The sidebar stops spending columns on nothing, and a background tab says whose it is - #33

Two things reported while reading a frame, fixed separately and reviewable apart (one commit each).

1. The connection rail was too wide for what it holds

c9aa311. The demo's connections frame drew a 22-column sidebar whose widest visible row ended at column 20 and whose typical row ended at 15. Two of those columns named nothing:

• The indent ladder skipped a level. Worlds sat at indent 0, characters jumped to 2, windows to 3 — so every window row carried two cells of indent for a depth no row is ever drawn at. It is one level per depth now: world 0, character 1, window 2.
• RailMargin was 2. A divider column and a one-cell spacer already stand between the rail's last cell and the first pane, so the second margin cell separated nothing from nothing. It is 1.

The rail's width comes out of the pane area and every connected session is told its pane's size over NAWS, so both are columns handed back to the game. Demo connections: 22 → 19.

The reserved fields are untouched — the unsent pen, the unread badge and the chord column still cost their cells when empty, because a field that appears out of nothing resizes the sidebar from the wire.

Pins: RailModelTests.TheIndentLadderSkipsNoLevel (no row is more than one level deeper than the row before it) and RailWindowRowTests.TheRailSpendsAtMostOneBlankColumnPastItsWidestRow. One existing assertion had the old 4-cell indent baked into a string literal.

2. A background tab wore the wrong character's colour

6a32756. A pane can host several characters' windows as tabs and paints one rectangle, so the plane behind a strip can only ever answer for the window in front. Every other tab in that strip was drawn in that same hue — naming the wrong character, which is the one thing the pane tint exists to prevent.

TabControl's four chip colours belong to the control, so this cannot come from PaintTabChips. It goes where the per-tab channel is: the title, which is markup, where a tag costs no cells and moves no hit test. TabChip carries the plane and its ink; TabTitles.For emits [{ink} on {plane}] around the same span the bold and the activity tint already cover.

Three things hold it together:

• ChipFor runs the same pipeline as the plane behind it — SurfaceToneIn (the character's tint, plus the focus lift when the pane holds focus) then Recessed — so a strip whose tabs share an owner comes out byte for byte what it was, and only a mixed pane changes. PaneSurfaceTone is now one line of that same function rather than a second arithmetic beside it.
• The selected tab is never chipped: the strip already paints it in its page's plane.
• Unread stays a foreground over the chip, so "whose" and "something new" remain the two channels they are everywhere else.

A window nobody owns (the web view) and a character who has chosen no colour both come out on the plain surface rather than borrowing a neighbour's hue.

New tint-tabs snapshot view: the two tinted characters of tint with no split, so one pane holds both their windows. It is the only geometry where an idle chip can be seen wearing a colour the pane behind it is not. The frame reads Thistle ⌁ │ Corvid - Chat (2) │ ▌ Corvid with Thistle on Moss, Chat on recessed Slate and the selected Corvid on lit Slate.

PaneTintTests.ABackgroundTabWearsItsOwnCharactersColour reads the painted cells: the old code was internally consistent while the screen was wrong, so anything built on the expression would have passed. Confirmed it discriminates by temporarily resolving the pane's front window instead — it failed with expected Rgb(20,42,14), found Rgb(17,34,71). TabTitlesTests pins the markup's shape and that a chip costs no cells.

Verification

dotnet build SharpMUTerm.slnx warning-free, and all five suites green: Core 937, Graphics 83, Scripting 42, Web 37, Tui 1777.

🤖 Generated with Claude Code

https://claude.ai/code/session_015nuKnWthnELNkrd86q5KWN

Summary by CodeRabbit

• New Features

  • Tab chips now use each character’s tint, including distinct colors for idle tabs.
  • Unowned tabs use the neutral recessed surface.
  • Mixed-character tab layouts are supported in tint snapshot views.
  • Workspace rail indentation and width are more compact and consistent.

• Bug Fixes

  • Preserved selected-tab styling and unread indicators.
  • Corrected rail spacing and indentation behavior.
  • Improved tab title styling without affecting title width.