Perspective grid: docs say a constrained move snaps only within a quarter cell

A constrained move keeps only the snap correction along its direction, and that correction exists only when an edge ends within a quarter cell of a gridline. When no edge on those axes is that close, the move does not snap.

docs/mcp.md

@@ -7479,9 +7479,10 @@ back). Holding Shift during an in-plane move constrains each object's displaceme
 own plane. `perspective.move` accepts `constrain: true` (default false) and adjusts Snap to Grid along the constrained
 direction on the first object's plane and depth. With Snap to Grid, an in-plane move moves every object on the first
 object's plane by the same plane offset, whatever its depth. Without `constrain`, on each axis, the edge of their joint
-bounds nearer a gridline lands on it when that edge ends within a quarter cell of the gridline. With `constrain`, a
-horizontal or vertical move lands only the edge on its own axis, and a 45° move lands the edge on the axis whose nonzero
-correction is smaller. A perpendicular move does not snap.
+bounds nearer a gridline lands on it when that edge ends within a quarter cell of the gridline. With `constrain`, an
+edge also lands only when it ends within a quarter cell of a gridline: a horizontal or vertical move can land only an
+edge on its own axis, and a 45° move lands the edge on the axis whose nonzero correction is smaller. When no edge on
+those axes is that close, the move does not snap. A perpendicular move does not snap.
 `press_key` Escape during a move, a resize or a plane widget drag cancels it and puts the objects and the
 grid back. The arrow keys nudge a selection in perspective by the keyboard increment (`perspective.nudge`; Shift ×10, Alt
 copies). Object › Transform › Transform Again repeats the last perspective move or scale in plane space.

docs/target-app-parity.md

@@ -1535,7 +1535,7 @@ Moved from the ROADMAP's "Shipped so far" on 2026-10-10. Update it when a featur
   An Alt-drag of objects in perspective with the Perspective Selection tool, and an Alt-drag of a plane widget with that tool or the Perspective Grid tool, copy the objects on the first move, and the moves after it move those copies (#1429).
   With the Perspective Selection tool, Ctrl+Alt-drag (Command+Option-drag on macOS) also copies objects on their perspective plane; Alt/Option-drag continues to do so.
   With the Perspective Selection tool, holding Shift while moving or copying constrains each object's displacement to the nearest axis or 45° diagonal of its own plane; releasing Shift resumes the raw pointer position, and 5 still moves perpendicular to the plane. Snap to Grid follows the constrained line on the first object's plane and depth.
-  With Snap to Grid on, a move of objects on one perspective plane at different depths moves them all by the same offset on the plane, so they keep their spacing. Without Shift, on each axis, the edge of their joint bounds nearer a gridline lands on it when that edge ends within a quarter cell of the gridline. With Shift, a horizontal or vertical move lands only the edge on its own axis, and a 45° move lands the edge on the axis whose nonzero correction is smaller. A move perpendicular to the plane does not snap. Regression: `snap_moves_objects_at_different_depths_by_one_plane_offset` in `crates/engine/src/tests/persp_select.rs`.
+  With Snap to Grid on, a move of objects on one perspective plane at different depths moves them all by the same offset on the plane, so they keep their spacing. Without Shift, on each axis, the edge of their joint bounds nearer a gridline lands on it when that edge ends within a quarter cell of the gridline. With Shift, an edge also lands only when it ends within a quarter cell of a gridline: a horizontal or vertical move can land only an edge on its own axis, and a 45° move lands the edge on the axis whose nonzero correction is smaller. When no edge on those axes is that close, the move does not snap. A move perpendicular to the plane does not snap. Regression: `snap_moves_objects_at_different_depths_by_one_plane_offset` in `crates/engine/src/tests/persp_select.rs`.
   When the desktop app opens a document on a thread of its own (#1245), that thread also reads the document's linked files and lays out its type, and the UI thread only adds the finished document: in release builds, the step left on the UI thread takes 0.02 ms instead of 1.04 s for a document with 12 linked 3000 × 2000 TIFFs, and it takes 0.1 ms instead of 0.85 s for one with 300 Auto Size area type objects, every second one in three columns.
   Laying out type keeps each font face's shaping plans, at most 32 per face, so type objects of the same font, script, direction, language and features share one plan: the layouts of a document of 5,000 short point type objects take 59 ms instead of 73 ms in a release build, and the glyphs, bounds and baselines do not change.
   Laying out type looks up the font face of each style run once and uses it for the run's glyphs and for the line metrics of a paragraph that starts in that run: the layouts of a document of 5,000 short point type objects take a median of 215 million CPU cycles instead of 236 million in a release build (11 alternating runs of each build on Windows 11, measured while other builds were running), and the glyphs, bounds and baselines do not change.