feat(tui): make an expanded accordion's whole region the click/hover target

[Jiahao01121]

What

When an accordion block (reasoning, tool results) is expanded, its entire region — the title row and every disclosed content row — is now the click target that collapses it, and hover highlights that whole region. Previously only the title row was clickable.

A collapsed block is unchanged: its header row stays the only target, since its compact body rows are its own content rather than a disclosure affordance.

QA

https://cleanshot.com/share/DpTzZhCG

Details

• HeaderAt becomes AccordionAt — the target is no longer only the header, so the name moved with it. Hit-testing stays in chat.List; components.Accordion remains a dumb glyph renderer.
• Hover paints per row inside renderSurface, reusing PaintRowBackground so each line's own foreground colors survive the repaint. It never touches Document() or item heights.
• Two tones, matching the mockup: the header keeps accordionHover, and disclosed rows get a new accordionDetailHover token — accordionHover blended at 45% over the background (#1C1E26 dark, #D7DCE5 light). The header stays the region's visual anchor.
• The hand pointer follows the whole region for free: reconcilePointerShape derives from List.Hovered, which now resolves through AccordionAt.
• A block whose header has scrolled above the viewport still collapses when a visible disclosed row is clicked — the span's header index is left unclamped so the paint loop can tell whether row 0 is the header, while the row span itself is clamped to the viewport.
• Drag-select still wins: the toggle stays deferred to mouse-up and fires only when the gesture never became a selection range.

Test plan

• go build ./..., ./scripts/test.sh, ./scripts/lint.sh — all clean.
• TestAccordionAtCoversTheExpandedBlockAndNothingElse — expanded rows are targets, a collapsed block's body rows are not, nothing past the viewport is.
• TestAccordionAtKeepsExpandedDetailRowsAfterTheHeaderScrollsOff — the header is not the hit-test anchor.
• TestHoverPaintsTheWholeExpandedBlock — header fill on row 0, detail fill below, no leak past the item's last row.
• TestMouseMotionSetsHandPointerAcrossTheWholeExpandedRegion — hand across every disclosed row, default outside.
• TestMouseWheelScrollRefreshesHoverUnderTheStationaryPointer was re-aimed rather than deleted: it previously asserted that scrolling cleared hover, which assumed header-only targets. It now asserts hover is recomputed to a different block under a stationary pointer, which is the behavior it was really guarding.

Note for review

internal/tui/styles/palette.go shows a large diff because gofmt re-aligned both palette literal blocks when the new field widened the longest key. The only substantive changes there are the one new struct field and its two values.

[datadog-official]

Collapsed tool blocks with compact previews now highlight non-clickable body rows when their header is hovered. The hover span needs to remain header-only until the block is expanded.

_{Open Bits AI session}

_{🤖 Bits Code Review · Commit 19e8845}

[jinroh]

LGTM !

Added a little followup in 0646970 to make the full tool block clickable for tools with guttered preview block (edit tools and exec). Let me know if that looks good to you.

[jinroh]

rebased on top of main.