diff --git a/src/index.ts b/src/index.ts
index db3514e..2a9553e 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -105,7 +105,7 @@ export class AwsAgentCoreAdapter implements BackendAdapter {
     }
 
     const runtimeArn = this.requiredRuntimeArn();
-    const runtimeSessionId = createAgentCoreSessionId();
+    const runtimeSessionId = createAgentCoreSessionId(request.task.id);
     const timestamp = nowIso();
     const session: SessionRecord = {
       id: createId("session"),
@@ -149,7 +149,7 @@ export class AwsAgentCoreAdapter implements BackendAdapter {
   }
 
   async cancel(taskId: string): Promise<CancelResult> {
-    const session = this.sessions.get(taskId);
+    const session = this.sessions.get(taskId) ?? this.fallbackSession(taskId);
     if (!session) {
       return { status: "not_found" };
     }
@@ -215,7 +215,7 @@ export class AwsAgentCoreAdapter implements BackendAdapter {
     } as any));
     await this.waitForEndpoint(agentRuntimeId, endpointName);
 
-    const runtimeSessionId = createAgentCoreSessionId();
+    const runtimeSessionId = createAgentCoreSessionId(request.task.id);
     const timestamp = nowIso();
     const runtime: RuntimeRecord = {
       id: createId("runtime"),
@@ -320,6 +320,15 @@ export class AwsAgentCoreAdapter implements BackendAdapter {
     return this.config.runtimeArn;
   }
 
+  private fallbackSession(taskId: string): { runtimeSessionId: string; runtimeArn: string; qualifier?: string; target?: RuntimeTarget } | undefined {
+    if (!this.config.runtimeArn) return undefined;
+    return {
+      runtimeSessionId: createAgentCoreSessionId(taskId),
+      runtimeArn: this.config.runtimeArn,
+      qualifier: this.config.qualifier
+    };
+  }
+
   private async waitForEndpoint(agentRuntimeId: string, endpointName: string): Promise<void> {
     for (let attempt = 0; attempt < 60; attempt += 1) {
       const endpoint: any = await this.clients.control.send(new GetAgentRuntimeEndpointCommand({ agentRuntimeId, endpointName }));
@@ -351,8 +360,8 @@ export class AwsAgentCoreAdapter implements BackendAdapter {
   }
 }
 
-function createAgentCoreSessionId(): string {
-  return createId("agentcore_session");
+function createAgentCoreSessionId(taskId: string): string {
+  return `ad-${createHash("sha256").update(taskId).digest("hex").slice(0, 32)}`;
 }
 
 function stringDetail(details: Record<string, unknown>, key: string): string | undefined {
diff --git a/test/adapter.test.ts b/test/adapter.test.ts
index 8783454..9c9a7a9 100644
--- a/test/adapter.test.ts
+++ b/test/adapter.test.ts
@@ -199,10 +199,34 @@ describe("AwsAgentCoreAdapter", () => {
     const request = createRequest("agent.run", "session");
     const target = (await adapter.resolveTarget(request)).target;
     const task = createTask(request);
-    await adapter.provision({ dispatch: request, task, target });
+    const provisioned = await adapter.provision({ dispatch: request, task, target });
 
     await expect(adapter.cancel(task.id)).resolves.toMatchObject({ status: "cancelled" });
     expect(data.commands.map((command) => command.constructor.name)).toContain("StopRuntimeSessionCommand");
+    expect(data.commands.find((command) => command.constructor.name === "StopRuntimeSessionCommand").input.runtimeSessionId)
+      .toBe(provisioned.session?.providerRefs.runtimeSessionId);
+  });
+
+  it("can cancel a session-mode task after adapter restart", async () => {
+    const firstData = new FakeDataClient();
+    const firstAdapter = createAdapter(firstData);
+    const request = createRequest("agent.run", "session");
+    const target = (await firstAdapter.resolveTarget(request)).target;
+    const task = createTask(request);
+    const provisioned = await firstAdapter.provision({ dispatch: request, task, target });
+
+    const restartedData = new FakeDataClient();
+    const restartedAdapter = createAdapter(restartedData);
+    await expect(restartedAdapter.cancel(task.id)).resolves.toMatchObject({
+      status: "cancelled",
+      providerRefs: { runtimeSessionId: provisioned.session?.providerRefs.runtimeSessionId }
+    });
+
+    const stop = restartedData.commands.find((command) => command.constructor.name === "StopRuntimeSessionCommand");
+    expect(stop.input).toMatchObject({
+      agentRuntimeArn: "arn:aws:bedrock-agentcore:us-west-2:123456789012:agent/00000000-0000-0000-0000-000000000000:1",
+      runtimeSessionId: provisioned.session?.providerRefs.runtimeSessionId
+    });
   });
 });