Consistent Tab IDs & Global Tag Targeting (#892)

Introduces stable per-tab IDs and a global `--tab <id>` flag for scoping individual commands to a specific tab.

Breaking change: response payloads for `tab_list`, `tab_new`, `tab_switch`, `tab_close`, and `window_new` now use `tabId` instead of `index`. `tab_close` returns `{tabId, closed: true}` instead of `{closed, activeIndex}`. `agent-browser tab <unknown>` now errors instead of silently listing tabs.

Follow-up PR to land immediately after this fixes a compile error on the provider direct-page path, clears per-tab daemon state around scoped switches, and implements active-tab restoration so `--tab N` is non-intrusive as intended.

cli/src/flags.rs

@@ -57,6 +57,7 @@ pub struct Config {
     pub json: Option<bool>,
     pub debug: Option<bool>,
     pub session: Option<String>,
+    pub tab: Option<u32>,
     pub session_name: Option<String>,
     pub executable_path: Option<String>,
     pub extensions: Option<Vec<String>>,
@@ -98,6 +99,7 @@ impl Config {
             json: other.json.or(self.json),
             debug: other.debug.or(self.debug),
             session: other.session.or(self.session),
+            tab: other.tab.or(self.tab),
             session_name: other.session_name.or(self.session_name),
             executable_path: other.executable_path.or(self.executable_path),
             extensions: match (self.extensions, other.extensions) {
@@ -196,6 +198,7 @@ fn parse_bool_arg(args: &[String], i: usize) -> (bool, bool) {
 fn extract_config_path(args: &[String]) -> Option<Option<String>> {
     const FLAGS_WITH_VALUE: &[&str] = &[
         "--session",
+        "--tab",
         "--headers",
         "--executable-path",
         "--cdp",
@@ -273,6 +276,7 @@ pub struct Flags {
     pub headed: bool,
     pub debug: bool,
     pub session: String,
+    pub tab: Option<u32>,
     pub headers: Option<String>,
     pub executable_path: Option<String>,
     pub cdp: Option<String>,
@@ -355,6 +359,7 @@ pub fn parse_flags(args: &[String]) -> Flags {
             .ok()
             .or(config.session)
             .unwrap_or_else(|| "default".to_string()),
+        tab: config.tab,
         headers: config.headers,
         executable_path: env::var("AGENT_BROWSER_EXECUTABLE_PATH")
             .ok()
@@ -492,6 +497,12 @@ pub fn parse_flags(args: &[String]) -> Flags {
                     i += 1;
                 }
             }
+            "--tab" => {
+                if let Some(s) = args.get(i + 1) {
+                    flags.tab = s.parse::<u32>().ok();
+                    i += 1;
+                }
+            }
             "--idle-timeout" => {
                 if let Some(s) = args.get(i + 1) {
                     match parse_idle_timeout(s) {
@@ -775,6 +786,7 @@ pub fn clean_args(args: &[String]) -> Vec<String> {
     // Global flags that always take a value (need to skip the next arg too)
     const GLOBAL_FLAGS_WITH_VALUE: &[&str] = &[
         "--session",
+        "--tab",
         "--headers",
         "--executable-path",
         "--cdp",
@@ -1441,4 +1453,25 @@ mod tests {
         let clean = clean_args(&input);
         assert_eq!(clean, vec!["open", "example.com"]);
     }
+
+    // === Tab flag tests ===
+
+    #[test]
+    fn test_parse_tab_flag() {
+        let flags = parse_flags(&args("--tab 4 snapshot"));
+        assert_eq!(flags.tab, Some(4));
+    }
+
+    #[test]
+    fn test_clean_args_removes_tab_flag() {
+        let cleaned = clean_args(&args("--tab 4 snapshot"));
+        assert_eq!(cleaned, vec!["snapshot"]);
+    }
+
+    #[test]
+    fn test_parse_tab_config() {
+        let json = r#"{"tab": 4}"#;
+        let config: Config = serde_json::from_str(json).unwrap();
+        assert_eq!(config.tab, Some(4));
+    }
 }