diff --git a/src/cli/program.ts b/src/cli/program.ts
index 424d81dbc..12f45c7d8 100644
--- a/src/cli/program.ts
+++ b/src/cli/program.ts
@@ -8,6 +8,7 @@ import { statusCommand } from "../commands/status.js";
 import { loadConfig } from "../config/config.js";
 import { danger, info, setVerbose } from "../globals.js";
 import { startControlChannel } from "../infra/control-channel.js";
+import { acquireRelayLock, RelayLockError } from "../infra/relay-lock.js";
 import { getResolvedLoggerSettings } from "../logging.js";
 import {
   loginWeb,
@@ -383,6 +384,18 @@ Examples:
       const { file: logFile, level: logLevel } = getResolvedLoggerSettings();
       defaultRuntime.log(info(`logs: ${logFile} (level ${logLevel})`));
 
+      let releaseRelayLock: (() => Promise<void>) | null = null;
+      try {
+        releaseRelayLock = await acquireRelayLock();
+      } catch (err) {
+        if (err instanceof RelayLockError) {
+          defaultRuntime.error(danger(`Relay already running: ${err.message}`));
+          defaultRuntime.exit(1);
+          return;
+        }
+        throw err;
+      }
+
       const providerOpt = (opts.provider ?? "auto").toLowerCase();
       const cfg = loadConfig();
       const telegramToken =
@@ -589,6 +602,7 @@ Examples:
         defaultRuntime.error(danger(`Relay failed: ${String(err)}`));
         defaultRuntime.exit(1);
       } finally {
+        if (releaseRelayLock) await releaseRelayLock();
         if (control) await control.close();
       }
     });
diff --git a/src/infra/relay-lock.test.ts b/src/infra/relay-lock.test.ts
new file mode 100644
index 000000000..d931ed940
--- /dev/null
+++ b/src/infra/relay-lock.test.ts
@@ -0,0 +1,29 @@
+import fs from "node:fs";
+import os from "node:os";
+import path from "node:path";
+
+import { describe, expect, it } from "vitest";
+
+import { acquireRelayLock, RelayLockError } from "./relay-lock.js";
+
+const newLockPath = () =>
+  path.join(os.tmpdir(), `clawdis-relay-lock-test-${process.pid}-${Math.random().toString(16).slice(2)}.sock`);
+
+describe("relay-lock", () => {
+  it("prevents concurrent relay instances and releases cleanly", async () => {
+    const lockPath = newLockPath();
+
+    const release1 = await acquireRelayLock(lockPath);
+    expect(fs.existsSync(lockPath)).toBe(true);
+
+    await expect(acquireRelayLock(lockPath)).rejects.toBeInstanceOf(RelayLockError);
+
+    await release1();
+    expect(fs.existsSync(lockPath)).toBe(false);
+
+    // After release, lock can be reacquired.
+    const release2 = await acquireRelayLock(lockPath);
+    await release2();
+    expect(fs.existsSync(lockPath)).toBe(false);
+  });
+});
diff --git a/src/infra/relay-lock.ts b/src/infra/relay-lock.ts
new file mode 100644
index 000000000..40a60db3e
--- /dev/null
+++ b/src/infra/relay-lock.ts
@@ -0,0 +1,94 @@
+import fs from "node:fs";
+import net from "node:net";
+import os from "node:os";
+import path from "node:path";
+
+const DEFAULT_LOCK_PATH = path.join(os.tmpdir(), "clawdis-relay.lock");
+
+export class RelayLockError extends Error {}
+
+type ReleaseFn = () => Promise<void>;
+
+/**
+ * Acquire an exclusive single-instance lock for the relay using a Unix domain socket.
+ *
+ * Why a socket? If the process crashes or is SIGKILLed, the socket file remains but
+ * the next start will detect ECONNREFUSED when connecting and clean the stale path
+ * before retrying. This keeps the lock self-healing without manual pidfile cleanup.
+ */
+export async function acquireRelayLock(lockPath = DEFAULT_LOCK_PATH): Promise<ReleaseFn> {
+  // Fast path: try to listen on the lock path.
+  const attemptListen = (): Promise<net.Server> =>
+    new Promise((resolve, reject) => {
+      const server = net.createServer();
+
+      server.once("error", async (err: NodeJS.ErrnoException) => {
+        if (err.code !== "EADDRINUSE") {
+          reject(new RelayLockError(`lock listen failed: ${err.message}`));
+          return;
+        }
+
+        // Something is already bound. Try to connect to see if it is alive.
+        const client = net.connect({ path: lockPath });
+
+        client.once("connect", () => {
+          client.destroy();
+          reject(new RelayLockError("another relay instance is already running"));
+        });
+
+        client.once("error", (connErr: NodeJS.ErrnoException) => {
+          // Nothing is listening -> stale socket file. Remove and retry once.
+          if (connErr.code === "ECONNREFUSED" || connErr.code === "ENOENT") {
+            try {
+              fs.rmSync(lockPath, { force: true });
+            } catch (rmErr) {
+              reject(
+                new RelayLockError(
+                  `failed to clean stale lock at ${lockPath}: ${String(rmErr)}`,
+                ),
+              );
+              return;
+            }
+            attemptListen().then(resolve, reject);
+            return;
+          }
+
+          reject(
+            new RelayLockError(
+              `failed to connect to existing lock (${lockPath}): ${connErr.message}`,
+            ),
+          );
+        });
+      });
+
+      server.listen(lockPath, () => resolve(server));
+    });
+
+  const server = await attemptListen();
+
+  let released = false;
+  const release = async (): Promise<void> => {
+    if (released) return;
+    released = true;
+    await new Promise<void>((resolve) => server.close(() => resolve()));
+    try {
+      fs.rmSync(lockPath, { force: true });
+    } catch {
+      /* ignore */
+    }
+  };
+
+  const cleanupSignals: NodeJS.Signals[] = ["SIGINT", "SIGTERM", "SIGHUP"];
+  const handleSignal = async () => {
+    await release();
+    process.exit(0);
+  };
+
+  cleanupSignals.forEach((sig) => process.once(sig, handleSignal));
+  process.once("exit", () => {
+    // Exit handler must be sync-safe; release is async but close+rm are fast.
+    void release();
+  });
+
+  return release;
+}