diff --git a/src/infra/gateway-lock.test.ts b/src/infra/gateway-lock.test.ts
index b4250647efe6..85cb777e8b5c 100644
--- a/src/infra/gateway-lock.test.ts
+++ b/src/infra/gateway-lock.test.ts
@@ -377,6 +377,36 @@ describe("gateway lock", () => {
     openSpy.mockRestore();
   });
 
+  it("closes handle and removes lock file when writeFile fails after open succeeds", async () => {
+    vi.useRealTimers();
+    const env = await makeEnv();
+    const { lockPath } = resolveLockPath(env);
+
+    const writeError = Object.assign(new Error("ENOSPC: no space left on device"), {
+      code: "ENOSPC",
+    });
+    const close = vi.fn<() => Promise<void>>().mockResolvedValue(undefined);
+    const mockHandle = {
+      writeFile: vi.fn().mockImplementation(async () => {
+        await fs.writeFile(lockPath, "partial", "utf8");
+        throw writeError;
+      }),
+      close,
+    };
+
+    const openSpy = vi.spyOn(fs, "open").mockResolvedValueOnce(mockHandle as never);
+
+    await expect(acquireForTest(env)).rejects.toMatchObject({
+      name: "GatewayLockError",
+      cause: writeError,
+    });
+
+    expect(close).toHaveBeenCalledTimes(1);
+    await expect(fs.access(lockPath)).rejects.toMatchObject({ code: "ENOENT" });
+
+    openSpy.mockRestore();
+  });
+
   it("clears stale lock on win32 when process cmdline is not a gateway", async () => {
     vi.useRealTimers();
     const env = await makeEnv();
diff --git a/src/infra/gateway-lock.ts b/src/infra/gateway-lock.ts
index 6454dbac0026..acfab7030f64 100644
--- a/src/infra/gateway-lock.ts
+++ b/src/infra/gateway-lock.ts
@@ -262,16 +262,24 @@ export async function acquireGatewayLock(
   while (now() - startedAt < timeoutMs) {
     try {
       const handle = await fs.open(lockPath, "wx");
-      const startTime = platform === "linux" ? readLinuxStartTime(process.pid) : null;
-      const payload: LockPayload = {
-        pid: process.pid,
-        createdAt: resolveTimestampMsToIsoString(now()),
-        configPath,
-      };
-      if (typeof startTime === "number" && Number.isFinite(startTime)) {
-        payload.startTime = startTime;
+      try {
+        const startTime = platform === "linux" ? readLinuxStartTime(process.pid) : null;
+        const payload: LockPayload = {
+          pid: process.pid,
+          createdAt: resolveTimestampMsToIsoString(now()),
+          configPath,
+        };
+        if (typeof startTime === "number" && Number.isFinite(startTime)) {
+          payload.startTime = startTime;
+        }
+        await handle.writeFile(JSON.stringify(payload), "utf8");
+      } catch (error) {
+        // Acquisition owns both resources until the release callback exists.
+        // Unwind them if payload preparation fails before ownership transfers.
+        await handle.close().catch(() => undefined);
+        await fs.rm(lockPath, { force: true }).catch(() => undefined);
+        throw error;
       }
-      await handle.writeFile(JSON.stringify(payload), "utf8");
       return {
         lockPath,
         configPath,