Attempt to make a layout engine that takes the topology and LayoutSpe…

[pragmatrix]

…cs from external sources and layouts incrementally

[Copilot]

Pull request overview

Introduces an incremental layout engine that can recompute geometry based on an external topology + algorithm, and wires it into the desktop system to replace the prior “build full layout tree then place” approach.

Changes:

• Added IncrementalLayouter (with LayoutTopology / LayoutAlgorithm) to support incremental measure/place and emit only changed rects.
• Switched DesktopSystem layout application to use incremental recomputation and removed the separate rects cache.
• Refactored OrderedHierarchy to store hierarchy relationships in a single node-state map (parent + ordered children) and added exists().

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
layout/src/lib.rs	Exposes the new incremental layouter module publicly.
layout/src/incremental_layouter.rs	Implements incremental recompute, caching, eviction, and unit tests.
desktop/src/desktop_system.rs	Replaces old layout building/placing with incremental recompute + change application; integrates hit testing + rect lookup with the layouter.
desktop/src/aggregates/ordered_hierarchy.rs	Consolidates hierarchy state into a single nodes map and adds exists() for topology queries.
.github/copilot-instructions.md	Documents new guidance around single source of truth, hierarchy representation, and invariant handling.