[fix](trx-server): fix satellite pass computation degrading spectrum performance

Two issues introduced with wxsat/satellite support caused indirect
performance degradation on the spectrum rendering path:

1. spawn_tle_refresh_task() was called inside spawn_rig_audio_stack(),
   which runs per-rig. With N rigs this spawned N redundant TLE refresh
   tasks, each making 3 concurrent HTTP requests to CelesTrak and
   competing for write locks on the global TLE store. Moved to a single
   global call after the per-rig loop.

2. compute_upcoming_passes() (SGP4 propagation for 200+ satellites over
   24h = ~300K propagation steps) ran on every GetSatPasses request with
   no caching. Multiple client connections could trigger concurrent
   CPU-heavy computations, causing cache pollution and tokio runtime
   contention that indirectly slowed spectrum frame processing. Added a
   60-second server-side cache shared across all client connections.

https://claude.ai/code/session_017g7VNMb6CChaiWrfzVBhbR
Signed-off-by: Claude <noreply@anthropic.com>

src/trx-server/src/listener.rs

@@ -13,8 +13,8 @@
 use std::collections::HashMap;
 use std::collections::HashSet;
 use std::net::SocketAddr;
-use std::sync::Arc;
-use std::time::Duration;
+use std::sync::{Arc, Mutex};
+use std::time::{Duration, Instant};
 
 use tokio::io::{AsyncBufRead, AsyncBufReadExt, AsyncWriteExt, BufReader};
 use tokio::net::{TcpListener, TcpStream};
@@ -35,6 +35,16 @@ use crate::rig_handle::RigHandle;
 const IO_TIMEOUT: Duration = Duration::from_secs(10);
 const REQUEST_TIMEOUT: Duration = Duration::from_secs(12);
 const MAX_JSON_LINE_BYTES: usize = 256 * 1024;
+/// How long to cache satellite pass predictions before recomputing.
+/// SGP4 propagation for 200+ satellites is CPU-intensive; caching avoids
+/// redundant recomputation when multiple clients request passes concurrently.
+const SAT_PASS_CACHE_TTL: Duration = Duration::from_secs(60);
+
+/// Cached satellite pass prediction result shared across client connections.
+struct SatPassCache {
+    result: trx_core::geo::PassPredictionResult,
+    computed_at: Instant,
+}
 /// Run the JSON TCP listener, accepting client connections.
 ///
 /// `rigs` is a shared map from rig_id → `RigHandle`.  The first entry (by
@@ -51,6 +61,7 @@ pub async fn run_listener(
     let listener = TcpListener::bind(addr).await?;
     info!("Listening on {}", addr);
     let validator = Arc::new(SimpleTokenValidator::new(auth_tokens));
+    let sat_pass_cache: Arc<Mutex<Option<SatPassCache>>> = Arc::new(Mutex::new(None));
 
     loop {
         tokio::select! {
@@ -63,8 +74,9 @@ pub async fn run_listener(
                 let validator = Arc::clone(&validator);
                 let client_shutdown_rx = shutdown_rx.clone();
                 let coords = station_coords;
+                let cache = Arc::clone(&sat_pass_cache);
                 tokio::spawn(async move {
-                    if let Err(e) = handle_client(socket, peer, rigs, default_rig_id, validator, coords, client_shutdown_rx).await {
+                    if let Err(e) = handle_client(socket, peer, rigs, default_rig_id, validator, coords, cache, client_shutdown_rx).await {
                         error!("Client {} error: {:?}", peer, e);
                     }
                 });
@@ -161,6 +173,7 @@ async fn handle_client(
     default_rig_id: String,
     validator: Arc<SimpleTokenValidator>,
     station_coords: Option<(f64, f64)>,
+    sat_pass_cache: Arc<Mutex<Option<SatPassCache>>>,
     mut shutdown_rx: watch::Receiver<bool>,
 ) -> std::io::Result<()> {
     let (reader, mut writer) = socket.into_split();
@@ -271,15 +284,32 @@ async fn handle_client(
         }
 
         // GetSatPasses: compute satellite passes from the server-side TLE store.
-        // Runs on a blocking thread to avoid stalling the connection handler.
+        // Results are cached for SAT_PASS_CACHE_TTL to avoid redundant CPU-heavy
+        // SGP4 propagation when multiple clients request passes concurrently.
         if matches!(envelope.cmd, ClientCommand::GetSatPasses) {
-            let result = if let Some((lat, lon)) = station_coords {
+            // Check cache first.
+            let cached = sat_pass_cache
+                .lock()
+                .ok()
+                .and_then(|guard| {
+                    guard.as_ref().and_then(|c| {
+                        if c.computed_at.elapsed() < SAT_PASS_CACHE_TTL {
+                            Some(c.result.clone())
+                        } else {
+                            None
+                        }
+                    })
+                });
+
+            let result = if let Some(cached_result) = cached {
+                cached_result
+            } else if let Some((lat, lon)) = station_coords {
                 let now_ms = std::time::SystemTime::now()
                     .duration_since(std::time::UNIX_EPOCH)
                     .unwrap_or_default()
                     .as_millis() as i64;
                 let window_ms = 24 * 3600 * 1000; // 24 hours
-                tokio::task::spawn_blocking(move || {
+                let fresh = tokio::task::spawn_blocking(move || {
                     trx_core::geo::compute_upcoming_passes(lat, lon, now_ms, window_ms)
                 })
                 .await
@@ -287,7 +317,15 @@ async fn handle_client(
                     passes: vec![],
                     satellite_count: 0,
                     tle_source: trx_core::geo::TleSource::Unavailable,
-                })
+                });
+                // Update cache.
+                if let Ok(mut guard) = sat_pass_cache.lock() {
+                    *guard = Some(SatPassCache {
+                        result: fresh.clone(),
+                        computed_at: Instant::now(),
+                    });
+                }
+                fresh
             } else {
                 trx_core::geo::PassPredictionResult {
                     passes: vec![],

src/trx-server/src/main.rs

@@ -794,9 +794,6 @@ fn spawn_rig_audio_stack(
             }
         }));
 
-        // Start periodic TLE refresh from CelesTrak (on start + once/day).
-        trx_core::geo::spawn_tle_refresh_task();
-
         // Spawn weather satellite APT decoder task
         let wxsat_pcm_rx = pcm_tx.subscribe();
         let wxsat_state_rx = state_rx.clone();
@@ -1145,6 +1142,11 @@ async fn main() -> DynResult<()> {
     // Spawn periodic flush of decode history to disk (every 60 s).
     history_store::spawn_flush_task(history_db, rig_histories_for_flush);
 
+    // Start periodic TLE refresh from CelesTrak (on start + once/day).
+    // Called once globally rather than per-rig to avoid redundant HTTP fetches
+    // and write-lock contention on the TLE store.
+    trx_core::geo::spawn_tle_refresh_task();
+
     // Start JSON TCP listener.
     if cfg.listen.enabled {
         let listen_ip = cli.listen.unwrap_or(cfg.listen.listen);