The rail was setFixedWidth, so the handle QSplitter draws between it and the
content was inert — it looked draggable and did nothing when dragged.
The expanded rail is now a range (132–360px) instead of one number, so the
handle has something to give. Collapsing still pins it at 54px exactly, and a
width dragged to is remembered across the fold rather than snapping back to the
150px default. Long project names and RECENTS threads are what a wider rail
buys.
check_rail_resize drives the splitter the way the handle does and asserts the
rail follows, clamps at both ends, folds to 54px and comes back to the chosen
width. Restoring setFixedWidth fails it — the first attempt at that mutation
passed, because setMaximumWidth on the next line quietly undid it.
16/16 checkers pass.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
