fix: name selected Docker connection in DMR transport errors

pkg/model/provider/dmr/dmrmodels/docker.go

@@ -3,8 +3,10 @@ package dmrmodels
 import (
 	"context"
 	"net"
+	"net/http"
 	"os/exec"
 	"slices"
+	"strings"
 )
 
 type dockerConnectionKey struct{}
@@ -33,3 +35,17 @@ func DockerCommand(ctx context.Context, args ...string) *exec.Cmd {
 	}
 	return exec.CommandContext(ctx, "docker", args...)
 }
+
+type dockerTransport struct {
+	*http.Transport
+
+	args []string
+}
+
+func (t *dockerTransport) RoundTrip(req *http.Request) (*http.Response, error) {
+	resp, err := t.Transport.RoundTrip(req)
+	if err != nil {
+		return nil, &net.OpError{Op: "docker connection", Net: strings.Join(t.args, " "), Err: err}
+	}
+	return resp, nil
+}

pkg/model/provider/dmr/dmrmodels/resolve.go

@@ -214,18 +214,20 @@ func resolvePrimaryDMRURL(ctx context.Context, endpoint string) (string, *http.C
 		baseURL := fmt.Sprintf("http://_/%s%s/v1", expPrefix, dmrInferencePrefix)
 
 		connection, _ := ctx.Value(dockerConnectionKey{}).(*dockerConnection)
-		httpClient := &http.Client{
-			Transport: &http.Transport{
-				IdleConnTimeout: 30 * time.Second,
-				DialContext: func(ctx context.Context, _, _ string) (net.Conn, error) {
-					if connection != nil {
-						return connection.dial(ctx)
-					}
-					var d net.Dialer
-					return d.DialContext(ctx, "unix", "/var/run/docker.sock")
-				},
+		transport := &http.Transport{
+			IdleConnTimeout: 30 * time.Second,
+			DialContext: func(ctx context.Context, _, _ string) (net.Conn, error) {
+				if connection != nil {
+					return connection.dial(ctx)
+				}
+				var d net.Dialer
+				return d.DialContext(ctx, "unix", "/var/run/docker.sock")
 			},
 		}
+		httpClient := &http.Client{Transport: transport}
+		if connection != nil {
+			httpClient.Transport = &dockerTransport{Transport: transport, args: connection.args}
+		}
 
 		return baseURL, httpClient
 	}

pkg/model/provider/dmr/dmrmodels/resolve_test.go

@@ -3,9 +3,13 @@ package dmrmodels
 import (
 	"context"
 	"errors"
+	"io"
 	"net"
 	"net/http"
 	"net/http/httptest"
+	"net/url"
+	"os"
+	"syscall"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -102,6 +106,59 @@ func TestResolvedDockerTransportRetainsConnection(t *testing.T) {
 	assert.Equal(t, []string{"ai/test"}, models)
 }
 
+func TestSelectedDockerTransportErrorsNameEngine(t *testing.T) {
+	if inContainer() {
+		t.Skip("Desktop engine routing is host-only")
+	}
+	t.Setenv("MODEL_RUNNER_HOST", "")
+	for _, tt := range []struct {
+		name string
+		err  error
+		dial bool
+	}{
+		{name: "dial", err: net.ErrClosed, dial: true},
+		{name: "closed pipe", err: os.ErrClosed},
+		{name: "broken pipe", err: syscall.EPIPE},
+		{name: "EOF", err: io.EOF, dial: true},
+		{name: "canceled", err: context.Canceled},
+		{name: "deadline", err: context.DeadlineExceeded, dial: true},
+	} {
+		t.Run(tt.name, func(t *testing.T) {
+			ctx := ContextWithDockerConnection(t.Context(), []string{"--host=unix:///missing-dmr-engine.sock"}, func(context.Context) (net.Conn, error) {
+				if tt.dial {
+					return nil, tt.err
+				}
+				conn, peer := net.Pipe()
+				t.Cleanup(func() { _ = peer.Close() })
+				return &failingDockerConn{Conn: conn, err: tt.err}, nil
+			})
+			baseURL, client := ResolveBaseURL(ctx, nil, defaultContainerURL())
+			require.NotNil(t, client)
+			defer client.CloseIdleConnections()
+			_, err := ListModelsAt(t.Context(), client, baseURL)
+			require.ErrorIs(t, err, tt.err)
+			require.ErrorContains(t, err, "unix:///missing-dmr-engine.sock")
+			var requestErr *url.Error
+			require.ErrorAs(t, err, &requestErr)
+			assert.Equal(t, errors.Is(tt.err, context.DeadlineExceeded), requestErr.Timeout())
+		})
+	}
+}
+
+type failingDockerConn struct {
+	net.Conn
+
+	err error
+}
+
+func (c *failingDockerConn) Read([]byte) (int, error) {
+	return 0, c.err
+}
+
+func (c *failingDockerConn) Write([]byte) (int, error) {
+	return 0, c.err
+}
+
 func TestResolveSelectedDockerDoesNotProbeFallbacks(t *testing.T) {
 	if inContainer() {
 		t.Skip("Desktop engine routing is host-only")