Trim per-release overhead in the scene

Only re-measure the viewport at begin() when a container is mounted, and
only allocate waiting machinery when an interrupted finish() actually
needs to wait for a later release. Interrupted releases now resolve with
the final decided outcome in every case.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Faarh2Ts6StJPcz2mRiHiR

packages/core-v2/src/scene/scene.ts

@@ -285,9 +285,12 @@ class Scene implements OriginScene {
    */
   /** The latest release (finish call) of each operation. */
   private readonly releases = new WeakMap<MutableOriginOperation, object>();
-  private readonly outcomes = new WeakMap<
+  /** Final outcome of each operation, once a release has decided it. */
+  private readonly outcomes = new WeakMap<MutableOriginOperation, boolean>();
+  /** Interrupted releases waiting for a later release to decide. */
+  private readonly waiters = new WeakMap<
     MutableOriginOperation,
-    { promise: Promise<boolean>; resolve(committed: boolean): void }
+    Array<(committed: boolean) => void>
   >();
   private readonly effectSets = new WeakMap<
     MutableOriginOperation,
@@ -322,7 +325,7 @@ class Scene implements OriginScene {
     originKey: string,
     action: OriginAction,
   ): Promise<OriginOperationHandle> {
-    this.refreshViewport();
+    if (this.container) this.refreshViewport();
     const operation = this.graph.begin(
       originKey,
       action,
@@ -383,36 +386,40 @@ class Scene implements OriginScene {
       current,
     );
 
-    const outcome = this.outcomeOf(operation);
+    // Another release already decided this operation.
+    const decided = this.outcomes.get(operation);
+    if (decided !== undefined) return decided;
     // A later operation may already have finalized this edge.
     const finished = (operation.phase as OriginOperationPhase) === "finished";
-    if (!this.graph.operation(operation.id) || finished) {
-      const committed = this.graph.operation(operation.id)
-        ? operation.intent === "commit"
-        : commit;
-      outcome.resolve(committed);
-      return committed;
-    }
-    // Caught by update() or superseded by a later finish().
-    if (!current()) return outcome.promise;
+    if (!this.graph.operation(operation.id) || finished)
+      return this.decide(
+        operation,
+        finished ? operation.intent === "commit" : commit,
+      );
+    // Caught by update() or superseded by a later finish(): wait for the
+    // release that decides.
+    if (!current())
+      return new Promise<boolean>((resolve) =>
+        this.waiters.set(operation, [
+          ...(this.waiters.get(operation) ?? []),
+          resolve,
+        ]),
+      );
 
-    const committed = commit
+    return this.decide(
+      operation,
+      commit
         ? this.graph.commit(operation.id)
-      : (this.graph.cancel(operation.id), false);
-    outcome.resolve(committed);
-    return committed;
+        : (this.graph.cancel(operation.id), false),
+    );
   }
 
-  /** Resolves with an operation's final outcome, whichever release decides. */
-  private outcomeOf(operation: MutableOriginOperation) {
-    let outcome = this.outcomes.get(operation);
-    if (!outcome) {
-      let resolve!: (committed: boolean) => void;
-      const promise = new Promise<boolean>((done) => (resolve = done));
-      outcome = { promise, resolve };
-      this.outcomes.set(operation, outcome);
-    }
-    return outcome;
+  /** Record an operation's final outcome and settle interrupted releases. */
+  private decide(operation: MutableOriginOperation, committed: boolean) {
+    this.outcomes.set(operation, committed);
+    for (const resolve of this.waiters.get(operation) ?? []) resolve(committed);
+    this.waiters.delete(operation);
+    return committed;
   }
 
   registerElement(nodeKey: string, element: HTMLElement | null): void {