#27561 fix(sidebar): every trailing mark and control on one column and one slot pitch

Leo, 2026-10-29: "I SAID THE SHIT WAS MISALIGNED LAST FUCCKING NIGHT ... I ALREADY FUCKING LAID OUT THE DETAILS LAST NIGHT ... FUCKING JUST DO IT"

What was misaligned on the sidebar's right edge (a hovered row's ⋮ ⌄ ✕ above rows with unread dots and the red ⓘ):

• A hovered workspace row stepped 22 pt from its ✕ to its ⌄ (the column's space2 gap), then 20 pt to its ⋮. A group header steps 20 pt (controlSize + space1). So a row's ⌄ and ⋮ sat 2 pt left of the header's ⋮ and + above them.
• The row badge (unread dot, error ⓘ, stack) floored its x to whole points. At a fractional sidebar width (any dragged width) its dot sat up to 1 pt left of the ✕ and the header chevron above it.
• A listed tab's unread dot next to its status sat at an ad hoc space2 gap, not on the next slot.

The fix:

• SidebarStyle.trailingSlotPitch (controlSize + space1) and trailingSlotCenterX(rowWidth:slot:). Slot 0 is the trailing column. Each slot to its left steps one pitch.
• Controls left of a column mark start one controls' gap (space1) from the column's slot. A mark wider than the slot (a stack) keeps its space2 gap.
• The row badge snaps to the device pixel grid instead of flooring.
• A tab's dot beside its status takes slot 1.
• A group header's ⋮ and + center on slots 1 and 2. In comfortable density its 20 pt buttons used to step 21 pt, a point off a hovered row's ⌄.
• A row with nothing to disclose (workspace tabs on, no tabs) keeps no hidden chevron slot, so its hover ⋮ takes slot 1 instead of slot 2 beside an empty one.
• The .even close spot's shift applies only when the mark sticks out of the column slot, so it no longer moves a cluster that already sits on the grid.

Test: SidebarTrailingSlotTests, every density at widths 220.5, 247.25, 263.75 and 301.5 pt.

• Every row kind's trailing mark is on the column within half a backing pixel.
• Every hovered control, on rows and group headers, is centered on column - slot × pitch.
• A tab's dot beside its status takes slot 1.

Red at the test commit: the hovered ⌄ is at 181.5 against slot 1 at 183.5, and the tab dot is at 187.5 against 183.5. Green at the head, together with SidebarTrailingColumnTests, SidebarRowTrailingStatusTests, SidebarTabGroupControlsTests and SidebarTabLineTests (fleet runs at head and at base).

Grid: the trailing column is the existing trailingColumnCenterX line (horizontalInset + controlSize/2 from the row's end), which every mark and the header chevron already share. Second-and-further marks step trailingSlotPitch. Leading lines and row pitch: leading not mine.

Risk: small. Geometry only on the sidebar's trailing controls, at most 2 pt. No behavior change.

Before (base c00c3219):

Light	Dark

After (head 03932523): the dots and the ⓘ sit on the column (nearest pixel, not floored). The hovered-row step (22 pt to 20 pt) is in the test numbers above; the capture's pointer cannot hover a badge-preview row.

Light	Dark

Agent session: agent session

🤖 Generated with Claude Code

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Summary by cubic

Fixes sidebar trailing controls so hovered row buttons (⋮ ⌄ ✕), row badges, and tab dots all sit on one column and slot grid instead of drifting up to 2 pt off alignment.

• Adds trailingSlotPitch and trailingSlotCenterX so every control snaps to the same slot spacing the group headers already use.
• Centers a hovered group header's ⋮ and + on the same slots, and drops the hidden chevron slot on rows with nothing to disclose so their hover menu takes slot 1.
• Snaps row badges to the nearest backing pixel instead of flooring to whole points, which put unread dots up to 1 pt off the column at fractional sidebar widths.
• Places a tab's unread dot next to its status on slot 1 rather than an ad hoc gap.
• Applies the .even close-spot shift only when a mark sticks out of its column slot, so already-aligned clusters don't move.

Migration
Geometry-only change to the sidebar's trailing controls, at most 2 pt. No behavior changes. Adds SidebarTrailingSlotTests covering every density at fractional widths.