feat(session): support unfocused agent windows (--no-focus) (#87)

`bsk session start --no-focus` opens the Agent Window in the background
without stealing focus. The flag threads focused=false through
CLI -> daemon IPC -> tool.session_start -> chrome.windows.create; an
omitted `focused` keeps the extension default (true) so older clients
are unaffected.

Reworked onto current main so it composes with #52 window sizing:
AgentWindowApi.create / SessionManager.start (extension), start_session
(CLI) and the daemon's session start now take options objects/structs
({ size, focused }) instead of colliding positional params.

Co-authored-by: alectimison-maker <alec.timison@gmail.com>

crates/bsk-cli/src/cli/record.rs

@@ -17,7 +17,7 @@ use crate::cli::business_rpc;
 use crate::cli::ensure_daemon::ensure_daemon;
 use crate::cli::error::{CliError, Format};
 use crate::cli::record_state;
-use crate::cli::session::{start_session, stop_session};
+use crate::cli::session::{SessionStartOptions, start_session, stop_session};
 
 /// Max wait for the user to click 结束 in the browser (24 hours).
 const RECORD_AWAIT_TIMEOUT_MS: u32 = 86_400_000;
@@ -85,7 +85,13 @@ fn dispatch_start(args: RecordStartArgs, format: Format) -> Result<(), CliError>
     }
 
     let info = ensure_daemon().context("ensure daemon is running")?;
-    let session = start_session(info.sock_path.clone(), args.browser, None, None)?;
+    let session = start_session(
+        info.sock_path.clone(),
+        SessionStartOptions {
+            browser: args.browser,
+            ..SessionStartOptions::default()
+        },
+    )?;
 
     let start_params = RecordStartParams {
         session_id: session.session_id.clone(),

crates/bsk-cli/src/cli/session.rs

@@ -64,6 +64,10 @@ pub struct SessionStartArgs {
     /// `--width` and `--height` must be given to take effect.
     #[arg(long, value_parser = window_size)]
     pub height: Option<u32>,
+
+    /// Open the Agent Window in the background without stealing focus.
+    #[arg(long)]
+    pub no_focus: bool,
 }
 
 /// Parse a `--width` / `--height` Agent Window dimension (CSS pixels).
@@ -99,6 +103,8 @@ struct StartParams {
     width: Option<u32>,
     #[serde(skip_serializing_if = "Option::is_none")]
     height: Option<u32>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    focused: Option<bool>,
 }
 
 #[derive(Debug, Deserialize)]
@@ -173,7 +179,15 @@ fn run_start(sock: PathBuf, args: SessionStartArgs, format: Format) -> Result<()
             }
         });
     }
-    let result = start_session(sock, args.browser, args.width, args.height);
+    let result = start_session(
+        sock,
+        SessionStartOptions {
+            browser: args.browser,
+            width: args.width,
+            height: args.height,
+            focused: args.no_focus.then_some(false),
+        },
+    );
     waited.store(true, Ordering::SeqCst);
     match result {
         Ok(reply) => match format {
@@ -197,20 +211,27 @@ fn run_start(sock: PathBuf, args: SessionStartArgs, format: Format) -> Result<()
     Ok(())
 }
 
+/// Options for [`start_session`]: browser selection plus Agent Window
+/// creation hints. `None` fields keep the extension-side defaults
+/// (focused window, browser-chosen size).
+#[derive(Debug, Default, Clone)]
+pub struct SessionStartOptions {
+    pub browser: Option<String>,
+    pub width: Option<u32>,
+    pub height: Option<u32>,
+    pub focused: Option<bool>,
+}
+
 /// Start a session and open the Agent Window. Used by `session start` and `record start`.
-pub fn start_session(
-    sock: PathBuf,
-    browser: Option<String>,
-    width: Option<u32>,
-    height: Option<u32>,
-) -> Result<StartReply, CliError> {
+pub fn start_session(sock: PathBuf, opts: SessionStartOptions) -> Result<StartReply, CliError> {
     call(
         sock,
         Method::SessionStart,
         Some(StartParams {
-            browser_instance_id: browser,
-            width,
-            height,
+            browser_instance_id: opts.browser,
+            width: opts.width,
+            height: opts.height,
+            focused: opts.focused,
         }),
         SESSION_START_IPC_TIMEOUT,
     )