diff --git a/src/agents/session-write-lock.ts b/src/agents/session-write-lock.ts
index 6c6bf89745..94d43d5ac8 100644
--- a/src/agents/session-write-lock.ts
+++ b/src/agents/session-write-lock.ts
@@ -1,6 +1,7 @@
 import fsSync from "node:fs";
 import fs from "node:fs/promises";
 import path from "node:path";
+import { isPidAlive } from "../shared/pid-alive.js";
 
 type LockFilePayload = {
   pid: number;
@@ -48,18 +49,6 @@ function resolveCleanupState(): CleanupState {
   return proc[CLEANUP_STATE_KEY];
 }
 
-function isAlive(pid: number): boolean {
-  if (!Number.isFinite(pid) || pid <= 0) {
-    return false;
-  }
-  try {
-    process.kill(pid, 0);
-    return true;
-  } catch {
-    return false;
-  }
-}
-
 /**
  * Synchronously release all held locks.
  * Used during process exit when async operations aren't reliable.
@@ -206,7 +195,7 @@ export async function acquireSessionWriteLock(params: {
       const payload = await readLockPayload(lockPath);
       const createdAt = payload?.createdAt ? Date.parse(payload.createdAt) : NaN;
       const stale = !Number.isFinite(createdAt) || Date.now() - createdAt > staleMs;
-      const alive = payload?.pid ? isAlive(payload.pid) : false;
+      const alive = payload?.pid ? isPidAlive(payload.pid) : false;
       if (stale || !alive) {
         await fs.rm(lockPath, { force: true });
         continue;
diff --git a/src/infra/gateway-lock.ts b/src/infra/gateway-lock.ts
index ef89f42a10..d6dbf2266a 100644
--- a/src/infra/gateway-lock.ts
+++ b/src/infra/gateway-lock.ts
@@ -3,6 +3,7 @@ import fsSync from "node:fs";
 import fs from "node:fs/promises";
 import path from "node:path";
 import { resolveConfigPath, resolveGatewayLockDir, resolveStateDir } from "../config/paths.js";
+import { isPidAlive } from "../shared/pid-alive.js";
 
 const DEFAULT_TIMEOUT_MS = 5000;
 const DEFAULT_POLL_INTERVAL_MS = 100;
@@ -42,18 +43,6 @@ export class GatewayLockError extends Error {
 
 type LockOwnerStatus = "alive" | "dead" | "unknown";
 
-function isAlive(pid: number): boolean {
-  if (!Number.isFinite(pid) || pid <= 0) {
-    return false;
-  }
-  try {
-    process.kill(pid, 0);
-    return true;
-  } catch {
-    return false;
-  }
-}
-
 function normalizeProcArg(arg: string): string {
   return arg.replaceAll("\\", "/").toLowerCase();
 }
@@ -116,7 +105,7 @@ function resolveGatewayOwnerStatus(
   payload: LockPayload | null,
   platform: NodeJS.Platform,
 ): LockOwnerStatus {
-  if (!isAlive(pid)) {
+  if (!isPidAlive(pid)) {
     return "dead";
   }
   if (platform !== "linux") {
diff --git a/src/plugin-sdk/file-lock.ts b/src/plugin-sdk/file-lock.ts
index 2e38607da6..9bbf2e5b6c 100644
--- a/src/plugin-sdk/file-lock.ts
+++ b/src/plugin-sdk/file-lock.ts
@@ -1,5 +1,6 @@
 import fs from "node:fs/promises";
 import path from "node:path";
+import { isPidAlive } from "../shared/pid-alive.js";
 
 export type FileLockOptions = {
   retries: {
@@ -37,18 +38,6 @@ function resolveHeldLocks(): Map<string, HeldLock> {
 
 const HELD_LOCKS = resolveHeldLocks();
 
-function isAlive(pid: number): boolean {
-  if (!Number.isFinite(pid) || pid <= 0) {
-    return false;
-  }
-  try {
-    process.kill(pid, 0);
-    return true;
-  } catch {
-    return false;
-  }
-}
-
 function computeDelayMs(retries: FileLockOptions["retries"], attempt: number): number {
   const base = Math.min(
     retries.maxTimeout,
@@ -85,7 +74,7 @@ async function resolveNormalizedFilePath(filePath: string): Promise<string> {
 
 async function isStaleLock(lockPath: string, staleMs: number): Promise<boolean> {
   const payload = await readLockPayload(lockPath);
-  if (payload?.pid && !isAlive(payload.pid)) {
+  if (payload?.pid && !isPidAlive(payload.pid)) {
     return true;
   }
   if (payload?.createdAt) {
diff --git a/src/shared/pid-alive.ts b/src/shared/pid-alive.ts
new file mode 100644
index 0000000000..a1e9c84eac
--- /dev/null
+++ b/src/shared/pid-alive.ts
@@ -0,0 +1,11 @@
+export function isPidAlive(pid: number): boolean {
+  if (!Number.isFinite(pid) || pid <= 0) {
+    return false;
+  }
+  try {
+    process.kill(pid, 0);
+    return true;
+  } catch {
+    return false;
+  }
+}