fix(explorer): the sweep box marks only rows it touches (#326)

[Maxaubert]

The owner, 2026-10-07, with a screenshot of a sweep box drawn in the empty space right of the Explorer's columns that had marked the rows beside it:

i can select files without having the highlight box be over the files, that should not happen. only the ones that are inside it, even if that's a px should get marked but this is not inside at all

Cause

The sweep's hit test (rowsInBand, called from useSweep) compared only the box's vertical span with the rows'. Any rectangle at a row's height marked it, wherever it was across, so a box drawn in the blank space beside the rows, or up the empty right side from under them, marked every row it passed level with.

Fix

• lib/marquee: rowsInBox takes the whole box and the row's drawn extent across. One pixel of overlap counts; a box starting at the row's right edge does not. Rows are still found by index, so rows scrolled out of view still count.
• useSweep hands the hit test the whole box. The row's extent (rowAcross) is measured once per sweep, not on every tick (review: a forced layout read each frame), and asked again only while no row is drawn.
• BrowseList measures the drawn row (the list's left to the end of its last column, Dragging: the whole row picks an item up, the cursor stays an arrow, and the box select starts only from empty space #320's gutter short of the edge) off any row in view, plus scrollLeft. The tree measures its own rows, which run its full width, so it behaves as before.
• Version 0.96.1.

Tests

• Unit: marquee.test.ts covers rowsInBox: a box right or left of the rows, below the last row, ending on the left edge, starting one pixel past, one pixel in, and rows far out of view.
• e2e marqueeEdge (new): a box beside the rows, and one up the empty right side from under them, mark nothing, live and after release; a box ending a pixel past the rows marks nothing; a box two pixels in marks the rows it spans. It failed 5 checks on the old code.
• marquee and marqueeQuiet: the sweeps that stayed beside the rows now reach into them.
• typecheck, lint, the unit suite and the three marquee e2e scenarios pass locally.

Closes #326

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https://claude.ai/code/session_01FHHaWKR4M5QtW7Wecyuk4t