Source-scoped overlay invalidation

Definition

Source-scoped overlay invalidation means an overlay store can decide whether a document change affects a given decoration, annotation, or widget source before rebuilding all projected slices.

It is the layer between:

whole-store refresh
per-runtime-id subscription delivery

Why it matters

Slate v2 already has local subscription delivery. That is good, but it is not the whole perf architecture.

If every editor commit still makes every overlay source rebuild and every range projection walk the whole text tree, the UI may stay local while the projection engine still pays too much.

Required ingredients

operation-derived dirty paths
touched runtime ids
source dirtiness declarations
stable source identities
previous projection snapshots keyed by source and runtime id
fallback full refresh for unknown or broad sources

External pressure

ProseMirror pressures this through child-scoped decoration propagation.
Lexical pressures this through dirty leaf / dirty element updates.
VS Code pressures this through typed decoration/comment/widget channels and a view-model layer.
React 19.2 helps consume the result but does not replace this layer.

Non-goals

no public path-based widget anchoring
no new generic decorate callback
no claim that every external source can be perfectly incremental
no hidden stale overlays when a source cannot declare dirtiness safely