diff --git a/packages/memory-host-sdk/src/host/qmd-process.test.ts b/packages/memory-host-sdk/src/host/qmd-process.test.ts
index 7ceaf03c8ac..8abf1324882 100644
--- a/packages/memory-host-sdk/src/host/qmd-process.test.ts
+++ b/packages/memory-host-sdk/src/host/qmd-process.test.ts
@@ -3,7 +3,17 @@ import { EventEmitter } from "node:events";
 import fs from "node:fs/promises";
 import os from "node:os";
 import path from "node:path";
-import { afterAll, afterEach, beforeAll, beforeEach, describe, expect, it, vi } from "vitest";
+import {
+  afterAll,
+  afterEach,
+  beforeAll,
+  beforeEach,
+  describe,
+  expect,
+  it,
+  vi,
+  type MockInstance,
+} from "vitest";
 import { MAX_SAFE_TIMEOUT_DELAY_MS } from "../../../gateway-client/src/timeouts.js";
 
 const spawnMock = vi.hoisted(() => vi.fn());
@@ -24,13 +34,15 @@ import {
   type QmdBinaryAvailability,
 } from "./qmd-process.js";
 
-function createMockChild() {
+function createMockChild(params: { pid?: number } = {}) {
   const child = new EventEmitter() as EventEmitter & {
+    pid?: number;
     stdout: EventEmitter;
     stderr: EventEmitter;
     kill: ReturnType<typeof vi.fn>;
     closeWith: (code?: number | null, signal?: NodeJS.Signals | null) => void;
   };
+  child.pid = params.pid;
   child.stdout = new EventEmitter();
   child.stderr = new EventEmitter();
   child.kill = vi.fn();
@@ -42,7 +54,7 @@ function createMockChild() {
 
 let fixtureRoot = "";
 let tempDir = "";
-let platformSpy: { mockRestore(): void } | null = null;
+let platformSpy: MockInstance<() => NodeJS.Platform> | null = null;
 let fixtureId = 0;
 const originalPath = process.env.PATH;
 const originalPathExt = process.env.PATHEXT;
@@ -69,6 +81,7 @@ afterEach(() => {
   vi.useRealTimers();
   process.env.PATH = originalPath;
   process.env.PATHEXT = originalPathExt;
+  platformSpy?.mockReturnValue("win32");
   spawnMock.mockReset();
   tempDir = "";
 });
@@ -218,6 +231,34 @@ describe("checkQmdBinaryAvailability", () => {
 
     expect(timeoutSpy).toHaveBeenCalledWith(expect.any(Function), MAX_SAFE_TIMEOUT_DELAY_MS);
   });
+
+  it("kills timed-out availability probes by process group on POSIX", async () => {
+    platformSpy?.mockReturnValue("linux");
+    const killProcess = vi.spyOn(process, "kill").mockImplementation(() => true);
+    const child = createMockChild({ pid: 4321 });
+    spawnMock.mockReturnValueOnce(child);
+
+    try {
+      await expect(
+        checkQmdBinaryAvailability({
+          command: "qmd",
+          env: process.env,
+          cwd: tempDir,
+          timeoutMs: 1,
+        }),
+      ).resolves.toEqual({
+        available: false,
+        reason: "binary",
+        error: "spawn qmd timed out after 1ms",
+      });
+
+      expect(spawnMock.mock.calls[0]?.[2]).toMatchObject({ detached: true });
+      expect(killProcess).toHaveBeenCalledWith(-4321, "SIGKILL");
+      expect(child.kill).not.toHaveBeenCalledWith("SIGKILL");
+    } finally {
+      killProcess.mockRestore();
+    }
+  });
 });
 
 describe("runCliCommand", () => {
@@ -341,4 +382,33 @@ describe("runCliCommand", () => {
 
     expect(timeoutSpy).toHaveBeenCalledWith(expect.any(Function), MAX_SAFE_TIMEOUT_DELAY_MS);
   });
+
+  it("kills timed-out cli command process groups on POSIX", async () => {
+    platformSpy?.mockReturnValue("linux");
+    const killProcess = vi.spyOn(process, "kill").mockImplementation(() => true);
+    const child = createMockChild({ pid: 8765 });
+    spawnMock.mockReturnValueOnce(child);
+
+    try {
+      const pending = runCliCommand({
+        commandSummary: "qmd query test",
+        spawnInvocation: { command: "qmd", argv: ["query", "test", "--json"] },
+        env: process.env,
+        cwd: tempDir,
+        maxOutputChars: 10_000,
+        timeoutMs: 1,
+      });
+      const timeoutAssertion = expect(pending).rejects.toThrow(
+        "qmd query test timed out after 1ms",
+      );
+
+      await timeoutAssertion;
+
+      expect(spawnMock.mock.calls[0]?.[2]).toMatchObject({ detached: true });
+      expect(killProcess).toHaveBeenCalledWith(-8765, "SIGKILL");
+      expect(child.kill).not.toHaveBeenCalledWith("SIGKILL");
+    } finally {
+      killProcess.mockRestore();
+    }
+  });
 });
diff --git a/packages/memory-host-sdk/src/host/qmd-process.ts b/packages/memory-host-sdk/src/host/qmd-process.ts
index d40bd96b17b..37a16589b18 100644
--- a/packages/memory-host-sdk/src/host/qmd-process.ts
+++ b/packages/memory-host-sdk/src/host/qmd-process.ts
@@ -11,6 +11,11 @@ export type CliSpawnInvocation = {
   windowsHide?: boolean;
 };
 
+type QmdChildProcess = {
+  pid?: number;
+  kill: (signal?: NodeJS.Signals) => boolean;
+};
+
 export type QmdBinaryUnavailableReason = "binary" | "workspace-cwd";
 
 export type QmdBinaryUnavailable = {
@@ -92,10 +97,11 @@ export async function checkQmdBinaryAvailability(params: {
       shell: spawnInvocation.shell,
       windowsHide: spawnInvocation.windowsHide,
       stdio: "ignore",
+      detached: shouldUseQmdProcessGroup(),
     });
     const timeoutMs = resolveSafeTimeoutDelayMs(params.timeoutMs ?? 2_000, { minMs: 0 });
     const timer = setTimeout(() => {
-      child.kill("SIGKILL");
+      signalQmdProcessTree(child, "SIGKILL");
       finish({
         available: false,
         reason: "binary",
@@ -108,7 +114,7 @@ export async function checkQmdBinaryAvailability(params: {
     });
     child.once("spawn", () => {
       didSpawn = true;
-      child.kill();
+      signalQmdProcessTree(child);
       finish({ available: true });
     });
     child.once("close", () => {
@@ -162,6 +168,7 @@ export async function runCliCommand(params: {
       cwd: params.cwd,
       shell: params.spawnInvocation.shell,
       windowsHide: params.spawnInvocation.windowsHide,
+      detached: shouldUseQmdProcessGroup(),
     });
     let stdout = "";
     let stderr = "";
@@ -172,7 +179,7 @@ export async function runCliCommand(params: {
       params.timeoutMs === undefined ? undefined : resolveSafeTimeoutDelayMs(params.timeoutMs);
     const timer = timeoutMs
       ? setTimeout(() => {
-          child.kill("SIGKILL");
+          signalQmdProcessTree(child, "SIGKILL");
           reject(new Error(`${params.commandSummary} timed out after ${timeoutMs}ms`));
         }, timeoutMs)
       : null;
@@ -224,6 +231,30 @@ export async function runCliCommand(params: {
   });
 }
 
+function shouldUseQmdProcessGroup(): boolean {
+  return process.platform !== "win32";
+}
+
+function signalQmdProcessTree(child: QmdChildProcess, signal?: NodeJS.Signals): void {
+  if (shouldUseQmdProcessGroup() && typeof child.pid === "number") {
+    try {
+      if (signal === undefined) {
+        process.kill(-child.pid);
+      } else {
+        process.kill(-child.pid, signal);
+      }
+      return;
+    } catch {
+      // Fall back to the direct child if the process group already disappeared.
+    }
+  }
+  if (signal === undefined) {
+    child.kill();
+  } else {
+    child.kill(signal);
+  }
+}
+
 class CliCommandError extends Error {
   readonly code: number | null;
   readonly signal: NodeJS.Signals | null;