Sidebar overlay hides chat content and interrupts session switching — poor UX in Desktop v1.18.15 #41203

Summary

Since upgrading to Desktop v1.18.15, the left sidebar has become a floating overlay (absolute + z-30) instead of a persistent column that pushes content. When the sidebar is opened, it covers the chat area instead of shrinking it, which frequently hides the active session and interrupts session switching. The experience feels very janky.

Environment

• OpenCode Desktop v1.18.15 (macOS)
• Regression: this worked fine in earlier versions where the sidebar occupied layout space and the chat area reflowed around it.

Repro steps

1. Open OpenCode Desktop v1.18.15 with a project containing several sessions.
2. Toggle the sidebar on (button in the titlebar or Cmd+B).
3. Switch between sessions/projects in the sidebar.
4. Observe: the sidebar overlays the chat panel, covering the conversation (especially with narrow windows). Hovering to "peek" (sidebarHovering / peeked state) can also pop the sidebar over the chat unexpectedly.

Expected behavior

• Option A (preferred): Sidebar should remain a static in-flow column that pushes the chat area (like older versions), so switching sessions never hides the conversation.
• Option B: Make the overlay/compact mode configurable (e.g., ui.sidebar.mode: "dock" | "overlay", or a persistent width setting), defaulting to dock.

Impact

• Frequent visual hiding of the active session forces extra clicks to restore context.
• The hover-peek behavior triggers unintentionally during mouse movement, causing flicker and accidental navigation.

Suggestion

Offer a config option like ui.sidebar.enabled / ui.sidebar.mode to keep the docked layout. Related: #40086 (persistent sidebar toggle request).

Notes

• Happy to provide screen recordings or window-size details if helpful.