fix(core): mint guest-local runtime-data ids in a separate space from host ids

packages/core/src/runtime/runtimeData.test.ts

@@ -88,4 +88,24 @@ describe("runtime data registry", () => {
 
     expect(applied).toHaveBeenCalledTimes(1);
   });
+
+  it("never reports a composition-side delivery under a pending host request id", async () => {
+    const applied = vi.fn();
+    setRuntimeDataAppliedReporter(applied);
+    const resolvers: Array<() => void> = [];
+    registerRuntimeDataHandler(
+      "captions",
+      () => new Promise<void>((resolve) => resolvers.push(resolve)),
+    );
+
+    // The host mints id 1 and waits on it; the composition then calls the two-argument
+    // public form, which mints an id of its own.
+    setRuntimeData("captions", "first", 1);
+    setRuntimeData("captions", "latest");
+    resolvers[1]?.();
+    await vi.waitFor(() => expect(applied).toHaveBeenCalledTimes(1));
+
+    const [, reportedId] = applied.mock.calls[0] ?? [];
+    expect(reportedId).not.toBe(1);
+  });
 });

packages/core/src/runtime/runtimeData.ts

@@ -28,7 +28,10 @@ function nextGeneration(channel: string): number {
 function resolveRequestId(requestId: number | undefined): number {
   if (typeof requestId === "number" && Number.isSafeInteger(requestId) && requestId > 0)
     return requestId;
-  localRequestId += 1;
+  // Guest-local ids count down so they can never collide with a host id, which is
+  // required above to be positive. A shared id space lets a composition-side call
+  // report `applied` under a host request's id while that host payload is still in flight.
+  localRequestId -= 1;
   return localRequestId;
 }
 

packages/core/src/runtime/window.d.ts

@@ -35,7 +35,7 @@ declare global {
         channel: string,
         handler: (payload: unknown) => void,
       ) => () => void;
-      setRuntimeData?: (channel: string, payload: unknown) => void;
+      setRuntimeData?: (channel: string, payload: unknown, requestId?: number) => void;
       clearRuntimeData?: (channel: string) => void;
       [key: string]: unknown;
     };