diff --git a/src/acp-agent.ts b/src/acp-agent.ts
index 3abceac..a6be9d3 100644
--- a/src/acp-agent.ts
+++ b/src/acp-agent.ts
@@ -958,6 +958,11 @@ export class ClaudeAcpAgent implements Agent {
     delete this.sessions[sessionId];
   }
 
+  /** Tear down all active sessions. Called when the ACP connection closes. */
+  async dispose(): Promise<void> {
+    await Promise.all(Object.keys(this.sessions).map((id) => this.teardownSession(id)));
+  }
+
   async unstable_closeSession(params: CloseSessionRequest): Promise<CloseSessionResponse> {
     if (!this.sessions[params.sessionId]) {
       throw new Error("Session not found");
@@ -2239,7 +2244,12 @@ export function runAcp() {
   const output = nodeToWebReadable(process.stdin);
 
   const stream = ndJsonStream(input, output);
-  new AgentSideConnection((client) => new ClaudeAcpAgent(client), stream);
+  let agent!: ClaudeAcpAgent;
+  const connection = new AgentSideConnection((client) => {
+    agent = new ClaudeAcpAgent(client);
+    return agent;
+  }, stream);
+  return { connection, agent };
 }
 
 function commonPrefixLength(a: string, b: string) {
diff --git a/src/index.ts b/src/index.ts
index d45d290..88efcdf 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -24,8 +24,18 @@ if (process.argv.includes("--cli")) {
     console.error("Unhandled Rejection at:", promise, "reason:", reason);
   });
 
-  runAcp();
+  const { connection, agent } = runAcp();
 
-  // Keep process alive
+  // Exit cleanly when the ACP connection closes (e.g. stdin EOF, transport
+  // error). Without this, `process.stdin.resume()` keeps the event loop
+  // alive indefinitely, causing orphan process accumulation in oneshot mode.
+  connection.closed.then(async () => {
+    await agent.dispose().catch((err) => {
+      console.error("Error during cleanup:", err);
+    });
+    process.exit(0);
+  });
+
+  // Keep process alive while connection is open
   process.stdin.resume();
 }