bug(ask): stale transcript frame bleeds into ask_user_question dialog right after reading an image

[grivper]

Description

When an image was just read/attached into context (e.g. via the read tool on a screenshot) and an ask_user_question dialog is triggered immediately after, the dialog renders with leftover content from the previous transcript frame bleeding through above/around it (stray divider lines, fragments of earlier chat text) instead of a clean redraw. It self-corrects as soon as any redraw-triggering interaction happens (scroll, resize, moving focus).

Steps to reproduce

1. In a fullscreen session with the sidebar active, use read on an image file so its preview/reference card renders in the transcript.
2. Immediately trigger a tool call that opens ask_user_question.
3. Observe stale content (old transcript lines, divider artifacts) overlapping/bleeding into the area where the question dialog renders.
4. Interact with the UI (scroll, resize) — the glitch clears and the dialog renders correctly.

Expected behavior

The ask_user_question dialog should render on a fully cleared/fresh frame regardless of what was rendered immediately before it (image card or otherwise).

Screenshot

Not embedded here — the GitHub REST API used to file this issue cannot attach images. I have a screenshot showing the question dialog rendering below leftover chat content and stray vertical divider lines that don't belong to the current frame; can add it as a comment via drag-and-drop.

Possibly related

Likely connected to #1141 (fixed) / #1274 (merged 2026-09-20, the day before this was observed): ask_user_question was just changed from an overlay to a "dock-swap" mount specifically so the transcript stays scrollable while a question is on screen. This stale-frame bleed-through right at that same mount point, triggered specifically after an image card renders, looks like an edge case not covered by that very recent change rather than a long-standing issue.

Possibly related code

Likely related to the same frame/section caching in lib/shell-sidebar-layout.ts (prepared/sectionCache, "reuses its last frame until something it paints changes") not being invalidated when an image-bearing tool result is followed by a dialog-owning component. Could also be a pi-tui core interaction rather than something owned by gentle-pi — worth flagging as possibly cross-cutting.

Environment

• Package: gentle-pi (repo: gentle-shell)
• Fullscreen mode, sidebar active, 140+ columns
• Trigger: ask_user_question fired right after an image read

[grivper]