diff --git a/packages/workflow/workflow-workerthread/README.md b/packages/workflow/workflow-workerthread/README.md
index 25c79ad09c..dc8859d351 100644
--- a/packages/workflow/workflow-workerthread/README.md
+++ b/packages/workflow/workflow-workerthread/README.md
@@ -32,7 +32,7 @@ Values LEAVING the script (hook options/schemas, the script's return) are materi
 
 Per-run limits: a concurrency semaphore (`maxConcurrentAgents`), a total-`agent()` cap (`maxTotalAgents`), and a per-call item cap (`maxItemsPerCall`), all config. `cancel()` posts the cancel to the worker (its hooks start throwing `CANCELLED`; the script dies at its next await) and cancels every host-side child NOW on **both seam channels** — the shared request signal aborts AND each registered child's explicit `cancel()` is called host-side, because the seam leaves a provider free to honor either channel and a worker wedged in a synchronous spin could not relay its own per-child cancel RPCs (those later land as idempotent no-ops). The grace then arms: a run still unsettled `disposeGraceMs` later force-settles `cancelled` and the worker is **terminated**. A cancellation that lands before the body runs (the ready→go handshake) reports `cancelled` without executing anything; a worker `result` racing an in-flight host cancellation reports `cancelled` too (first-wins settlement — the seam-visible result had not settled when cancellation was requested); post-cancel `phase`/`log` narration is suppressed host-side, while cancelled children still deliver their paired `agent-end`.
 
-A worker that dies unexpectedly (an OOM, a script reaching `process.exit` through the documented vm escape) settles the run `stopReason: 'error'` with the exit diagnostics — or `'cancelled'` when a cancel was in flight — and the host-side child registry is what winds every surviving child down. `dispose()` = cancel + bounded wait (result, then child-registry quiescence, capped by the grace) + unconditional `worker.terminate()`: the thread never outlives its run. Once a run settles, stray children a script fired without awaiting are cancelled too, and `dispose()` waits for their disposal (bounded by the grace) before returning.
+A worker that dies unexpectedly (an OOM, a script reaching `process.exit` through the documented vm escape) settles the run `stopReason: 'error'` with the exit diagnostics — or `'cancelled'` when a cancel was in flight — and the host-side child registry is what winds every surviving child down. `dispose()` = cancel + immediate host-driven disposal of every registered child (a wedged worker can relay no dispose RPC, so child teardown overlaps the grace instead of starting after it; the worker's own dispose RPCs join the same per-child disposal) + bounded wait (result, then child-registry quiescence, capped by the grace) + unconditional `worker.terminate()`: the thread never outlives its run. Once a run settles, stray children a script fired without awaiting are cancelled too, and `dispose()` waits for their disposal (bounded by the grace) before returning.
 
 **Engine-specific limitations**: worker startup is paid per run; on a termination path `agentsStarted` reports the HOST-observed count (accepted `child-start`s — calls still queued worker-side for a concurrency slot are unknowable then); and a returned promise or thenable resolves per JavaScript semantics BEFORE materialization — that is what makes an un-awaited `return agent('x')` work — with the value-boundary guard applying to the resolution.
 
diff --git a/packages/workflow/workflow-workerthread/src/host.ts b/packages/workflow/workflow-workerthread/src/host.ts
index 9d98d00933..c512c15dee 100644
--- a/packages/workflow/workflow-workerthread/src/host.ts
+++ b/packages/workflow/workflow-workerthread/src/host.ts
@@ -15,9 +15,14 @@
  * terminated — the real kill an in-process engine could not perform).
  *
  * Children live in a host-side registry (callId → run): the worker drives
- * their disposal by RPC on the graceful path, and the registry is what lets
- * the host abort and dispose every survivor when the worker dies or is
- * terminated mid-flight. On a termination path `agentsStarted` reports the
+ * their disposal by RPC on the graceful path, `dispose()` host-drives every
+ * registered child's disposal immediately (a wedged worker can relay no
+ * dispose RPC, and child teardown must overlap the grace, not start after
+ * it), and the registry is what lets the host abort and dispose every
+ * survivor when the worker dies or is terminated mid-flight. The three
+ * paths share ONE disposal per child (memoized by callId; the seam's
+ * dispose() is idempotent anyway, the memo keeps the bookkeeping and the
+ * containment warn single). On a termination path `agentsStarted` reports the
  * HOST-observed count (accepted `child-start` messages) — `agent()` calls
  * still queued worker-side for a concurrency slot are unknowable then; the
  * worker's own count rides the result message on every graceful path.
@@ -85,6 +90,8 @@ export class WorkerRun implements WorkflowRun {
   private hostStarted = 0
   /** Live children by callId; an entry leaves ONLY after its dispose settles (quiescence = empty). */
   private readonly children = new Map<number, SubagentRun>()
+  /** In-flight child disposals by callId — the memo that gives every path (worker RPC, dispose(), reap) ONE shared disposal per child. */
+  private readonly childDisposals = new Map<number, Promise<void>>()
   private readonly quiescenceWaiters: (() => void)[] = []
   /** The per-run abort fanout every child start request carries. */
   private readonly controller = new AbortController()
@@ -156,17 +163,24 @@ export class WorkerRun implements WorkflowRun {
   }
 
   /**
-   * Cancel + bounded settle + termination. Waits (at most the grace) for the
-   * result and child quiescence, then terminates the worker unconditionally
-   * — the thread never outlives its run — and reaps whatever children
-   * remain (their disposal is contained, not awaited past the grace, the
-   * same abandonment the seam documents for a slow-disposing child).
-   * Idempotent; safe on every path.
+   * Cancel + bounded settle + termination. Host-drives every registered
+   * child's disposal IMMEDIATELY — a wedged worker can relay no dispose RPC,
+   * and deferring child teardown to the post-terminate reap would spend the
+   * whole grace waiting for a quiescence that cannot start, then return with
+   * the disposals still in flight — so child disposal overlaps the same
+   * grace the worker gets to settle (the worker's own dispose RPCs join the
+   * shared per-child disposal). Waits (at most the grace) for the result and
+   * child quiescence, then terminates the worker unconditionally — the
+   * thread never outlives its run — and reaps whatever children remain
+   * (their disposal is contained, not awaited past the grace, the same
+   * abandonment the seam documents for a slow-disposing child). Idempotent;
+   * safe on every path.
    * @returns resolves when the run's resources are released or abandoned.
    */
   dispose(): Promise<void> {
     this.disposed ??= (async () => {
       this.cancel('workflow disposed')
+      for (const [callId, run] of [...this.children]) void this.disposeChild(callId, run)
       await Promise.race([
         (async () => {
           await this.result
@@ -278,31 +292,47 @@ export class WorkerRun implements WorkflowRun {
 
   private onChildDispose(callId: number): void {
     const run = this.children.get(callId)
-    /* v8 ignore next 5 -- dispose RPC for an already-reaped child: only a worker-death race can produce it, not orderable in-process */
     if (run === undefined) {
-      // Already reaped — the ack is still owed (the worker-side wrapper awaits it).
+      // Already disposed host-side (a dispose() drive or a death reap beat
+      // the RPC) — the ack is still owed (the worker-side wrapper awaits it).
       this.post(HostToWorkerType.ChildDisposed, { callId })
       return
     }
-    void run.dispose().then(
-      () => {
-        this.finishChild(callId)
-        this.post(HostToWorkerType.ChildDisposed, { callId })
-      },
-      (error: unknown) => {
-        // The subagent seam's dispose() is not supposed to reject; a backend
-        // that does anyway must not wedge the script's finally (which awaits
-        // the ack) — ack and move on.
-        this.ctx.logger.warn(`workflow-workerthread: child dispose failed: ${renderThrown(error)}`)
-        this.finishChild(callId)
-        this.post(HostToWorkerType.ChildDisposed, { callId })
-      },
-    )
+    // disposeChild never rejects (containment is inside), so the ack always follows.
+    void this.disposeChild(callId, run).then(() => { this.post(HostToWorkerType.ChildDisposed, { callId }) })
   }
 
-  /** Drop a child from the registry, releasing quiescence waiters at zero. */
+  /**
+   * Start (or join) one registered child's disposal; the registry entry
+   * leaves when it settles. Memoized per callId: the worker's dispose RPC,
+   * the dispose() host drive, and the reap can all land on the same child —
+   * the child's `dispose()` runs once and every caller awaits that one
+   * settlement. A rejection is contained (the subagent seam's dispose() is
+   * not supposed to reject, but a backend that does anyway must not break
+   * quiescence): logged, and the child still leaves the registry.
+   * @param callId - the child's registry key.
+   * @param run - the registered child (the caller looked it up).
+   * @returns resolves when the disposal settled either way; never rejects.
+   */
+  private disposeChild(callId: number, run: SubagentRun): Promise<void> {
+    let disposal = this.childDisposals.get(callId)
+    if (disposal === undefined) {
+      disposal = run.dispose().then(
+        () => { this.finishChild(callId) },
+        (error: unknown) => {
+          this.ctx.logger.warn(`workflow-workerthread: child dispose failed: ${renderThrown(error)}`)
+          this.finishChild(callId)
+        },
+      )
+      this.childDisposals.set(callId, disposal)
+    }
+    return disposal
+  }
+
+  /** Drop a child from the registry (and its disposal memo), releasing quiescence waiters at zero. */
   private finishChild(callId: number): void {
     this.children.delete(callId)
+    this.childDisposals.delete(callId)
     if (this.children.size === 0) {
       for (const waiter of this.quiescenceWaiters.splice(0)) waiter()
     }
@@ -319,13 +349,7 @@ export class WorkerRun implements WorkflowRun {
     this.controller.abort(this.cancelReason ?? reason)
     for (const [callId, run] of [...this.children]) {
       run.cancel(this.cancelReason ?? reason)
-      void run.dispose().then(
-        () => { this.finishChild(callId) },
-        (error: unknown) => {
-          this.ctx.logger.warn(`workflow-workerthread: child dispose failed during reap: ${renderThrown(error)}`)
-          this.finishChild(callId)
-        },
-      )
+      void this.disposeChild(callId, run)
     }
   }
 
diff --git a/packages/workflow/workflow-workerthread/tests/workflow-workerthread.spec.ts b/packages/workflow/workflow-workerthread/tests/workflow-workerthread.spec.ts
index 378dd6ecf6..c1c26dcf0f 100644
--- a/packages/workflow/workflow-workerthread/tests/workflow-workerthread.spec.ts
+++ b/packages/workflow/workflow-workerthread/tests/workflow-workerthread.spec.ts
@@ -23,6 +23,7 @@ interface ControlledRun {
   settle(result: SubagentResult): void
   cancelled: string | undefined
   disposed: boolean
+  disposeCalls: number
 }
 
 /**
@@ -45,7 +46,7 @@ class StubProvider implements SubagentProvider {
   start(request: SubagentStartRequest): SubagentRun {
     let settle!: (result: SubagentResult) => void
     const result = new Promise<SubagentResult>((resolve) => { settle = resolve })
-    const controlled: ControlledRun = { request, settle, cancelled: undefined, disposed: false }
+    const controlled: ControlledRun = { request, settle, cancelled: undefined, disposed: false, disposeCalls: 0 }
     this.runs.push(controlled)
     const index = this.runs.length - 1
     request.signal?.addEventListener('abort', () => { settle({ output: [], stopReason: 'aborted' }) }, { once: true })
@@ -61,6 +62,7 @@ class StubProvider implements SubagentProvider {
         settle({ output: [], stopReason: 'aborted' })
       },
       dispose: () => {
+        controlled.disposeCalls += 1
         if (this.disposeDelayMs === 0) {
           controlled.disposed = true
           return Promise.resolve()
@@ -537,6 +539,64 @@ describe('dsh-workflow-workerthread', () => {
       expect(result.stopReason).toBe('cancelled')
       await handle.dispose()
     }, 15_000)
+
+    it('dispose() on a wedged worker host-drives child disposal inside the grace: it returns with the children DISPOSED, not with their teardown still in flight', async () => {
+      const { ctx, parent, provider } = await setup({
+        manual: true,
+        disposeDelayMs: 40,
+        config: { provider: 'stub', maxConcurrentAgents: 8, disposeGraceMs: 400 },
+      })
+      const handle = ctx.workflows.start({
+        // Same shape as the wedged-cancel test above: the child's start RPC
+        // reaches the host, then the script seizes its worker's loop, so the
+        // worker can relay NO dispose RPC — the host's own dispose() drive is
+        // the only thing that can start (and finish) this child's disposal
+        // before the grace runs out.
+        ...scripted(`
+          agent('wedged child')
+          for (let i = 0; i < 20; i++) await null
+          const end = Date.now() + 1500
+          while (Date.now() < end) {}
+          return 'raced'
+        `),
+        parent,
+      })
+      await vi.waitFor(() => { expect(provider.runs.length).toBe(1) })
+      const before = Date.now()
+      await handle.dispose()
+      // Bounded by the grace (plus the terminate), never by the 1.5s spin.
+      expect(Date.now() - before).toBeLessThan(1200)
+      // Not a waitFor: dispose() resolving IS the quiescence claim — the slow
+      // child disposal must be complete, not merely started (before the
+      // host-driven drive, disposal only STARTED at the post-terminate reap,
+      // so dispose() returned with it still in flight).
+      expect(provider.runs[0]!.disposed).toBe(true)
+      const result = await handle.result
+      expect(result.stopReason).toBe('cancelled')
+    }, 15_000)
+
+    it('a live child disposed by the dispose() drive is disposed ONCE, and the worker\'s late dispose RPC still gets its ack (the script settles, not the grace)', async () => {
+      const { ctx, parent, provider } = await setup({ manual: true })
+      const handle = ctx.workflows.start({
+        ...scripted(`
+          await agent('long child')
+          return 'unreachable'
+        `),
+        parent,
+      })
+      await vi.waitFor(() => { expect(provider.runs.length).toBe(1) })
+      const handleDispose = handle.dispose()
+      const result = await handle.result
+      // The script itself settled (the wrapper's own dispose RPC found the
+      // child already reaped host-side and was acked) — a missing ack would
+      // wedge the wrapper's finally until the 5s default grace force-settle.
+      expect(result.stopReason).toBe('cancelled')
+      expect(result.error).toContain('workflow disposed')
+      await handleDispose
+      expect(provider.runs[0]!.disposed).toBe(true)
+      // The memo: the host drive and the worker's RPC share one disposal.
+      expect(provider.runs[0]!.disposeCalls).toBe(1)
+    })
   })
 
   describe('worker death', () => {