diff --git a/agent-runtime/server/agent-event-store.ts b/agent-runtime/server/agent-event-store.ts
index 2dc0e71d..bfd69533 100644
--- a/agent-runtime/server/agent-event-store.ts
+++ b/agent-runtime/server/agent-event-store.ts
@@ -43,9 +43,11 @@ export interface AgentEventPayloads {
     callStack: string[]
     depth: number
     input: string
+    parentAgentId?: string | null
     parentRunId?: string | null
     parentToolCallId?: string | null
     parentToolId?: string | null
+    reportBackToParent?: boolean
     streamToken: string
   }
 }
diff --git a/agent-runtime/server/session-events.ts b/agent-runtime/server/session-events.ts
index c737ac1c..d7064128 100644
--- a/agent-runtime/server/session-events.ts
+++ b/agent-runtime/server/session-events.ts
@@ -110,10 +110,12 @@ export async function dispatchInvocation(input: {
   childAgentId: string
   childUserId: string
   parentUserId: string
+  parentAgentId: string
   parentRunId: string | null
   parentToolId: string
   parentToolCallId?: string | null
   instruction: string
+  reportBackToParent?: boolean
   streamToken: string
   callStack: string[]
   depth: number
@@ -150,9 +152,11 @@ export async function dispatchInvocation(input: {
       callStack: input.callStack,
       depth: input.depth,
       input: input.instruction,
+      parentAgentId: input.parentAgentId,
       parentRunId: input.parentRunId,
       parentToolCallId: input.parentToolCallId ?? null,
       parentToolId: input.parentToolId,
+      reportBackToParent: input.reportBackToParent ?? false,
       streamToken: input.streamToken,
     },
     source: 'invocation',
diff --git a/agent-runtime/workflows/events/workflow.ts b/agent-runtime/workflows/events/workflow.ts
index 4027727b..29c8311b 100644
--- a/agent-runtime/workflows/events/workflow.ts
+++ b/agent-runtime/workflows/events/workflow.ts
@@ -137,9 +137,11 @@ async function dispatchAgentEvent(event: WorkflowAgentEvent): Promise<void> {
         callStack: payload.callStack,
         depth: payload.depth,
         input: payload.input,
+        parentAgentId: payload.parentAgentId ?? null,
         parentRunId: payload.parentRunId ?? null,
         parentToolCallId: payload.parentToolCallId ?? null,
         parentToolId: payload.parentToolId ?? null,
+        reportBackToParent: payload.reportBackToParent ?? false,
         parentStream: null,
         replyToken: replyNamespaceForEvent(event.id),
         streamToken: payload.streamToken,
diff --git a/agent-runtime/workflows/session/handlers/handle-invocation.ts b/agent-runtime/workflows/session/handlers/handle-invocation.ts
index 5b480dfe..4105ac3c 100644
--- a/agent-runtime/workflows/session/handlers/handle-invocation.ts
+++ b/agent-runtime/workflows/session/handlers/handle-invocation.ts
@@ -29,10 +29,12 @@ export async function handleInvocation(input: {
   agentId: string
   input: string
   streamToken: string
+  parentAgentId?: string | null
   parentRunId?: string | null
   parentToolId?: string | null
   parentToolCallId?: string | null
   parentStream?: WritableStream<UIMessageChunk> | null
+  reportBackToParent?: boolean
   replyToken?: string | null
   callStack: string[]
   depth: number
@@ -40,11 +42,13 @@ export async function handleInvocation(input: {
   const {
     agentId,
     input: instruction,
+    parentAgentId,
     streamToken,
     parentRunId,
     parentToolId,
     parentToolCallId,
     parentStream,
+    reportBackToParent,
     replyToken,
     callStack,
     depth,
@@ -151,6 +155,13 @@ export async function handleInvocation(input: {
     })
     await finishInvocationStreams(streamNamespaces)
     await forwardPromise
+    await maybeReportBackToParent({
+      childAgentId: agentId,
+      childName: built.meta.name,
+      finalText: extractFinalAssistantText(result.uiMessages),
+      parentAgentId: parentAgentId ?? null,
+      reportBackToParent: reportBackToParent ?? false,
+    })
   } catch (err) {
     await failInvocation({
       err,
@@ -163,6 +174,72 @@ export async function handleInvocation(input: {
   }
 }
 
+async function maybeReportBackToParent(input: {
+  childAgentId: string
+  childName: string
+  finalText: string | null
+  parentAgentId: string | null
+  reportBackToParent: boolean
+}): Promise<void> {
+  if (!input.reportBackToParent || !input.parentAgentId || !input.finalText) {
+    return
+  }
+  const { dispatchInvocation } = await import(
+    '@/agent-runtime/server/session-events'
+  )
+  await dispatchInvocation({
+    childAgentId: input.parentAgentId,
+    childUserId: await resolveAgentUserId(input.parentAgentId),
+    parentAgentId: input.childAgentId,
+    parentUserId: await resolveAgentUserId(input.parentAgentId),
+    parentRunId: null,
+    parentToolId: 'sub_agent_report_back',
+    instruction: [
+      `Sub-agent "${input.childName}" completed delegated async work.`,
+      `Result: ${input.finalText}`,
+    ].join('\n'),
+    streamToken: `report_back_${Date.now().toString(36)}`,
+    callStack: [input.parentAgentId],
+    depth: 0,
+  })
+}
+
+async function resolveAgentUserId(agentId: string): Promise<string> {
+  const { db } = await import('@/shared/db')
+  const { agent } = await import('@/shared/db/schema')
+  const { eq } = await import('drizzle-orm')
+  const [row] = await db.select().from(agent).where(eq(agent.id, agentId)).limit(1)
+  if (!row) {
+    throw new Error(`resolveAgentUserId: agent ${agentId} not found`)
+  }
+  return row.userId
+}
+
+function extractFinalAssistantText(
+  messages: readonly UIMessage[] | undefined
+): string | null {
+  if (!messages) {
+    return null
+  }
+  for (let i = messages.length - 1; i >= 0; i--) {
+    const message = messages[i]
+    if (message.role !== 'assistant') {
+      continue
+    }
+    const chunks: string[] = []
+    for (const part of message.parts ?? []) {
+      if (part.type === 'text' && typeof part.text === 'string') {
+        chunks.push(part.text)
+      }
+    }
+    const text = chunks.join('').trim()
+    if (text.length > 0) {
+      return text
+    }
+  }
+  return null
+}
+
 async function finishInvocationStreams(
   namespaces: readonly string[]
 ): Promise<void> {
diff --git a/tools/sub-agents/agent-tool.ts b/tools/sub-agents/agent-tool.ts
index 470082f7..b3beb0ee 100644
--- a/tools/sub-agents/agent-tool.ts
+++ b/tools/sub-agents/agent-tool.ts
@@ -46,8 +46,20 @@ export function buildAgentTool(handle: AgentToolHandle) {
             'text returned as the tool result.',
           ].join(' ')
         ),
+      waitForCompletion: z
+        .boolean()
+        .optional()
+        .describe(
+          [
+            'Whether to wait for the sub-agent final answer.',
+            'Set to false for long-running delegated work that does not',
+            'block your next step; in that case this tool returns immediately',
+            'after the child run is queued.',
+          ].join(' ')
+        ),
     }),
-    async execute({ instruction }, { toolCallId }) {
+    async execute({ instruction, waitForCompletion }, { toolCallId }) {
+      const shouldWait = waitForCompletion ?? true
       const streamToken = newInvocationStreamToken()
       const messages: AgentChatMessage[] = []
       await emitPreliminarySubAgentOutput({
@@ -64,9 +76,18 @@ export function buildAgentTool(handle: AgentToolHandle) {
         const { sessionRunId } = await dispatchSubAgentInvocation({
           handle,
           instruction,
+          reportBackToParent: !shouldWait,
           streamToken,
           toolCallId,
         })
+        if (!shouldWait) {
+          return subAgentOutput({
+            finalText: `Sub-agent "${handle.childName}" started asynchronously (run: ${sessionRunId}). Continue your current work and use this run id to inspect completion later.`,
+            handle,
+            messages,
+            status: 'completed',
+          })
+        }
         const { error, messages: childMessages } =
           await collectSubAgentMessages({
             progress: {
@@ -132,22 +153,26 @@ function modelOutputText(output: unknown): string {
 async function dispatchSubAgentInvocation(input: {
   handle: AgentToolHandle
   instruction: string
+  reportBackToParent: boolean
   streamToken: string
   toolCallId: string
 }): Promise<{ sessionRunId: string }> {
   'use step'
-  const { handle, instruction, streamToken, toolCallId } = input
+  const { handle, instruction, reportBackToParent, streamToken, toolCallId } =
+    input
   const { dispatchInvocation } = await import(
     '@/agent-runtime/server/session-events'
   )
   return await dispatchInvocation({
     childAgentId: handle.childAgentId,
     childUserId: handle.childUserId,
+    parentAgentId: handle.parentAgentId,
     parentUserId: handle.parentUserId,
     parentRunId: handle.parentRunId,
     parentToolId: handle.parentToolId,
     parentToolCallId: toolCallId,
     instruction,
+    reportBackToParent,
     streamToken,
     callStack: [...handle.parentCallStack, handle.parentAgentId],
     depth: handle.parentDepth + 1,
@@ -210,7 +235,7 @@ function composeDescription(handle: AgentToolHandle): string {
     (summary ? `Capability summary: ${summary} ` : '') +
     'Provide a fully self-contained instruction; the sub-agent does ' +
     'not see your conversation, memory, or files unless you include ' +
-    "them in the instruction. Returns the sub-agent's final text reply."
+    'them in the instruction. By default this tool waits for the sub-agent final text reply, but you can set waitForCompletion=false for long-running work and continue immediately.'
   )
 }