fix(muse): list background children under their turn item's native id

packages/provider-muse/src/server/adapter.test.ts

@@ -1704,6 +1704,59 @@ describe("MuseAdapterV2", () => {
     }).pipe(Effect.scoped, Effect.provide(testLayer)),
   );
 
+  it.effect("lists a running subagent under its turn item's native id as Muse reveals it", () =>
+    Effect.gen(function* () {
+      const fake = yield* makeFakeMuse();
+      const harness = yield* makeHarness(fake);
+      const { nativeId } = yield* startConversation(harness, fake);
+      const revisions = [
+        { revision: 1, status: "inProgress" },
+        { revision: 2, status: "inProgress", subagentId: "" },
+        { revision: 3, status: "inProgress", subagentId: "subagent-1" },
+        {
+          revision: 4,
+          status: "inProgress",
+          subagentId: "subagent-1",
+          childSessionId: "child-session-1",
+        },
+        {
+          revision: 5,
+          status: "completed",
+          subagentId: "subagent-1",
+          childSessionId: "child-session-1",
+        },
+      ];
+      const listed: Array<{ nativeId: string | null | undefined; roster: Array<string> }> = [];
+      for (const fields of revisions) {
+        yield* fake.emit(fields.revision === 1 ? "item/started" : "item/updated", {
+          turnId: nativeId,
+          item: { itemId: "sub-1", kind: "subagent", turnId: nativeId, ...fields },
+        });
+        const item = yield* harness.takeEvent(
+          "turn_item.updated",
+          (event) => event.turnItem.type === "subagent",
+        );
+        const roster = harness.allEvents.findLast(
+          (event) => event.type === "provider_thread.updated",
+        );
+        listed.push({
+          nativeId: item.turnItem.nativeItemRef?.nativeId,
+          roster:
+            roster?.type === "provider_thread.updated"
+              ? (roster.providerThread.pendingBackgroundTasks ?? []).map((task) => task.taskId)
+              : [],
+        });
+      }
+      assert.deepStrictEqual(listed, [
+        { nativeId: "sub-1", roster: ["sub-1"] },
+        { nativeId: "sub-1", roster: ["sub-1"] },
+        { nativeId: "subagent-1", roster: ["subagent-1"] },
+        { nativeId: "child-session-1", roster: ["child-session-1"] },
+        { nativeId: "child-session-1", roster: [] },
+      ]);
+    }).pipe(Effect.scoped, Effect.provide(testLayer)),
+  );
+
   it.effect("keeps a workflow child's first label after later revisions drop it", () =>
     Effect.gen(function* () {
       const fake = yield* makeFakeMuse();

packages/provider-muse/src/server/adapter.ts

@@ -248,6 +248,9 @@ const nativeRef = (nativeId: string) => ({
   nativeId,
   strength: "strong" as const,
 });
+/** The roster lists a child under its turn item's native id, so readers can pair the two. */
+const backgroundTaskId = (item: MuseItem) =>
+  item.kind === "subagent" ? item.childSessionId || item.subagentId || item.itemId : item.itemId;
 const recordSchema = Schema.Record(Schema.String, Schema.Unknown);
 const INFORMATIONAL_NOTIFICATIONS = new Set([
   "session/contextUsage",
@@ -595,9 +598,7 @@ export const makeMuseAdapterV2 = Effect.fn("makeMuseAdapterV2")(function* (
           item.result?.summary ??
           (status === "failed" ? item.failureReason : undefined);
         const result = resultText ?? null;
-        const nativeTaskRef = item.childSessionId
-          ? nativeRef(item.childSessionId)
-          : nativeRef(item.subagentId ?? item.itemId);
+        const nativeTaskRef = nativeRef(backgroundTaskId(item));
         const subagent: OrchestrationV2Subagent = {
           id: base.nodeId,
           threadId: base.threadId,
@@ -675,7 +676,7 @@ export const makeMuseAdapterV2 = Effect.fn("makeMuseAdapterV2")(function* (
             const description = item?.objective ?? item?.entryId ?? item?.fallbackText;
             return [
               {
-                taskId: itemId,
+                taskId: item ? backgroundTaskId(item) : itemId,
                 kind:
                   item?.kind === "subagent" ? ("subagent" as const) : ("background_task" as const),
                 ...(description ? { description } : {}),
@@ -714,7 +715,13 @@ export const makeMuseAdapterV2 = Effect.fn("makeMuseAdapterV2")(function* (
                     ? "cancelled"
                     : "failed",
             });
-          if (wasRunning !== observedChildren.has(item.itemId)) yield* syncBackground();
+          const running = observedChildren.has(item.itemId);
+          // Muse reveals a subagent's ids over several revisions, so a running child is
+          // relisted whenever the id its turn item carries moves.
+          const listed = thread?.pendingBackgroundTasks?.some(
+            (task) => task.taskId === backgroundTaskId(item),
+          );
+          if (wasRunning !== running || (running && !listed)) yield* syncBackground();
         }
         const streaming = status === "running";
         const base = {