The tasks rail (from #104010) only rendered as a right-docked 230-280px
column and vanished with its toggles below a 1120px viewport, so narrow
split-view panes got a crushed thread and compact windows lost access
to background tasks entirely — the same bug class #104033 fixed for the
workspace rail and detail panel.
The rail now follows the pane's measured width: it presents as a
full-width bottom strip (sections side by side like the workspace
rail's bottom dock) when the pane is too narrow for a side column, and
the workspace rail keeps first claim on the side slot when only one
column fits. Side-docked rails, not bottom strips, now count against
the width available to the chat + detail split.
Proof: check:changed + 212 focused tests green on Testbox at this exact
content; codex autoreview clean; chromium+webkit visual verification at
seven window widths plus split view with zero geometry overlaps.
Landed with maintainer CI override.
Closes#104091
0ae3de7c6f
