feat(cleanup): default idle-shutdown + keep — stop leaving scratch tabs/groups behind

Agents finish a task and just stop (never calling `close`), so daemons used to
run forever, leaving their per-session scratch tabs + tab group in the user's
Chrome. Two cases now handled:

- Default idle timeout (10 min; AGENT_BROWSER_IDLE_TIMEOUT_MS overrides, 0
  disables). On idle the daemon close()s the tabs IT created → the empty tab
  group is auto-removed by Chrome. Timer resets on every command, so active
  sessions are untouched. Adopted user tabs are never owned, so never closed.
- `keep` — leave the ACTIVE tab for the user: unown it (exempt from
  close/idle) + ask the extension to ungroup it (ABExt.ungroupTab → 0.4.12) so
  it becomes a normal tab. Scratch gets cleaned, deliverable tabs stay.

Also fix two clippy violations in the concurrently-landed #47 viewport code
(manual char comparison + iter().any→contains) that were failing main's CI.

ext 0.4.12: handle ABExt.ungroupTab (chrome.tabs.ungroup). 870 tests pass.

cli/src/native/actions.rs

@@ -1317,6 +1317,7 @@ pub async fn execute_command(cmd: &Value, state: &mut DaemonState) -> Value {
         "evaluate" => handle_evaluate(cmd, state).await,
         "site" => handle_site(cmd, state).await,
         "close" => handle_close(state).await,
+        "keep" => handle_keep(state).await,
         "stealth_status" => handle_stealth_status(state).await,
         "snapshot" => handle_snapshot(cmd, state).await,
         "screenshot" => handle_screenshot(cmd, state).await,
@@ -2855,6 +2856,34 @@ async fn handle_stealth_status(state: &DaemonState) -> Result<Value, String> {
     }))
 }
 
+/// `keep` — leave the ACTIVE tab for the user: stop owning it (so the daemon's
+/// `close()`/idle-shutdown won't close it) and best-effort remove it from this
+/// session's tab group so it looks like a normal user tab. The "leave for the
+/// user" half of the auto-close-on-idle cleanup: scratch tabs get closed, tabs
+/// the agent explicitly `keep`s stay. (Adopted user tabs are never owned, so
+/// they're already safe.)
+async fn handle_keep(state: &mut DaemonState) -> Result<Value, String> {
+    let mgr = state.browser.as_mut().ok_or("Browser not launched")?;
+    let target_id = mgr.active_target_id()?.to_string();
+    let session_id = mgr.active_session_id()?.to_string();
+    let was_owned = mgr.unown_target(&target_id);
+    // Best-effort: ask the extension to ungroup the tab (relay only; no-ops on a
+    // launched browser or an older extension that doesn't know ABExt.ungroupTab).
+    let _ = mgr
+        .client
+        .send_command_typed::<_, Value>(
+            "ABExt.ungroupTab",
+            &json!({ "sessionId": session_id, "targetId": target_id }),
+            None,
+        )
+        .await;
+    Ok(json!({
+        "kept": target_id,
+        "wasOwned": was_owned,
+        "note": "tab left for the user — exempt from auto-close, removed from the session tab group",
+    }))
+}
+
 async fn handle_close(state: &mut DaemonState) -> Result<Value, String> {
     if let Some(ref mgr) = state.browser {
         if let Some(ref session_name) = state.session_name {

cli/src/native/browser.rs

@@ -1546,6 +1546,13 @@ impl BrowserManager {
             .ok_or_else(|| "No active page".to_string())
     }
 
+    /// Stop owning a tab — drop it from `created_targets` so it survives `close()`
+    /// and idle-shutdown (the agent is leaving it for the user). Returns true if it
+    /// was owned. Used by `keep`.
+    pub fn unown_target(&mut self, target_id: &str) -> bool {
+        self.created_targets.remove(target_id)
+    }
+
     /// Returns true if this manager was connected via CDP (as opposed to local launch).
     pub fn is_cdp_connection(&self) -> bool {
         self.browser_process.is_none()

cli/src/native/daemon.rs

@@ -130,12 +130,21 @@ pub async fn run_daemon(session: &str) {
         }
     }
 
-    // Auto-shutdown the daemon after this many ms of inactivity (no commands received).
-    // Disabled when unset or 0.
-    let idle_timeout_ms = env::var("AGENT_BROWSER_IDLE_TIMEOUT_MS")
-        .ok()
-        .and_then(|s| s.parse::<u64>().ok())
-        .filter(|&ms| ms > 0);
+    // Auto-shutdown the daemon after this many ms of inactivity (no commands
+    // received). On shutdown the daemon closes the tabs IT created (its per-session
+    // tab group), so an agent that finishes a task and just stops — without ever
+    // calling `close` — no longer leaves a pile of scratch tabs and a lingering
+    // tab group in the user's Chrome. The timer resets on every command, so active
+    // sessions are never interrupted; only genuinely-idle ones clean up.
+    //
+    // Defaults to 10 minutes. Set AGENT_BROWSER_IDLE_TIMEOUT_MS to override, or 0
+    // to disable (keep the daemon alive forever — the old behaviour). Adopted
+    // tabs (the user's own, via `adopt`) are never closed: only `created_targets`.
+    const DEFAULT_IDLE_TIMEOUT_MS: u64 = 600_000;
+    let idle_timeout_ms = match env::var("AGENT_BROWSER_IDLE_TIMEOUT_MS") {
+        Ok(s) => s.trim().parse::<u64>().ok().filter(|&ms| ms > 0),
+        Err(_) => Some(DEFAULT_IDLE_TIMEOUT_MS),
+    };
 
     let result = run_socket_server(
         &socket_path,