llm, mlxrunner: fix done channel value consumed by first receiver

Receiving from a buffered chan error consumes the value, so only the
first caller (WaitUntilRunning, HasExited, or Close) sees the signal.
Subsequent receivers block or take the wrong branch. Replace with a
closed chan struct{} which can be received from any number of times,
and store the error in a separate field.

llm/server.go

@@ -87,7 +87,8 @@ type LlamaServer interface {
 type llmServer struct {
 	port      int
 	cmd       *exec.Cmd
-	done      chan error // Channel to signal when the process exits
+	done      chan struct{} // closed when the process exits
+	doneErr   error         // valid after done is closed
 	status    *StatusWriter
 	options   api.Options
 	modelPath string
@@ -280,7 +281,7 @@ func NewLlamaServer(systemInfo ml.SystemInfo, gpus []ml.DeviceInfo, modelPath st
 		sem:            semaphore.NewWeighted(int64(numParallel)),
 		totalLayers:    f.KV().BlockCount() + 1,
 		loadStart:      time.Now(),
-		done:           make(chan error, 1),
+		done:           make(chan struct{}),
 	}
 
 	if err != nil {
@@ -304,10 +305,11 @@ func NewLlamaServer(systemInfo ml.SystemInfo, gpus []ml.DeviceInfo, modelPath st
 			if strings.Contains(s.status.LastErrMsg, "unknown model") {
 				s.status.LastErrMsg = "this model is not supported by your version of Ollama. You may need to upgrade"
 			}
-			s.done <- errors.New(s.status.LastErrMsg)
+			s.doneErr = errors.New(s.status.LastErrMsg)
 		} else {
-			s.done <- err
+			s.doneErr = err
 		}
+		close(s.done)
 	}()
 
 	if tok != nil {
@@ -1356,8 +1358,8 @@ func (s *llmServer) WaitUntilRunning(ctx context.Context) error {
 		case <-ctx.Done():
 			slog.Warn("client connection closed before server finished loading, aborting load")
 			return fmt.Errorf("timed out waiting for llama runner to start: %w", ctx.Err())
-		case err := <-s.done:
-			return fmt.Errorf("llama runner process has terminated: %w", err)
+		case <-s.done:
+			return fmt.Errorf("llama runner process has terminated: %w", s.doneErr)
 		default:
 		}
 		if time.Now().After(stallTimer) {

x/mlxrunner/client.go

@@ -37,7 +37,8 @@ type Client struct {
 	modelName     string
 	contextLength atomic.Int64
 	memory        atomic.Uint64
-	done          chan error
+	done          chan struct{}
+	doneErr       error // valid after done is closed
 	client        *http.Client
 	status        *statusWriter
 	mu            sync.Mutex
@@ -108,7 +109,7 @@ func NewClient(modelName string) (*Client, error) {
 
 	c := &Client{
 		modelName: modelName,
-		done:      make(chan error, 1),
+		done:      make(chan struct{}),
 		client:    &http.Client{Timeout: 10 * time.Minute},
 	}
 
@@ -131,11 +132,11 @@ func (c *Client) WaitUntilRunning(ctx context.Context) error {
 		select {
 		case <-ctx.Done():
 			return ctx.Err()
-		case err := <-c.done:
+		case <-c.done:
 			if msg := c.status.getLastErr(); msg != "" {
-				return fmt.Errorf("mlx runner failed: %s (exit: %v)", msg, err)
+				return fmt.Errorf("mlx runner failed: %s (exit: %v)", msg, c.doneErr)
 			}
-			return fmt.Errorf("mlx runner exited unexpectedly: %w", err)
+			return fmt.Errorf("mlx runner exited unexpectedly: %w", c.doneErr)
 		case <-timeout:
 			if msg := c.status.getLastErr(); msg != "" {
 				return fmt.Errorf("timeout waiting for mlx runner: %s", msg)
@@ -411,8 +412,8 @@ func (c *Client) Load(ctx context.Context, _ ml.SystemInfo, gpus []ml.DeviceInfo
 
 	// Reap subprocess when it exits
 	go func() {
-		err := cmd.Wait()
-		c.done <- err
+		c.doneErr = cmd.Wait()
+		close(c.done)
 	}()
 
 	return nil, nil