feat: read the viewport payload's explicit active field

Current compositors send {text: <tab markup>, active: N}; prefer the
field and keep the Pan-text parse as the fallback for the old
camera-state payload.

Co-Authored-By: Claude Fable 5 <[email protected]>

 src/main.rs | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/src/main.rs b/src/main.rs
index de6ab44..b663165 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -958,6 +958,14 @@ fn get_closest_viewport(x: f64, y: f64) -> i32 {
 fn get_active_viewport_from_camera(viewport_json: &str) -> u32 {
     let mut text = viewport_json.to_string();
     if let Ok(val) = serde_json::from_str::<serde_json::Value>(viewport_json) {
+        // Current compositors send the active viewport explicitly alongside
+        // the tab markup; the Pan-text parse below is the fallback for the
+        // old camera-state payload.
+        if let Some(a) = val.get("active").and_then(|v| v.as_u64()) {
+            if (1..=4).contains(&a) {
+                return a as u32;
+            }
+        }
         if let Some(t) = val.get("text").and_then(|v| v.as_str()) {
             text = t.to_string();
         }