diff --git a/apps/server/src/orchestration-v2/Adapters/AcpAdapterV2.test.ts b/apps/server/src/orchestration-v2/Adapters/AcpAdapterV2.test.ts
index 28c241ba82f8..4981140ad992 100644
--- a/apps/server/src/orchestration-v2/Adapters/AcpAdapterV2.test.ts
+++ b/apps/server/src/orchestration-v2/Adapters/AcpAdapterV2.test.ts
@@ -5834,12 +5834,17 @@ describe("AcpAdapterV2", () => {
         );
         const protocolEvents = yield* Queue.bounded<EffectAcpProtocol.AcpProtocolLogEvent>(256);
         const continuationRequests: Array<ProviderContinuationRequest> = [];
+        const promptSettled = yield* Deferred.make<void>();
         const instanceId = ProviderInstanceId.make("acp-test");
         const childSessionId = "mock-child-session-post-settle";
         let subagentPhase: "spawn" | "complete" = "spawn";
         type RuntimeService = AcpSessionRuntime.AcpSessionRuntime["Service"];
         let sessionUpdateHandler: Parameters<RuntimeService["handleSessionUpdate"]>[0] | undefined;
         const adapter = makeAcpAdapterV2({
+          testHooks: {
+            afterPromptSettledWithBackgroundWork: () =>
+              Deferred.succeed(promptSettled, undefined).pipe(Effect.asVoid),
+          },
           crypto: yield* Crypto.Crypto,
           instanceId,
           flavor: {
@@ -5929,28 +5934,13 @@ describe("AcpAdapterV2", () => {
         yield* runtime.startTurn(
           makeTurnInput({ threadId, providerThread, instanceId, runtimePolicy, now }),
         );
-        yield* Stream.fromQueue(protocolEvents).pipe(
-          Stream.filter(
-            (event) =>
-              event.direction === "incoming" &&
-              event.stage === "raw" &&
-              typeof event.payload === "string" &&
-              event.payload.includes('"stopReason"'),
-          ),
-          Stream.runHead,
-        );
-        yield* Effect.yieldNow;
-        yield* Effect.yieldNow;
+        yield* Deferred.await(promptSettled);
 
         const firstProviderTurnId = idAllocator.derive.providerTurn({
           driver: ACP_TEST_DRIVER,
           nativeTurnId: acpScopedNativeId(instanceId, "mock-session-1:turn:1"),
         });
-        const interruptFiber = yield* runtime
-          .interruptTurn({ providerThread, providerTurnId: firstProviderTurnId })
-          .pipe(Effect.forkScoped);
-        yield* TestClock.adjust("10 seconds");
-        yield* Fiber.join(interruptFiber);
+        yield* runtime.interruptTurn({ providerThread, providerTurnId: firstProviderTurnId });
 
         let firstTerminalStatus: string | null = null;
         while (firstTerminalStatus === null) {
@@ -7006,12 +6996,17 @@ describe("AcpAdapterV2", () => {
       );
       const protocolEvents = yield* Queue.bounded<EffectAcpProtocol.AcpProtocolLogEvent>(256);
       const continuationRequests: Array<ProviderContinuationRequest> = [];
+      const promptSettled = yield* Deferred.make<void>();
       const instanceId = ProviderInstanceId.make("acp-test");
       const childSessionId = "019f5470-bf92-7a90-afb3-5a6cea5b34a3";
       let subagentPhase: "spawn" | "complete" = "spawn";
       type RuntimeService = AcpSessionRuntime.AcpSessionRuntime["Service"];
       let sessionUpdateHandler: Parameters<RuntimeService["handleSessionUpdate"]>[0] | undefined;
       const adapter = makeAcpAdapterV2({
+        testHooks: {
+          afterPromptSettledWithBackgroundWork: () =>
+            Deferred.succeed(promptSettled, undefined).pipe(Effect.asVoid),
+        },
         crypto: yield* Crypto.Crypto,
         instanceId,
         flavor: {
@@ -7110,28 +7105,13 @@ describe("AcpAdapterV2", () => {
       yield* runtime.startTurn(
         makeTurnInput({ threadId, providerThread, instanceId, runtimePolicy, now }),
       );
-      yield* Stream.fromQueue(protocolEvents).pipe(
-        Stream.filter(
-          (event) =>
-            event.direction === "incoming" &&
-            event.stage === "raw" &&
-            typeof event.payload === "string" &&
-            event.payload.includes('"stopReason"'),
-        ),
-        Stream.runHead,
-      );
-      yield* Effect.yieldNow;
-      yield* Effect.yieldNow;
+      yield* Deferred.await(promptSettled);
 
       const firstProviderTurnId = idAllocator.derive.providerTurn({
         driver: ACP_TEST_DRIVER,
         nativeTurnId: acpScopedNativeId(instanceId, "mock-session-1:turn:1"),
       });
-      const interruptFiber = yield* runtime
-        .interruptTurn({ providerThread, providerTurnId: firstProviderTurnId })
-        .pipe(Effect.forkScoped);
-      yield* TestClock.adjust("10 seconds");
-      yield* Fiber.join(interruptFiber);
+      yield* runtime.interruptTurn({ providerThread, providerTurnId: firstProviderTurnId });
 
       let firstTerminalStatus: string | null = null;
       while (firstTerminalStatus === null) {
@@ -8539,7 +8519,12 @@ describe("AcpAdapterV2", () => {
         const authoritativeSubagentText = "authoritative subagent carryover text";
         type RuntimeService = AcpSessionRuntime.AcpSessionRuntime["Service"];
         let sessionUpdateHandler: Parameters<RuntimeService["handleSessionUpdate"]>[0] | undefined;
+        const promptSettled = yield* Deferred.make<void>();
         const adapter = makeAcpAdapterV2({
+          testHooks: {
+            afterPromptSettledWithBackgroundWork: () =>
+              Deferred.succeed(promptSettled, undefined).pipe(Effect.asVoid),
+          },
           crypto: yield* Crypto.Crypto,
           instanceId,
           flavor: {
@@ -8629,18 +8614,7 @@ describe("AcpAdapterV2", () => {
         yield* runtime.startTurn(
           makeTurnInput({ threadId, providerThread, instanceId, runtimePolicy, now }),
         );
-        yield* Stream.fromQueue(protocolEvents).pipe(
-          Stream.filter(
-            (event) =>
-              event.direction === "incoming" &&
-              event.stage === "raw" &&
-              typeof event.payload === "string" &&
-              event.payload.includes('"stopReason"'),
-          ),
-          Stream.runHead,
-        );
-        yield* Effect.yieldNow;
-        yield* Effect.yieldNow;
+        yield* Deferred.await(promptSettled);
 
         // Project an authoritative v2 assistant-message upsert onto the carryover
         // subagent while the deferred turn is still active.
diff --git a/apps/server/src/orchestration-v2/Adapters/AcpAdapterV2.ts b/apps/server/src/orchestration-v2/Adapters/AcpAdapterV2.ts
index d53a5f33039f..805b693b6e78 100644
--- a/apps/server/src/orchestration-v2/Adapters/AcpAdapterV2.ts
+++ b/apps/server/src/orchestration-v2/Adapters/AcpAdapterV2.ts
@@ -516,6 +516,7 @@ export interface AcpAdapterV2Options {
      * by exactly that on this receipt.
      */
     readonly onDeferredFinalizeScheduled?: (debounce: Duration.Input) => Effect.Effect<void>;
+    readonly afterPromptSettledWithBackgroundWork?: () => Effect.Effect<void>;
     readonly afterNativeResponseTransportClosed?: () => Effect.Effect<void>;
     readonly afterHardTeardownTransportDrained?: () => Effect.Effect<void>;
     readonly beforeNativeResponseAdmissionCheck?: (
@@ -6935,6 +6936,9 @@ export function makeAcpAdapterV2(options: AcpAdapterV2Options): ProviderAdapterV
                       // The agent finished this prompt's reply. Background work
                       // holds the run open, not the text it already sent.
                       yield* closeTextStreams(context);
+                      yield* (
+                        options.testHooks?.afterPromptSettledWithBackgroundWork?.() ?? Effect.void
+                      );
                       return;
                     }
                     yield* finalizeTurn(context, status);