diff --git a/docs/config-catalog.md b/docs/config-catalog.md
index 7921b98f55..dd652c7d45 100644
--- a/docs/config-catalog.md
+++ b/docs/config-catalog.md
@@ -866,7 +866,7 @@ export interface Config {
    * before the parent escalates to a signal.
    */
   disposeEofGraceMs?: number
-  /** POSIX grace period (ms) between `SIGTERM` and `SIGKILL`; unused on Windows. */
+  /** Termination confirmation window (ms), including forced exit on every platform. */
   disposeGraceMs?: number
 }
 
diff --git a/packages/subagent/subagent-acp/README.md b/packages/subagent/subagent-acp/README.md
index 830335bbb5..240b79c2d7 100644
--- a/packages/subagent/subagent-acp/README.md
+++ b/packages/subagent/subagent-acp/README.md
@@ -10,7 +10,7 @@ The returned run id is minted in the parent namespace. The child server's sessio
 
 After publication, the provider sends the prompt and collects streamed `agent_message_chunk` text into `SubagentResult.output`. A prompt/transport failure resolves with `stopReason: 'error'`, or `aborted` when the required request signal or disposal requested cancellation.
 
-`dispose()` is idempotent. It removes the signal listener, requests ACP cancellation when possible, closes stdin, and waits `disposeEofGraceMs`. POSIX then escalates through SIGTERM and `disposeGraceMs` before SIGKILL; Windows force-terminates directly because Node maps both signals to `TerminateProcess`. Disposal resolves only after child exit. Every run uses a fresh process; process pooling is not implemented.
+`dispose()` is idempotent. It removes the signal listener, requests ACP cancellation when possible, closes stdin, and waits `disposeEofGraceMs`. POSIX then escalates through SIGTERM and `disposeGraceMs` before SIGKILL; Windows force-terminates directly because Node maps both signals to `TerminateProcess`. After forced termination, every platform waits at most `disposeGraceMs` for exit and rejects on a signal error or missing exit. Every run uses a fresh process; process pooling is not implemented.
 
 ## Capabilities and context
 
@@ -27,7 +27,7 @@ ACP advertises no start-time capabilities because this process cannot enforce th
 | `permission` | `reject` | Auto-answer permission requests by rejecting or choosing the first allow-shaped option. |
 | `env` | `{}` | Explicit child environment layered over a credential-scrubbed parent environment. |
 | `disposeEofGraceMs` | `6000` | Grace after stdin EOF before platform termination. |
-| `disposeGraceMs` | `3000` | POSIX grace after SIGTERM before SIGKILL; unused on Windows. |
+| `disposeGraceMs` | `3000` | Exit-confirmation grace after termination; POSIX also waits this long after SIGTERM before SIGKILL. |
 
 ```yaml
 - id: subagent-acp
diff --git a/packages/subagent/subagent-acp/src/index.ts b/packages/subagent/subagent-acp/src/index.ts
index 697be5b98a..0a761831ea 100644
--- a/packages/subagent/subagent-acp/src/index.ts
+++ b/packages/subagent/subagent-acp/src/index.ts
@@ -46,7 +46,7 @@ export interface Config {
    * before the parent escalates to a signal.
    */
   disposeEofGraceMs?: number
-  /** POSIX grace period (ms) between `SIGTERM` and `SIGKILL`; unused on Windows. */
+  /** Termination confirmation window (ms), including forced exit on every platform. */
   disposeGraceMs?: number
 }
 
diff --git a/packages/subagent/subagent-acp/src/run.ts b/packages/subagent/subagent-acp/src/run.ts
index 9f037a170c..09a6ed81e9 100644
--- a/packages/subagent/subagent-acp/src/run.ts
+++ b/packages/subagent/subagent-acp/src/run.ts
@@ -56,9 +56,9 @@ export interface AcpRunSpec {
    */
   disposeEofGraceMs: number
   /**
-   * POSIX grace period (ms) between `SIGTERM` and `SIGKILL` in
-   * {@link SubagentRun.dispose}; unused on Windows. The plugin fills this from
-   * its `disposeGraceMs` config.
+   * Termination confirmation window (ms) in {@link SubagentRun.dispose}; POSIX applies it after
+   * `SIGTERM` and `SIGKILL`, while Windows applies it after direct forced termination. The plugin
+   * fills this from its `disposeGraceMs` config.
    */
   disposeGraceMs: number
   /**
diff --git a/packages/subagent/subagent-subprocess/README.md b/packages/subagent/subagent-subprocess/README.md
index 4a72f6279b..80be43125e 100644
--- a/packages/subagent/subagent-subprocess/README.md
+++ b/packages/subagent/subagent-subprocess/README.md
@@ -20,9 +20,9 @@ The platform-aware dispose ladder resolves only once the child has ACTUALLY exit
 
 1. stdin EOF (when stdin is piped), then wait `graces.disposeEofGraceMs` — a cooperative child quiesces on its own, its flushes and nested-subprocess teardown intact;
 2. on POSIX, `SIGTERM`, then wait `graces.disposeGraceMs`;
-3. force termination and await exit — `SIGKILL` on POSIX and Node's `TerminateProcess` mapping on Windows.
+3. force termination — `SIGKILL` on POSIX and Node's `TerminateProcess` mapping on Windows — then wait at most `graces.disposeGraceMs` for exit; a signal error or missing exit rejects disposal.
 
-The two graces (`DisposeLadderGraces`) come from the consuming plugin's `disposeEofGraceMs`/`disposeGraceMs` Config fields; `disposeGraceMs` is unused on Windows because Node maps `SIGTERM` and `SIGKILL` to the same forced termination. The EOF window is deliberately separate and usually wider, since cooperative teardown may await a signal-trapping grandchild plus a final flush.
+The two graces (`DisposeLadderGraces`) come from the consuming plugin's `disposeEofGraceMs`/`disposeGraceMs` Config fields. POSIX uses `disposeGraceMs` after both the graceful and forced signals; Windows skips the redundant graceful signal but uses it to bound forced-exit confirmation. The EOF window is deliberately separate and usually wider, since cooperative teardown may await a signal-trapping grandchild plus a final flush.
 
 The exit waits are internal to this ladder. They clean up their timer and listener on either outcome, so escalation never accumulates listeners on the child.
 
diff --git a/packages/subagent/subagent-subprocess/src/index.ts b/packages/subagent/subagent-subprocess/src/index.ts
index de4702bac9..47a97bafb6 100644
--- a/packages/subagent/subagent-subprocess/src/index.ts
+++ b/packages/subagent/subagent-subprocess/src/index.ts
@@ -51,16 +51,6 @@ export function spawnFailure(child: ChildProcess): Promise<Error> {
   })
 }
 
-/**
- * Resolve once the child process exits (any code/signal); immediate if it is
- * already gone.
- * @param child - the child process to await.
- */
-function waitForExit(child: ChildProcess): Promise<void> {
-  if (child.exitCode !== null || child.signalCode !== null) return Promise.resolve()
-  return new Promise<void>(resolve => child.once('exit', () => { resolve() }))
-}
-
 /**
  * Race the child's exit against a timer. Neither outcome leaves anything
  * behind on the child: the exit listener is removed on timeout and the timer
@@ -104,10 +94,49 @@ export interface DisposeLadderGraces {
    * headroom.
    */
   disposeEofGraceMs: number
-  /** POSIX tier-2 window (ms): between `SIGTERM` and the `SIGKILL` escalation. */
+  /**
+   * Termination confirmation window (ms): POSIX applies it after `SIGTERM` and again after
+   * `SIGKILL`; Windows applies it after the direct forced termination.
+   */
   disposeGraceMs: number
 }
 
+/** Force-terminate a child and reject if no exit edge arrives within the configured grace. */
+function forceTerminateWithin(child: ChildProcess, ms: number): Promise<void> {
+  if (child.exitCode !== null || child.signalCode !== null) return Promise.resolve()
+  return new Promise<void>((resolve, reject) => {
+    let accepted = false
+    let settled = false
+    const cleanup = (): void => {
+      clearTimeout(timer)
+      child.off('exit', onExit)
+      child.off('error', onError)
+    }
+    const settle = (complete: () => void): void => {
+      if (settled) return
+      settled = true
+      cleanup()
+      complete()
+    }
+    const onExit = (): void => { settle(resolve) }
+    const onError = (error: Error): void => { settle(() => { reject(error) }) }
+    child.once('exit', onExit)
+    child.once('error', onError)
+    const timer = setTimeout(() => {
+      const disposition = accepted ? 'accepted' : 'refused'
+      settle(() => {
+        reject(new Error(`child process did not exit within ${ms}ms after SIGKILL was ${disposition}`))
+      })
+    }, ms).unref()
+    try {
+      accepted = child.kill('SIGKILL')
+      if (child.exitCode !== null || child.signalCode !== null) settle(resolve)
+    } catch (error: unknown) {
+      settle(() => { reject(new Error('SIGKILL failed', { cause: error })) })
+    }
+  })
+}
+
 /**
  * Tear a child process down to quiescence, resolving only after exit: close stdin and allow
  * cooperative flush, then use the host's graceful and forced termination semantics. POSIX
@@ -117,6 +146,8 @@ export interface DisposeLadderGraces {
  * @param child - the child process to tear down.
  * @param graces - the two grace periods, from the consuming plugin's Config.
  * @param platform - the host platform, injectable for unit coverage.
+ * @throws When forced termination errors or the child does not report exit within
+ * `disposeGraceMs`.
  */
 export async function disposeChildProcess(
   child: ChildProcess,
@@ -133,9 +164,8 @@ export async function disposeChildProcess(
     child.kill('SIGTERM')
     if (await exitsWithin(child, graces.disposeGraceMs)) return
   }
-  // 3. Force-kill and await the (now-certain) exit.
-  child.kill('SIGKILL')
-  await waitForExit(child)
+  // 3. Force-kill and await a bounded exit edge.
+  await forceTerminateWithin(child, graces.disposeGraceMs)
 }
 
 /**
diff --git a/packages/subagent/subagent-subprocess/tests/subagent-subprocess.spec.ts b/packages/subagent/subagent-subprocess/tests/subagent-subprocess.spec.ts
index 901989e074..7c17333c03 100644
--- a/packages/subagent/subagent-subprocess/tests/subagent-subprocess.spec.ts
+++ b/packages/subagent/subagent-subprocess/tests/subagent-subprocess.spec.ts
@@ -234,6 +234,71 @@ describe('disposeChildProcess', () => {
     expect(fake.kills).toEqual(['SIGKILL'])
     expect(fake.signalCode).toBe('SIGKILL')
   })
+
+  it('propagates a forced-termination error without waiting for the grace', async () => {
+    const fake = new FakeChild()
+    const failure = Object.assign(new Error('kill EPERM'), { code: 'EPERM' })
+    vi.spyOn(fake, 'kill').mockImplementation((signal) => {
+      fake.kills.push(signal)
+      fake.emit('error', failure)
+      return false
+    })
+
+    await expect(disposeChildProcess(
+      asChild(fake),
+      { disposeEofGraceMs: 1, disposeGraceMs: 1000 },
+      'win32',
+    )).rejects.toBe(failure)
+    expect(fake.kills).toEqual(['SIGKILL'])
+    expect(fake.listenerCount('error')).toBe(0)
+    expect(fake.listenerCount('exit')).toBe(0)
+  })
+
+  it('wraps a synchronous forced-termination exception and removes its listeners', async () => {
+    const fake = new FakeChild()
+    const failure = new Error('invalid signal state')
+    vi.spyOn(fake, 'kill').mockImplementation(() => { throw failure })
+
+    await expect(disposeChildProcess(
+      asChild(fake),
+      { disposeEofGraceMs: 1, disposeGraceMs: 1000 },
+      'win32',
+    )).rejects.toMatchObject({ message: 'SIGKILL failed', cause: failure })
+    expect(fake.listenerCount('error')).toBe(0)
+    expect(fake.listenerCount('exit')).toBe(0)
+  })
+
+  it('bounds a refused forced termination that produces no error or exit', async () => {
+    const fake = new FakeChild()
+    vi.spyOn(fake, 'kill').mockImplementation((signal) => {
+      fake.kills.push(signal)
+      return false
+    })
+
+    await expect(disposeChildProcess(
+      asChild(fake),
+      { disposeEofGraceMs: 1, disposeGraceMs: 10 },
+      'win32',
+    )).rejects.toThrow('child process did not exit within 10ms after SIGKILL was refused')
+    expect(fake.listenerCount('error')).toBe(0)
+    expect(fake.listenerCount('exit')).toBe(0)
+  })
+
+  it('bounds an accepted forced termination that never reports exit', async () => {
+    const fake = new FakeChild()
+    vi.spyOn(fake, 'kill').mockImplementation((signal) => {
+      fake.kills.push(signal)
+      return true
+    })
+
+    await expect(disposeChildProcess(
+      asChild(fake),
+      { disposeEofGraceMs: 1, disposeGraceMs: 10 },
+      'win32',
+    )).rejects.toThrow('child process did not exit within 10ms after SIGKILL was accepted')
+    expect(fake.listenerCount('error')).toBe(0)
+    expect(fake.listenerCount('exit')).toBe(0)
+  })
 })
 
 describe('createIsolatedConfigDir', () => {