the active tab, and for 45–64px it is opacity:0 (still hit-testable). tab-nav.tsx navigates on mousedown of the tab link; when a transparent/centered control overlaps that region, the click doesn't reach the link.

Additional Context

Reproduced on Desktop 2.2.2. Frequency: consistent whenever the top tab bar overflows. Workaround that works: switch to vertical / side tabs (Settings → Appearance → Tabs), or use the "Search sessions" / ⌃⇧⌘T commands, or shrink the tab count.

Related reports (the misclick / close-button framing, not the no-select framing of this one):

• In a view with many projects, it is almost impossible to switch tabs without closing them. #50196 — "In a view with many projects, it is almost impossible to switch tabs without closing them."
• Opencode Desktop's Close button is easily misclicked when trying to switch to another session tab #52044 — "Close button is easily misclicked when trying to switch to another session tab" (closed not_planned; suggested Chrome-like behavior).
• [Bug]: New UI horizontal tab bar unusable on mobile with 4+ sessions — only close button clickable #38974 — same class of symptom on the old UI, closed with v1.