WIP: streamer Start takes a ctx; README and TODO

Model: opus-5-5

internal/streamer/streamer.go

@@ -188,8 +188,9 @@ func (s *Streamer) RegisterRawHandler(handler RawMessageHandler) {
 // Start begins streaming BGP updates from the RIS Live API in a background goroutine.
 // It starts worker goroutines for each registered handler and manages automatic
 // reconnection with exponential backoff on connection failures.
-// Returns an error if the streamer is already running.
-func (s *Streamer) Start() error {
+// Returns an error if the streamer is already running. It streams until Stop:
+// the end of ctx does not stop it.
+func (s *Streamer) Start(ctx context.Context) error {
 	s.mu.Lock()
 	defer s.mu.Unlock()
 
@@ -197,7 +198,7 @@ func (s *Streamer) Start() error {
 		return errAlreadyRunning
 	}
 
-	ctx, cancel := context.WithCancel(context.Background())
+	ctx, cancel := context.WithCancel(context.WithoutCancel(ctx))
 	s.cancel = cancel
 	s.running = true