fix(attach): resolve exec startup-size race and non-blocking resize sends

Author: thejoeejoee

internal/cmd/attach.go

@@ -348,9 +348,15 @@ func attachExec(ctx context.Context, client *docker.Client, dir string, session
 			defer close(sigDone)
 			for {
 				select {
-			case <-sigCh:
-				if w, h, err := term.GetSize(fd); err == nil {
-						resizeCh <- docker.TerminalSize{Width: uint(w), Height: uint(h)} //nolint:gosec // terminal dimensions are always positive
+				case <-sigCh:
+					if w, h, err := term.GetSize(fd); err == nil {
+						size := docker.TerminalSize{Width: uint(w), Height: uint(h)} //nolint:gosec // terminal dimensions are always positive
+						select {
+						case resizeCh <- size:
+						default:
+							<-resizeCh
+							resizeCh <- size
+						}
 					}
 				case <-ctx.Done():
 					return
@@ -373,9 +379,15 @@ func attachExec(ctx context.Context, client *docker.Client, dir string, session
 			defer ticker.Stop()
 			for {
 				select {
-			case <-ticker.C:
-				if w, h, err := term.GetSize(fd); err == nil && (w != lastW || h != lastH) {
-						resizeCh <- docker.TerminalSize{Width: uint(w), Height: uint(h)} //nolint:gosec // terminal dimensions are always positive
+				case <-ticker.C:
+					if w, h, err := term.GetSize(fd); err == nil && (w != lastW || h != lastH) {
+						size := docker.TerminalSize{Width: uint(w), Height: uint(h)} //nolint:gosec // terminal dimensions are always positive
+						select {
+						case resizeCh <- size:
+						default:
+							<-resizeCh
+							resizeCh <- size
+						}
 						lastW, lastH = w, h
 					}
 				case <-ctx.Done():

internal/docker/docker.go

@@ -334,6 +334,16 @@ func (c *Client) ExecInteractive(ctx context.Context, containerID string, args [
 		Tty:          true,
 	}
 
+	// Apply initial terminal size before starting the exec so the process
+	// launches with the correct dimensions (avoids startup-size race).
+	if resizeCh != nil {
+		select {
+		case size := <-resizeCh:
+			execCfg.ConsoleSize = &[2]uint{size.Height, size.Width}
+		default:
+		}
+	}
+
 	execResp, err := engineCli.ContainerExecCreate(ctx, containerID, execCfg)
 	if err != nil {
 		return fmt.Errorf("create exec in container %s: %w", containerID, err)