perf(canvas): stabilize renderer bindings and retain unchanged projections

src/lib/canvas-bindings/projection-cache.ts

@@ -0,0 +1,28 @@
+import type {Document,Id} from '../canvas-core/types.ts';
+import {equal,fault} from '../canvas-core/values.ts';
+import type {projectCanvas} from './projection.ts';
+
+type Projection=ReturnType<typeof projectCanvas>;
+type Retained<T>={incarnation:number;ownerCanvasId:Id;value:T};
+/** View-owned rendering cache, never a document store. Keep unchanged React Flow input identities. */
+export function createProjectionCache(){
+  let scope:object|undefined,projectId:Id|undefined,canvasId:Id|undefined;
+  let nodes=new Map<Id,Retained<Projection['nodes'][number]>>(),edges=new Map<Id,Retained<Projection['edges'][number]>>();
+  function retain<T extends{id:Id}>(document:Document,values:T[],previous:Map<Id,Retained<T>>){
+    const next=new Map<Id,Retained<T>>();
+    for(let index=0;index<values.length;index++){
+      const value=values[index],record=document.elements.get(value.id);if(!record)throw fault('projection_identity_missing',[value.id]);
+      const old=previous.get(value.id),retained=old&&old.incarnation===record.incarnation&&old.ownerCanvasId===record.ownerCanvasId&&equal(old.value,value)?old.value:value;
+      values[index]=retained;next.set(value.id,{incarnation:record.incarnation,ownerCanvasId:record.ownerCanvasId,value:retained});
+    }
+    return next;
+  }
+  return Object.freeze({
+    reuse(owner:object,document:Document,viewCanvasId:Id,projection:Projection):Projection{
+      if(scope!==owner||projectId!==document.projectId||canvasId!==viewCanvasId){nodes.clear();edges.clear();scope=owner;projectId=document.projectId;canvasId=viewCanvasId;}
+      nodes=retain(document,projection.nodes,nodes);edges=retain(document,projection.edges,edges);
+      return projection;
+    },
+    clear(){nodes.clear();edges.clear();scope=undefined;projectId=undefined;canvasId=undefined;},
+  });
+}