Fix cross-runtime panic in mix-fetch when timed-out requests receive

late error injection
- Add early return in reject() when request is already gone from Rust
  map
- Replace panic with log + return in SendError and InjectData

wasm/mix-fetch/go-mix-conn/internal/state/state.go

@@ -92,7 +92,8 @@ func (ar *CurrentActiveRequests) InjectData(id types.RequestId, data []byte) {
 	defer ar.Unlock()
 	_, exists := ar.Requests[id]
 	if !exists {
-		panic("attempted to write to connection that doesn't exist")
+		log.Error("attempted to inject data for connection %d that no longer exists — likely already cleaned up", id)
+		return
 	}
 	ar.Requests[id].injector.ServerData <- data
 }
@@ -115,7 +116,8 @@ func (ar *CurrentActiveRequests) SendError(id types.RequestId, err error) {
 	defer ar.Unlock()
 	_, exists := ar.Requests[id]
 	if !exists {
-		panic("attempted to inject error data to connection that doesn't exist")
+		log.Error("attempted to inject error for connection %d that no longer exists — likely already cleaned up", id)
+		return
 	}
 	ar.Requests[id].injector.RemoteError <- err
 }

wasm/mix-fetch/src/active_requests.rs

@@ -69,7 +69,8 @@ impl ActiveRequests {
         let mut guard = self.inner.lock().await;
         let old = guard.remove(&id);
         if old.is_none() {
-            console_error!("attempted to reject request {id}, but it seems to have never existed?")
+            console_error!("attempted to reject request {id}, but it no longer exists — likely already cleaned up by Go timeout");
+            return;
         }
 
         goWasmInjectConnError(id.to_string(), err.to_string())