Cursor-reach reveal now fulfils the "Slide in on cursor reach"
description on the design's Hidden-on-hover layout card.
- BrowserCore::active_space_sidebar_width() returns the current
sidebar tier without cloning a full BrowserSnapshot, so the
mouse_move hot path stays cheap.
- on_window_mouse_move on the shell root hits-tests the cursor x
against REVEAL_THRESHOLD_PX (24 px from the left edge). Outside
the reveal/collapse zones it returns immediately, so 99 % of
mouse moves never even read the snapshot.
- When in HIDDEN mode and the cursor crosses the reveal threshold,
expand_hidden_sidebar fires (its early-return on already-expanded
state prevents notify spam). When the cursor passes
COLLAPSE_THRESHOLD_PX (shell inset + default sidebar width + 24 px
buffer), collapse_hidden_sidebar fires.
- Click-to-expand on the rail and click-on-backdrop-to-collapse
remain as predictable fallbacks.
ZacharyZhang-NY
4403eacf15