diff --git a/src/core/process-lifecycle.ts b/src/core/process-lifecycle.ts
index f9256f8..f7949e2 100644
--- a/src/core/process-lifecycle.ts
+++ b/src/core/process-lifecycle.ts
@@ -27,6 +27,7 @@ export interface IdleMonitor {
 export interface IdleMonitorOptions {
   timeoutMs: number;
   onIdle: () => void;
+  isTransportAlive?: () => boolean;
 }
 
 export interface ParentMonitorOptions {
@@ -89,6 +90,10 @@ export function createIdleMonitor(options: IdleMonitorOptions): IdleMonitor {
     if (timer) clearTimeout(timer);
     timer = setTimeout(() => {
       timer = null;
+      if (options.isTransportAlive && options.isTransportAlive()) {
+        schedule();
+        return;
+      }
       options.onIdle();
     }, options.timeoutMs);
     unrefHandle(timer);
diff --git a/src/index.ts b/src/index.ts
index dc4a514..e688e3a 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -549,6 +549,7 @@ async function main() {
   const idleMonitor = createIdleMonitor({
     timeoutMs: getIdleShutdownMs(process.env.CONTEXTPLUS_IDLE_TIMEOUT_MS),
     onIdle: () => requestShutdown("idle-timeout", 0),
+    isTransportAlive: () => process.stdin.readable && !process.stdin.destroyed,
   });
 
   noteServerActivity = idleMonitor.touch;
diff --git a/test/main/idle-timeout-spawn.test.mjs b/test/main/idle-timeout-spawn.test.mjs
new file mode 100644
index 0000000..3085f7a
--- /dev/null
+++ b/test/main/idle-timeout-spawn.test.mjs
@@ -0,0 +1,147 @@
+import { describe, it } from "node:test";
+import assert from "node:assert/strict";
+import { spawn } from "node:child_process";
+import { resolve, dirname, join } from "node:path";
+import { fileURLToPath } from "node:url";
+import { mkdtempSync, writeFileSync } from "node:fs";
+import { tmpdir } from "node:os";
+import {
+  createIdleMonitor,
+} from "../../build/core/process-lifecycle.js";
+
+const PROJECT_ROOT = resolve(dirname(fileURLToPath(import.meta.url)), "../..");
+
+function wait(ms) {
+  return new Promise((resolve) => setTimeout(resolve, ms));
+}
+
+function createTestScript(withFix) {
+  const buildPath = join(PROJECT_ROOT, "build/core/process-lifecycle.js").replace(/\\/g, "/");
+  return `
+    import { createIdleMonitor } from "file://${buildPath}";
+
+    const idleMonitor = createIdleMonitor({
+      timeoutMs: 200,
+      onIdle: () => {
+        process.stderr.write("IDLE_SHUTDOWN\\n");
+        process.exit(0);
+      },
+      ${withFix ? 'isTransportAlive: () => process.stdin.readable && !process.stdin.destroyed,' : ''}
+    });
+
+    process.stderr.write("STARTED\\n");
+    const keepAlive = setInterval(() => {}, 1000);
+    setTimeout(() => {
+      idleMonitor.stop();
+      clearInterval(keepAlive);
+      process.stderr.write("SURVIVED\\n");
+      process.exit(0);
+    }, 1500);
+  `;
+}
+
+function runHarness(withFix) {
+  return new Promise((resolve) => {
+    const tmpDir = mkdtempSync(join(tmpdir(), "cp-test-"));
+    const scriptPath = join(tmpDir, "harness.mjs");
+    writeFileSync(scriptPath, createTestScript(withFix));
+
+    const child = spawn("node", [scriptPath], {
+      stdio: ["pipe", "pipe", "pipe"],
+    });
+
+    let stderr = "";
+    child.stderr.on("data", (d) => { stderr += d.toString(); });
+
+    child.on("exit", (code) => {
+      resolve({ code, stderr });
+    });
+  });
+}
+
+describe("idle-timeout transport-aware fix", () => {
+  it("does NOT fire onIdle when isTransportAlive returns true", async () => {
+    let idleFired = 0;
+    const monitor = createIdleMonitor({
+      timeoutMs: 30,
+      onIdle: () => { idleFired += 1; },
+      isTransportAlive: () => true,
+    });
+    await wait(80);
+    assert.equal(idleFired, 0, "onIdle should not fire when transport is alive");
+    monitor.stop();
+  });
+
+  it("fires onIdle when isTransportAlive returns false", async () => {
+    let idleFired = 0;
+    const monitor = createIdleMonitor({
+      timeoutMs: 30,
+      onIdle: () => { idleFired += 1; },
+      isTransportAlive: () => false,
+    });
+    await wait(80);
+    assert.equal(idleFired, 1, "onIdle should fire when transport is dead");
+    monitor.stop();
+  });
+
+  it("fires onIdle normally when no isTransportAlive provided (backward compat)", async () => {
+    let idleFired = 0;
+    const monitor = createIdleMonitor({
+      timeoutMs: 30,
+      onIdle: () => { idleFired += 1; },
+    });
+    await wait(80);
+    assert.equal(idleFired, 1, "onIdle should fire with no transport check");
+    monitor.stop();
+  });
+
+  it("reschedules then fires when transport dies after initial alive check", async () => {
+    let transportAlive = true;
+    let idleFired = 0;
+    const monitor = createIdleMonitor({
+      timeoutMs: 30,
+      onIdle: () => { idleFired += 1; },
+      isTransportAlive: () => transportAlive,
+    });
+    await wait(50);
+    assert.equal(idleFired, 0, "should not fire while transport alive");
+    transportAlive = false;
+    await wait(50);
+    assert.equal(idleFired, 1, "should fire after transport dies");
+    monitor.stop();
+  });
+
+  it("touch resets the idle timer even with transport check", async () => {
+    let idleFired = 0;
+    const monitor = createIdleMonitor({
+      timeoutMs: 40,
+      onIdle: () => { idleFired += 1; },
+      isTransportAlive: () => false,
+    });
+    await wait(20);
+    monitor.touch();
+    await wait(20);
+    assert.equal(idleFired, 0, "touch should reset timer");
+    await wait(30);
+    assert.equal(idleFired, 1, "should fire after full timeout post-touch");
+    monitor.stop();
+  });
+
+  it("spawn: without isTransportAlive, server exits on idle with stdin open", async () => {
+    const result = await runHarness(false);
+    assert.equal(result.code, 0);
+    assert.ok(result.stderr.includes("IDLE_SHUTDOWN"),
+      "server idle-shutdown with stdin open (no transport check)");
+    assert.ok(!result.stderr.includes("SURVIVED"),
+      "server died before survival window");
+  });
+
+  it("spawn: with isTransportAlive, server survives idle when stdin is open", async () => {
+    const result = await runHarness(true);
+    assert.equal(result.code, 0);
+    assert.ok(!result.stderr.includes("IDLE_SHUTDOWN"),
+      "server should NOT idle-shutdown when transport alive");
+    assert.ok(result.stderr.includes("SURVIVED"),
+      "server should survive past idle timeout");
+  });
+});