Add configurable session idle timeout option

docs/features/session-persistence.md

@@ -433,14 +433,26 @@ await client.deleteSession("user-123-task-456");
 
 ## Automatic Cleanup: Idle Timeout
 
-The CLI has a built-in 30-minute idle timeout. Sessions without activity are automatically cleaned up:
+By default, sessions have **no idle timeout** and live indefinitely until explicitly disconnected or deleted. You can optionally configure a server-wide idle timeout via `CopilotClientOptions.sessionIdleTimeoutSeconds`:
+
+```typescript
+const client = new CopilotClient({
+  sessionIdleTimeoutSeconds: 30 * 60, // 30 minutes
+});
+```
+
+When a timeout is configured, sessions without activity for that duration are automatically cleaned up. The minimum value is 300 seconds (5 minutes). Set to `0` or omit to disable.
+
+> **Note:** This option only applies when the SDK spawns the runtime process. When connecting to an existing server via `cliUrl`, the server's own timeout configuration applies.
 
 ```mermaid
 flowchart LR
-    A["⚡ Last Activity"] --> B["⏳ 25 min<br/>timeout_warning"] --> C["🧹 30 min<br/>destroyed"]
+    A["⚡ Last Activity"] --> B["⏳ ~5 min before<br/>timeout_warning"] --> C["🧹 Timeout<br/>destroyed"]
 ```
 
-Listen for idle events to know when work completes:
+Sessions with active work (running commands, background agents) are always protected from idle cleanup, regardless of the timeout setting.
+
+Listen for idle events to react to session inactivity:
 
 ```typescript
 session.on("session.idle", (event) => {

nodejs/src/client.ts

@@ -339,6 +339,7 @@ export class CopilotClient {
             // Default useLoggedInUser to false when githubToken is provided, otherwise true
             useLoggedInUser: options.useLoggedInUser ?? (options.githubToken ? false : true),
             telemetry: options.telemetry,
+            sessionIdleTimeoutSeconds: options.sessionIdleTimeoutSeconds ?? 0,
         };
     }
 
@@ -1385,6 +1386,16 @@ export class CopilotClient {
                 args.push("--no-auto-login");
             }
 
+            if (
+                this.options.sessionIdleTimeoutSeconds !== undefined &&
+                this.options.sessionIdleTimeoutSeconds > 0
+            ) {
+                args.push(
+                    "--session-idle-timeout",
+                    this.options.sessionIdleTimeoutSeconds.toString()
+                );
+            }
+
             // Suppress debug/trace output that might pollute stdout
             const envWithoutNodeDebug = { ...this.options.env };
             delete envWithoutNodeDebug.NODE_DEBUG;

nodejs/src/types.ts

@@ -182,6 +182,15 @@ export interface CopilotClientOptions {
      * instead of the server's default local filesystem storage.
      */
     sessionFs?: SessionFsConfig;
+
+    /**
+     * Server-wide idle timeout for sessions in seconds.
+     * Sessions without activity for this duration are automatically cleaned up.
+     * Set to 0 or omit to disable (sessions live indefinitely).
+     * Minimum value: 300 (5 minutes).
+     * @default undefined (disabled)
+     */
+    sessionIdleTimeoutSeconds?: number;
 }
 
 /**