Resolve Client.Go-004..010 code-review findings

Client.Go-004: ran gofmt on alarms_test.go and galaxy_test.go; the tree is
now gofmt-clean.

Client.Go-005/009/010: migrated Dial/DialGalaxy off the deprecated
grpc.DialContext/WithBlock to grpc.NewClient via a shared dial helper, with
a DialTimeout-bounded readiness probe to keep fail-fast semantics; shared
callContext deadline arithmetic; updated the stale Dial doc comment. Test
harnesses use passthrough:///bufnet for the NewClient default-scheme change.

Client.Go-006: added GatewayError.Code() and an IsTransient(err) helper so
callers can classify transient gRPC failures.

Client.Go-007: newCorrelationID no longer returns an empty id when
crypto/rand fails — it falls back to a non-empty time+counter id.

Client.Go-008: added coverage_test.go for transport-credential resolution,
callContext deadline arithmetic, and native value/array edge kinds.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

clients/go/README.md

@@ -90,6 +90,19 @@ events may be lost. Raw protobuf messages remain available through the
 `errors.As` for `GatewayError`, `CommandError`, and `MxAccessError`; command
 errors preserve the raw reply.
 
+`Dial` and `DialGalaxy` create the connection lazily (`grpc.NewClient`): a
+gateway that is briefly unavailable no longer turns into a hard error — the
+connection recovers once the gateway comes up. To keep fail-fast behavior,
+both run a readiness probe bounded by `DialTimeout` (default 10s, or the
+context deadline when sooner) and return a `*GatewayError` if the gateway
+cannot be reached in that window.
+
+For retry, timeout, and auth handling, `GatewayError.Code()` exposes the
+wrapped gRPC `codes.Code`, and `mxgateway.IsTransient(err)` reports whether a
+failure (`Unavailable`, `DeadlineExceeded`, `ResourceExhausted`, `Aborted`)
+may succeed on retry — so callers do not have to unwrap the error and call
+`status.Code` themselves.
+
 ## Galaxy Repository browse
 
 The `GalaxyRepository` service (proto package `galaxy_repository.v1`) is a

clients/go/mxgateway/alarms_test.go

@@ -150,8 +150,8 @@ func TestQueryActiveAlarmsPassesFilterPrefix(t *testing.T) {
 	defer cleanup()
 
 	stream, err := client.QueryActiveAlarms(context.Background(), &pb.QueryActiveAlarmsRequest{
-		SessionId:          "session-1",
+		SessionId:         "session-1",
-		AlarmFilterPrefix:  "Tank01.",
+		AlarmFilterPrefix: "Tank01.",
 	})
 	if err != nil {
 		t.Fatalf("QueryActiveAlarms() error = %v", err)
@@ -221,8 +221,10 @@ func newBufconnClientWithAlarms(t *testing.T, fake *fakeGatewayWithAlarms) (*Cli
 	dialer := func(ctx context.Context, _ string) (net.Conn, error) {
 		return listener.DialContext(ctx)
 	}
+	// grpc.NewClient defaults to the dns scheme; use passthrough so the
+	// bufconn fake target reaches the context dialer unresolved.
 	client, err := Dial(context.Background(), Options{
-		Endpoint:    "bufnet",
+		Endpoint:    "passthrough:///bufnet",
 		APIKey:      "test-api-key",
 		Plaintext:   true,
 		DialOptions: []grpc.DialOption{grpc.WithContextDialer(dialer)},

clients/go/mxgateway/client.go

@@ -19,6 +19,7 @@ import (
 
 	pb "gitea.dohertylan.com/dohertj2/mxaccessgw/clients/go/internal/generated"
 	"google.golang.org/grpc"
+	"google.golang.org/grpc/connectivity"
 	"google.golang.org/grpc/credentials"
 	"google.golang.org/grpc/credentials/insecure"
 	"google.golang.org/protobuf/types/known/durationpb"
@@ -36,22 +37,36 @@ type Client struct {
 	opts Options
 }
 
-// Dial opens a gRPC connection to the gateway and configures auth metadata,
+// Dial opens a gRPC connection to the gateway and configures auth metadata
-// transport security, and blocking dial cancellation from ctx.
+// and transport security.
+//
+// The connection is created lazily with grpc.NewClient: the channel is not
+// established until the first RPC (or the readiness probe below) needs it, so
+// a gateway that is briefly unavailable at Dial time no longer turns into a
+// hard error — the connection recovers when the gateway comes up. To preserve
+// fail-fast behavior, Dial then runs an explicit readiness probe bounded by
+// DialTimeout (default 10s, or ctx's deadline when sooner): it triggers the
+// initial connect and waits for the channel to reach Ready, returning a
+// *GatewayError if the gateway cannot be reached in that window. Cancelling
+// ctx aborts the probe.
 func Dial(ctx context.Context, opts Options) (*Client, error) {
+	conn, err := dial(ctx, opts)
+	if err != nil {
+		return nil, err
+	}
+
+	return NewClient(conn, opts), nil
+}
+
+// dial builds the shared gRPC connection used by both Client and GalaxyClient:
+// it resolves transport credentials, assembles dial options, creates a lazy
+// connection with grpc.NewClient, and runs the DialTimeout-bounded readiness
+// probe so callers still fail fast when the gateway is unreachable.
+func dial(ctx context.Context, opts Options) (*grpc.ClientConn, error) {
 	if opts.Endpoint == "" {
 		return nil, errors.New("mxgateway: endpoint is required")
 	}
 
-	dialCtx := ctx
-	cancel := func() {}
-	if opts.DialTimeout > 0 {
-		dialCtx, cancel = context.WithTimeout(ctx, opts.DialTimeout)
-	} else if _, ok := ctx.Deadline(); !ok {
-		dialCtx, cancel = context.WithTimeout(ctx, defaultDialTimeout)
-	}
-	defer cancel()
-
 	transportCredentials, err := resolveTransportCredentials(opts)
 	if err != nil {
 		return nil, err
@@ -61,16 +76,46 @@ func Dial(ctx context.Context, opts Options) (*Client, error) {
 		grpc.WithTransportCredentials(transportCredentials),
 		grpc.WithUnaryInterceptor(unaryAuthInterceptor(opts.APIKey)),
 		grpc.WithStreamInterceptor(streamAuthInterceptor(opts.APIKey)),
-		grpc.WithBlock(),
 	}
 	dialOptions = append(dialOptions, opts.DialOptions...)
 
-	conn, err := grpc.DialContext(dialCtx, opts.Endpoint, dialOptions...)
+	conn, err := grpc.NewClient(opts.Endpoint, dialOptions...)
 	if err != nil {
 		return nil, &GatewayError{Op: "dial", Err: err}
 	}
 
-	return NewClient(conn, opts), nil
+	if err := waitForReady(ctx, conn, opts.DialTimeout); err != nil {
+		_ = conn.Close()
+		return nil, &GatewayError{Op: "dial", Err: err}
+	}
+
+	return conn, nil
+}
+
+// waitForReady triggers the initial connect on conn and blocks until the
+// channel reaches connectivity.Ready, the timeout elapses, or ctx is
+// cancelled. The wait is bounded by dialTimeout when positive, otherwise by
+// ctx's existing deadline, otherwise by defaultDialTimeout.
+func waitForReady(ctx context.Context, conn *grpc.ClientConn, dialTimeout time.Duration) error {
+	probeCtx := ctx
+	cancel := func() {}
+	if dialTimeout > 0 {
+		probeCtx, cancel = context.WithTimeout(ctx, dialTimeout)
+	} else if _, ok := ctx.Deadline(); !ok {
+		probeCtx, cancel = context.WithTimeout(ctx, defaultDialTimeout)
+	}
+	defer cancel()
+
+	conn.Connect()
+	for {
+		state := conn.GetState()
+		if state == connectivity.Ready {
+			return nil
+		}
+		if !conn.WaitForStateChange(probeCtx, state) {
+			return probeCtx.Err()
+		}
+	}
 }
 
 // NewClient wraps an existing gRPC connection. The caller owns closing conn
@@ -188,7 +233,15 @@ func (c *Client) Close() error {
 }
 
 func (c *Client) callContext(ctx context.Context) (context.Context, context.CancelFunc) {
-	timeout := c.opts.CallTimeout
+	return callContext(ctx, c.opts.CallTimeout)
+}
+
+// callContext derives a per-RPC context from ctx, applying callTimeout: zero
+// uses defaultCallTimeout, a negative value disables the bound entirely, and a
+// caller-supplied deadline that is already sooner than the derived timeout is
+// kept as-is rather than being lengthened.
+func callContext(ctx context.Context, callTimeout time.Duration) (context.Context, context.CancelFunc) {
+	timeout := callTimeout
 	if timeout == 0 {
 		timeout = defaultCallTimeout
 	}

clients/go/mxgateway/client_session_test.go

@@ -292,8 +292,11 @@ func newBufconnClient(t *testing.T, fake *fakeGatewayServer) (*Client, func()) {
 	dialer := func(ctx context.Context, _ string) (net.Conn, error) {
 		return listener.DialContext(ctx)
 	}
+	// grpc.NewClient defaults the target scheme to dns; the bufconn fake name
+	// is not DNS-resolvable, so use the passthrough scheme to hand the target
+	// straight to the context dialer.
 	client, err := Dial(context.Background(), Options{
-		Endpoint:  "bufnet",
+		Endpoint:  "passthrough:///bufnet",
 		APIKey:    "test-api-key",
 		Plaintext: true,
 		DialOptions: []grpc.DialOption{

clients/go/mxgateway/coverage_test.go

@@ -0,0 +1,401 @@
+package mxgateway
+
+import (
+	"context"
+	"crypto/tls"
+	"errors"
+	"net"
+	"reflect"
+	"strings"
+	"testing"
+	"time"
+
+	pb "gitea.dohertylan.com/dohertj2/mxaccessgw/clients/go/internal/generated"
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/credentials/insecure"
+	"google.golang.org/grpc/status"
+	"google.golang.org/protobuf/types/known/timestamppb"
+)
+
+// --- Client.Go-008: resolveTransportCredentials precedence -----------------
+
+// TestResolveTransportCredentialsPrecedence covers every branch of
+// resolveTransportCredentials, which previously only had the Plaintext path
+// exercised.
+func TestResolveTransportCredentialsPrecedence(t *testing.T) {
+	custom := insecure.NewCredentials()
+
+	t.Run("TransportCredentialsWins", func(t *testing.T) {
+		creds, err := resolveTransportCredentials(Options{
+			TransportCredentials: custom,
+			Plaintext:            true, // must be ignored
+		})
+		if err != nil {
+			t.Fatalf("unexpected error: %v", err)
+		}
+		if creds != custom {
+			t.Fatal("expected the explicit TransportCredentials to be returned as-is")
+		}
+	})
+
+	t.Run("Plaintext", func(t *testing.T) {
+		creds, err := resolveTransportCredentials(Options{Plaintext: true})
+		if err != nil {
+			t.Fatalf("unexpected error: %v", err)
+		}
+		if got := creds.Info().SecurityProtocol; got != "insecure" {
+			t.Fatalf("expected insecure credentials, got security protocol %q", got)
+		}
+	})
+
+	t.Run("CACertFileMissingErrors", func(t *testing.T) {
+		_, err := resolveTransportCredentials(Options{CACertFile: "does-not-exist.pem"})
+		if err == nil {
+			t.Fatal("expected an error for a missing CA cert file")
+		}
+	})
+
+	t.Run("TLSConfigWithServerNameOverride", func(t *testing.T) {
+		creds, err := resolveTransportCredentials(Options{
+			TLSConfig:          &tls.Config{MinVersion: tls.VersionTLS13},
+			ServerNameOverride: "gateway.internal",
+		})
+		if err != nil {
+			t.Fatalf("unexpected error: %v", err)
+		}
+		if got := creds.Info().ServerName; got != "gateway.internal" {
+			t.Fatalf("expected ServerName override to be applied, got %q", got)
+		}
+	})
+
+	t.Run("DefaultTLSFloor", func(t *testing.T) {
+		creds, err := resolveTransportCredentials(Options{ServerNameOverride: "host"})
+		if err != nil {
+			t.Fatalf("unexpected error: %v", err)
+		}
+		if got := creds.Info().SecurityProtocol; got != "tls" {
+			t.Fatalf("expected the default TLS credentials, got %q", got)
+		}
+	})
+}
+
+// TestResolveTransportCredentialsDoesNotMutateTLSConfig confirms the supplied
+// TLSConfig is cloned, not mutated, when ServerNameOverride is applied.
+func TestResolveTransportCredentialsDoesNotMutateTLSConfig(t *testing.T) {
+	cfg := &tls.Config{MinVersion: tls.VersionTLS12}
+	if _, err := resolveTransportCredentials(Options{
+		TLSConfig:          cfg,
+		ServerNameOverride: "override",
+	}); err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if cfg.ServerName != "" {
+		t.Fatalf("resolveTransportCredentials mutated the caller's TLSConfig (ServerName=%q)", cfg.ServerName)
+	}
+}
+
+// --- Client.Go-008: callContext deadline arithmetic ------------------------
+
+// TestCallContextDeadlineArithmetic covers the shared callContext deadline
+// logic, including the negative-timeout disable case and the
+// caller-deadline-is-sooner case.
+func TestCallContextDeadlineArithmetic(t *testing.T) {
+	t.Run("ZeroUsesDefault", func(t *testing.T) {
+		ctx, cancel := callContext(context.Background(), 0)
+		defer cancel()
+		deadline, ok := ctx.Deadline()
+		if !ok {
+			t.Fatal("expected a deadline for the default timeout")
+		}
+		remaining := time.Until(deadline)
+		if remaining <= 0 || remaining > defaultCallTimeout+time.Second {
+			t.Fatalf("default deadline out of range: %v", remaining)
+		}
+	})
+
+	t.Run("NegativeDisablesBound", func(t *testing.T) {
+		base := context.Background()
+		ctx, cancel := callContext(base, -1)
+		defer cancel()
+		if _, ok := ctx.Deadline(); ok {
+			t.Fatal("a negative timeout must disable the deadline entirely")
+		}
+		if ctx != base {
+			t.Fatal("a negative timeout must return the caller context unchanged")
+		}
+	})
+
+	t.Run("PositiveAppliesTimeout", func(t *testing.T) {
+		ctx, cancel := callContext(context.Background(), 5*time.Second)
+		defer cancel()
+		deadline, ok := ctx.Deadline()
+		if !ok {
+			t.Fatal("expected a deadline")
+		}
+		remaining := time.Until(deadline)
+		if remaining <= 0 || remaining > 5*time.Second+time.Second {
+			t.Fatalf("deadline out of range: %v", remaining)
+		}
+	})
+
+	t.Run("CallerDeadlineSoonerIsKept", func(t *testing.T) {
+		base, baseCancel := context.WithTimeout(context.Background(), 100*time.Millisecond)
+		defer baseCancel()
+		ctx, cancel := callContext(base, 30*time.Second)
+		defer cancel()
+		if ctx != base {
+			t.Fatal("a caller deadline sooner than the timeout must be kept as-is")
+		}
+	})
+
+	t.Run("CallerDeadlineLaterIsShortened", func(t *testing.T) {
+		base, baseCancel := context.WithTimeout(context.Background(), time.Hour)
+		defer baseCancel()
+		ctx, cancel := callContext(base, time.Second)
+		defer cancel()
+		deadline, ok := ctx.Deadline()
+		if !ok {
+			t.Fatal("expected a deadline")
+		}
+		if remaining := time.Until(deadline); remaining > 2*time.Second {
+			t.Fatalf("expected the shorter timeout to win, got %v remaining", remaining)
+		}
+	})
+}
+
+// --- Client.Go-008: NativeValue / NativeArray edge branches ----------------
+
+// TestNativeValueEdgeKinds covers the array, raw-bytes, null, and
+// nil-input branches of NativeValue.
+func TestNativeValueEdgeKinds(t *testing.T) {
+	t.Run("NilInput", func(t *testing.T) {
+		got, err := NativeValue(nil)
+		if err != nil || got != nil {
+			t.Fatalf("NativeValue(nil) = (%v, %v), want (nil, nil)", got, err)
+		}
+	})
+
+	t.Run("ExplicitNull", func(t *testing.T) {
+		got, err := NativeValue(&pb.MxValue{IsNull: true})
+		if err != nil || got != nil {
+			t.Fatalf("NativeValue(null) = (%v, %v), want (nil, nil)", got, err)
+		}
+	})
+
+	t.Run("RawBytes", func(t *testing.T) {
+		raw := []byte{0x01, 0x02, 0x03}
+		got, err := NativeValue(&pb.MxValue{Kind: &pb.MxValue_RawValue{RawValue: raw}})
+		if err != nil {
+			t.Fatalf("unexpected error: %v", err)
+		}
+		gotBytes, ok := got.([]byte)
+		if !ok || !reflect.DeepEqual(gotBytes, raw) {
+			t.Fatalf("NativeValue raw = %v, want %v", got, raw)
+		}
+		// The result must be a copy, not aliasing the protobuf field.
+		gotBytes[0] = 0xFF
+		if raw[0] != 0x01 {
+			t.Fatal("NativeValue raw result aliases the protobuf backing array")
+		}
+	})
+
+	t.Run("ArrayValue", func(t *testing.T) {
+		value := &pb.MxValue{Kind: &pb.MxValue_ArrayValue{
+			ArrayValue: &pb.MxArray{Values: &pb.MxArray_Int32Values{
+				Int32Values: &pb.Int32Array{Values: []int32{7, 8}},
+			}},
+		}}
+		got, err := NativeValue(value)
+		if err != nil {
+			t.Fatalf("unexpected error: %v", err)
+		}
+		if !reflect.DeepEqual(got, []int32{7, 8}) {
+			t.Fatalf("NativeValue array = %v, want [7 8]", got)
+		}
+	})
+}
+
+// TestNativeArrayEdgeKinds covers the nil, raw-bytes, timestamp-with-nil, and
+// unsupported-kind branches of NativeArray.
+func TestNativeArrayEdgeKinds(t *testing.T) {
+	t.Run("NilInput", func(t *testing.T) {
+		got, err := NativeArray(nil)
+		if err != nil || got != nil {
+			t.Fatalf("NativeArray(nil) = (%v, %v), want (nil, nil)", got, err)
+		}
+	})
+
+	t.Run("RawValues", func(t *testing.T) {
+		got, err := NativeArray(&pb.MxArray{Values: &pb.MxArray_RawValues{
+			RawValues: &pb.RawArray{Values: [][]byte{{0x0A}, {0x0B}}},
+		}})
+		if err != nil {
+			t.Fatalf("unexpected error: %v", err)
+		}
+		want := [][]byte{{0x0A}, {0x0B}}
+		if !reflect.DeepEqual(got, want) {
+			t.Fatalf("NativeArray raw = %v, want %v", got, want)
+		}
+	})
+
+	t.Run("TimestampWithNilEntry", func(t *testing.T) {
+		got, err := NativeArray(&pb.MxArray{Values: &pb.MxArray_TimestampValues{
+			TimestampValues: &pb.TimestampArray{Values: []*timestamppb.Timestamp{nil}},
+		}})
+		if err != nil {
+			t.Fatalf("unexpected error: %v", err)
+		}
+		times, ok := got.([]time.Time)
+		if !ok || len(times) != 1 || !times[0].IsZero() {
+			t.Fatalf("NativeArray timestamp-with-nil = %v, want [zero-time]", got)
+		}
+	})
+
+	t.Run("UnsupportedKind", func(t *testing.T) {
+		// An MxArray with no oneof set hits the default branch.
+		_, err := NativeArray(&pb.MxArray{})
+		if err == nil {
+			t.Fatal("expected an error for an MxArray with no values set")
+		}
+		if !strings.Contains(err.Error(), "unsupported array value kind") {
+			t.Fatalf("unexpected error text: %v", err)
+		}
+	})
+}
+
+// TestNativeValueUnsupportedKind covers the default branch of NativeValue.
+func TestNativeValueUnsupportedKind(t *testing.T) {
+	// An MxValue with no oneof Kind set and IsNull false hits the default.
+	_, err := NativeValue(&pb.MxValue{})
+	if err == nil {
+		t.Fatal("expected an error for an MxValue with no kind set")
+	}
+	if !strings.Contains(err.Error(), "unsupported value kind") {
+		t.Fatalf("unexpected error text: %v", err)
+	}
+}
+
+// --- Client.Go-005: dial migration -----------------------------------------
+
+// TestDialFailsFastWhenGatewayUnreachable confirms that after the migration to
+// grpc.NewClient the DialTimeout-bounded readiness probe still fails fast (and
+// wraps the failure in *GatewayError) when the gateway cannot be reached.
+func TestDialFailsFastWhenGatewayUnreachable(t *testing.T) {
+	dialer := func(ctx context.Context, _ string) (net.Conn, error) {
+		return nil, errors.New("connection refused")
+	}
+	start := time.Now()
+	client, err := Dial(context.Background(), Options{
+		Endpoint:    "passthrough:///unreachable",
+		APIKey:      "k",
+		Plaintext:   true,
+		DialTimeout: 500 * time.Millisecond,
+		DialOptions: []grpc.DialOption{grpc.WithContextDialer(dialer)},
+	})
+	elapsed := time.Since(start)
+	if err == nil {
+		client.Close()
+		t.Fatal("expected Dial to fail for an unreachable gateway")
+	}
+	var gwErr *GatewayError
+	if !errors.As(err, &gwErr) || gwErr.Op != "dial" {
+		t.Fatalf("expected a *GatewayError with Op=dial, got %#v", err)
+	}
+	if elapsed > 5*time.Second {
+		t.Fatalf("Dial did not honor DialTimeout: took %v", elapsed)
+	}
+}
+
+// TestDialReadinessProbeReachesReady confirms the readiness probe succeeds
+// against a live (bufconn) gateway, i.e. the lazy grpc.NewClient connection is
+// driven to Ready before Dial returns.
+func TestDialReadinessProbeReachesReady(t *testing.T) {
+	client, cleanup := newBufconnClient(t, &fakeGatewayServer{
+		openReply: &pb.OpenSessionReply{},
+	})
+	defer cleanup()
+	if client == nil {
+		t.Fatal("expected a connected client")
+	}
+}
+
+// --- Client.Go-006: error taxonomy ----------------------------------------
+
+// TestGatewayErrorCode confirms GatewayError.Code surfaces the wrapped gRPC
+// status code without the caller unwrapping it.
+func TestGatewayErrorCode(t *testing.T) {
+	var nilErr *GatewayError
+	if got := nilErr.Code(); got != codes.OK {
+		t.Fatalf("nil GatewayError.Code() = %v, want OK", got)
+	}
+
+	gwErr := &GatewayError{Op: "invoke", Err: status.Error(codes.Unavailable, "down")}
+	if got := gwErr.Code(); got != codes.Unavailable {
+		t.Fatalf("GatewayError.Code() = %v, want Unavailable", got)
+	}
+
+	plain := &GatewayError{Op: "dial", Err: errors.New("boom")}
+	if got := plain.Code(); got != codes.Unknown {
+		t.Fatalf("GatewayError.Code() for a non-status error = %v, want Unknown", got)
+	}
+}
+
+// TestIsTransient verifies the transient/permanent classification including
+// the unwrap-through-GatewayError path.
+func TestIsTransient(t *testing.T) {
+	tests := []struct {
+		name string
+		err  error
+		want bool
+	}{
+		{name: "nil", err: nil, want: false},
+		{name: "unavailable wrapped", err: &GatewayError{Op: "invoke", Err: status.Error(codes.Unavailable, "x")}, want: true},
+		{name: "deadline wrapped", err: &GatewayError{Op: "invoke", Err: status.Error(codes.DeadlineExceeded, "x")}, want: true},
+		{name: "resource exhausted", err: &GatewayError{Err: status.Error(codes.ResourceExhausted, "x")}, want: true},
+		{name: "unauthenticated permanent", err: &GatewayError{Err: status.Error(codes.Unauthenticated, "x")}, want: false},
+		{name: "invalid argument permanent", err: &GatewayError{Err: status.Error(codes.InvalidArgument, "x")}, want: false},
+		{name: "bare status unavailable", err: status.Error(codes.Unavailable, "x"), want: true},
+		{name: "plain error", err: errors.New("nope"), want: false},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := IsTransient(tt.err); got != tt.want {
+				t.Fatalf("IsTransient(%v) = %v, want %v", tt.err, got, tt.want)
+			}
+		})
+	}
+}
+
+// --- Client.Go-007: correlation id fallback --------------------------------
+
+// TestNewCorrelationIDUsesRandEntropy confirms the happy path yields a
+// 32-hex-character id.
+func TestNewCorrelationIDUsesRandEntropy(t *testing.T) {
+	id := newCorrelationID()
+	if len(id) != 32 {
+		t.Fatalf("expected a 32-char hex id, got %q (len %d)", id, len(id))
+	}
+}
+
+// TestNewCorrelationIDFallsBackOnRandFailure reproduces Client.Go-007: when
+// crypto/rand fails, newCorrelationID must not return an empty string but a
+// unique, non-empty fallback id so the command stays traceable.
+func TestNewCorrelationIDFallsBackOnRandFailure(t *testing.T) {
+	original := randRead
+	randRead = func([]byte) (int, error) { return 0, errors.New("entropy unavailable") }
+	defer func() { randRead = original }()
+
+	first := newCorrelationID()
+	second := newCorrelationID()
+
+	if first == "" || second == "" {
+		t.Fatal("newCorrelationID returned an empty id on rand failure")
+	}
+	if !strings.HasPrefix(first, "fallback-") {
+		t.Fatalf("expected a fallback- prefixed id, got %q", first)
+	}
+	if first == second {
+		t.Fatalf("fallback correlation ids must be unique, got %q twice", first)
+	}
+}

clients/go/mxgateway/errors.go

@@ -5,6 +5,8 @@ import (
 	"fmt"
 
 	pb "gitea.dohertylan.com/dohertj2/mxaccessgw/clients/go/internal/generated"
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/status"
 )
 
 // ErrEventBufferOverflow is the terminal error delivered on the compatibility
@@ -42,6 +44,45 @@ func (e *GatewayError) Unwrap() error {
 	return e.Err
 }
 
+// Code returns the gRPC status code of the wrapped transport error. It returns
+// codes.OK when the error is nil and codes.Unknown when the wrapped error does
+// not carry a gRPC status. Callers can use it to write retry, timeout, and
+// auth handling without manually unwrapping and re-parsing the error.
+func (e *GatewayError) Code() codes.Code {
+	if e == nil || e.Err == nil {
+		return codes.OK
+	}
+	return status.Code(e.Err)
+}
+
+// IsTransient reports whether err is a transport failure that may succeed on
+// retry — for example a gateway that is briefly Unavailable or a call that
+// hit a DeadlineExceeded. Permanent failures (Unauthenticated, PermissionDenied,
+// InvalidArgument, NotFound, and similar) return false. It unwraps through
+// *GatewayError and any other error chain carrying a gRPC status, so callers
+// do not need to call status.Code themselves.
+func IsTransient(err error) bool {
+	if err == nil {
+		return false
+	}
+	switch transientCode(err) {
+	case codes.Unavailable, codes.DeadlineExceeded, codes.ResourceExhausted, codes.Aborted:
+		return true
+	default:
+		return false
+	}
+}
+
+// transientCode extracts a gRPC status code from err, preferring a wrapped
+// *GatewayError's Code and otherwise falling back to status.Code on the chain.
+func transientCode(err error) codes.Code {
+	var gatewayErr *GatewayError
+	if errors.As(err, &gatewayErr) {
+		return gatewayErr.Code()
+	}
+	return status.Code(err)
+}
+
 // CommandError reports a non-OK gateway protocol status and keeps the raw
 // command reply when one exists.
 type CommandError struct {

clients/go/mxgateway/galaxy.go

@@ -2,7 +2,6 @@ package mxgateway
 
 import (
 	"context"
-	"errors"
 	"io"
 	"time"
 
@@ -56,39 +55,13 @@ type GalaxyClient struct {
 
 // DialGalaxy opens a gRPC connection to the gateway for the Galaxy Repository
 // service. It applies the same authentication metadata, transport security,
-// and dial-timeout behavior as Dial.
+// lazy connection, and DialTimeout-bounded readiness probe as Dial.
 func DialGalaxy(ctx context.Context, opts Options) (*GalaxyClient, error) {
-	if opts.Endpoint == "" {
+	conn, err := dial(ctx, opts)
-		return nil, errors.New("mxgateway: endpoint is required")
-	}
-
-	dialCtx := ctx
-	cancel := func() {}
-	if opts.DialTimeout > 0 {
-		dialCtx, cancel = context.WithTimeout(ctx, opts.DialTimeout)
-	} else if _, ok := ctx.Deadline(); !ok {
-		dialCtx, cancel = context.WithTimeout(ctx, defaultDialTimeout)
-	}
-	defer cancel()
-
-	transportCredentials, err := resolveTransportCredentials(opts)
 	if err != nil {
 		return nil, err
 	}
 
-	dialOptions := []grpc.DialOption{
-		grpc.WithTransportCredentials(transportCredentials),
-		grpc.WithUnaryInterceptor(unaryAuthInterceptor(opts.APIKey)),
-		grpc.WithStreamInterceptor(streamAuthInterceptor(opts.APIKey)),
-		grpc.WithBlock(),
-	}
-	dialOptions = append(dialOptions, opts.DialOptions...)
-
-	conn, err := grpc.DialContext(dialCtx, opts.Endpoint, dialOptions...)
-	if err != nil {
-		return nil, &GatewayError{Op: "dial", Err: err}
-	}
-
 	return NewGalaxyClient(conn, opts), nil
 }
 
@@ -239,18 +212,5 @@ func (c *GalaxyClient) Close() error {
 }
 
 func (c *GalaxyClient) callContext(ctx context.Context) (context.Context, context.CancelFunc) {
-	timeout := c.opts.CallTimeout
+	return callContext(ctx, c.opts.CallTimeout)
-	if timeout == 0 {
-		timeout = defaultCallTimeout
-	}
-	if timeout < 0 {
-		return ctx, func() {}
-	}
-	if deadline, ok := ctx.Deadline(); ok {
-		timeoutDeadline := time.Now().Add(timeout)
-		if deadline.Before(timeoutDeadline) {
-			return ctx, func() {}
-		}
-	}
-	return context.WithTimeout(ctx, timeout)
 }

clients/go/mxgateway/galaxy_test.go

@@ -55,8 +55,8 @@ func TestGalaxyGetLastDeployTimeReturnsTimestampWhenPresent(t *testing.T) {
 	want := time.Date(2026, 4, 28, 12, 34, 56, 0, time.UTC)
 	fake := &fakeGalaxyServer{
 		deployReply: &pb.GetLastDeployTimeReply{
-			Present:           true,
+			Present:          true,
-			TimeOfLastDeploy:  timestamppb.New(want),
+			TimeOfLastDeploy: timestamppb.New(want),
 		},
 	}
 	client, cleanup := newGalaxyBufconnClient(t, fake)
@@ -348,8 +348,10 @@ func newGalaxyBufconnClient(t *testing.T, fake *fakeGalaxyServer) (*GalaxyClient
 	dialer := func(ctx context.Context, _ string) (net.Conn, error) {
 		return listener.DialContext(ctx)
 	}
+	// grpc.NewClient defaults to the dns scheme; use passthrough so the
+	// bufconn fake target reaches the context dialer unresolved.
 	client, err := DialGalaxy(context.Background(), Options{
-		Endpoint:  "bufnet",
+		Endpoint:  "passthrough:///bufnet",
 		APIKey:    "test-api-key",
 		Plaintext: true,
 		DialOptions: []grpc.DialOption{

clients/go/mxgateway/session.go

@@ -8,6 +8,8 @@ import (
 	"fmt"
 	"io"
 	"sync"
+	"sync/atomic"
+	"time"
 
 	pb "gitea.dohertylan.com/dohertj2/mxaccessgw/clients/go/internal/generated"
 	"google.golang.org/grpc/codes"
@@ -547,10 +549,25 @@ func (s *Session) invokeCommand(ctx context.Context, command *MxCommand) (*MxCom
 	})
 }
 
+// correlationIDCounter backs the deterministic fallback id used when
+// crypto/rand is unavailable, so every command still carries a unique,
+// traceable correlation id.
+var correlationIDCounter atomic.Uint64
+
+// randRead is the entropy source for newCorrelationID. It is a package
+// variable solely so tests can simulate a crypto/rand failure.
+var randRead = rand.Read
+
+// newCorrelationID returns a unique correlation id for an MxCommandRequest.
+// It prefers 16 bytes of crypto/rand entropy; if rand.Read fails (rare) it
+// falls back to a "fallback-" prefixed id built from the current time and a
+// process-wide monotonic counter rather than returning an empty string, which
+// would leave the command untraceable in gateway logs.
 func newCorrelationID() string {
 	var buffer [16]byte
-	if _, err := rand.Read(buffer[:]); err != nil {
+	if _, err := randRead(buffer[:]); err != nil {
-		return ""
+		return fmt.Sprintf("fallback-%x-%x",
+			time.Now().UnixNano(), correlationIDCounter.Add(1))
 	}
 	return hex.EncodeToString(buffer[:])
 }

code-reviews/Client.Go/findings.md

@@ -7,7 +7,7 @@
 | Review date | 2026-05-18 |
 | Commit reviewed | `3cc53a8` |
 | Status | Reviewed |
-| Open findings | 7 |
+| Open findings | 0 |
 
 ## Checklist coverage
 
@@ -78,13 +78,13 @@
 | Severity | Low |
 | Category | mxaccessgw conventions |
 | Location | `clients/go/mxgateway/alarms_test.go:153-154`, `clients/go/mxgateway/galaxy_test.go:58-59` |
-| Status | Open |
+| Status | Resolved |
 
 **Description:** `gofmt -l` flags `alarms_test.go` and `galaxy_test.go` for misaligned struct-literal field padding. The Go client README lists `gofmt` as part of the workflow and the repo enforces style; unformatted committed code breaks `gofmt`-gated checks and CI.
 
 **Recommendation:** Run `gofmt -w mxgateway/alarms_test.go mxgateway/galaxy_test.go`.
 
-**Resolution:** _(open)_
+**Resolution:** Resolved 2026-05-18: confirmed `gofmt -l .` flagged both files for misaligned struct-literal padding. Ran `gofmt -w` on `mxgateway/alarms_test.go` and `mxgateway/galaxy_test.go`; `gofmt -l .` is now clean for the whole module.
 
 ### Client.Go-005
 
@@ -93,13 +93,13 @@
 | Severity | Low |
 | Category | Design-document adherence |
 | Location | `clients/go/mxgateway/client.go:64,68`, `clients/go/mxgateway/galaxy.go:83,87` |
-| Status | Open |
+| Status | Resolved |
 
 **Description:** The client uses `grpc.DialContext` with `grpc.WithBlock()`. In current grpc-go both are deprecated in favour of `grpc.NewClient` (lazy connection). `WithBlock` also changes failure semantics: a transient gateway-unavailable at dial time becomes a hard `Dial` error rather than a connection that recovers when the gateway comes up, working against the design doc's resilience intent.
 
 **Recommendation:** Migrate to `grpc.NewClient`; if a fail-fast connect probe is still wanted, do an explicit readiness wait bounded by `DialTimeout`, and update the doc comment.
 
-**Resolution:** _(open)_
+**Resolution:** Resolved 2026-05-18: confirmed `Dial`/`DialGalaxy` used the deprecated `grpc.DialContext` + `grpc.WithBlock` pair. Migrated both to the shared `dial(ctx, opts)` helper, which now builds a lazy connection with `grpc.NewClient` and runs an explicit `waitForReady` readiness probe (`Connect` + `WaitForStateChange` until `connectivity.Ready`) bounded by `DialTimeout` — preserving fail-fast behavior while letting an otherwise lazy connection recover when the gateway is briefly down. Note: `grpc.NewClient` defaults the target scheme to `dns`, so the bufconn test harnesses (`client_session_test.go`, `alarms_test.go`, `galaxy_test.go`) were updated to use `passthrough:///bufnet` so the fake target reaches the context dialer. New tests `TestDialFailsFastWhenGatewayUnreachable` and `TestDialReadinessProbeReachesReady` cover the probe; `go vet` reports no deprecation. `clients/go/README.md` documents the lazy-connect + readiness-probe semantics.
 
 ### Client.Go-006
 
@@ -108,13 +108,13 @@
 | Severity | Low |
 | Category | Error handling & resilience |
 | Location | `clients/go/mxgateway/errors.go:9-130` |
-| Status | Open |
+| Status | Resolved |
 
 **Description:** `docs/ClientLibrariesDesign.md` recommends a high-level error taxonomy (`TransportError`, `AuthenticationError`, `TimeoutError`, etc.). The Go client collapses all transport/gRPC failures into a single `GatewayError` with no way to classify transient (`Unavailable`, `DeadlineExceeded`) vs permanent (`Unauthenticated`, `InvalidArgument`) without manually unwrapping and calling `status.Code`.
 
 **Recommendation:** Add a helper (e.g. `IsTransient(err) bool`) or expose the gRPC `codes.Code` on `GatewayError`, so retry/timeout/auth handling can be written without re-parsing the wrapped error.
 
-**Resolution:** _(open)_
+**Resolution:** Resolved 2026-05-18: implemented the recommended classification surface in `errors.go` rather than a full parallel type hierarchy (the existing `GatewayError`/`CommandError`/`MxAccessError` chain already separates transport from protocol from MXAccess failures). Added `GatewayError.Code()` (returns the wrapped gRPC `codes.Code`, `OK` for nil, `Unknown` for a non-status error) and the free function `IsTransient(err error) bool`, which unwraps through `*GatewayError` and any gRPC-status chain and reports `true` for `Unavailable`, `DeadlineExceeded`, `ResourceExhausted`, and `Aborted`. Tests `TestGatewayErrorCode` and `TestIsTransient` cover the matrix; `clients/go/README.md` documents both for retry/timeout/auth handling.
 
 ### Client.Go-007
 
@@ -123,13 +123,13 @@
 | Severity | Low |
 | Category | Correctness & logic bugs |
 | Location | `clients/go/mxgateway/session.go:526-532` |
-| Status | Open |
+| Status | Resolved |
 
 **Description:** `newCorrelationID` returns an empty string when `crypto/rand.Read` fails, silently producing an `MxCommandRequest` with no correlation id. `rand.Read` failure is rare, but the failure mode (untraceable command, no error surfaced) is worse than failing loud, and the empty-id path is untested.
 
 **Recommendation:** Either propagate the error up through `invokeCommand`, or fall back to a time/counter-based id rather than an empty string.
 
-**Resolution:** _(open)_
+**Resolution:** Resolved 2026-05-18: confirmed `newCorrelationID` returned `""` on a `rand.Read` failure. It now falls back to a non-empty `"fallback-<unixnano>-<counter>"` id built from `time.Now().UnixNano()` and a process-wide `atomic.Uint64` monotonic counter, so every command stays traceable even without entropy. The `crypto/rand` call was routed through a `randRead` package variable so the failure path is testable; `TestNewCorrelationIDFallsBackOnRandFailure` simulates a `rand.Read` failure and asserts the fallback id is non-empty, `fallback-` prefixed, and unique, and `TestNewCorrelationIDUsesRandEntropy` pins the happy path.
 
 ### Client.Go-008
 
@@ -138,13 +138,13 @@
 | Severity | Low |
 | Category | Testing coverage |
 | Location | `clients/go/mxgateway/` (test files) |
-| Status | Open |
+| Status | Resolved |
 
 **Description:** Several critical paths are untested: TLS credential resolution in `resolveTransportCredentials` (only the `Plaintext` path is exercised); the `callContext` deadline-shortening logic (`client.go:198-204`) including the negative-timeout disable case; and `NativeValue`/`NativeArray` for the array, raw-bytes, null, and unsupported-kind branches.
 
 **Recommendation:** Add unit tests for `resolveTransportCredentials` precedence, `callContext` deadline arithmetic, and `NativeValue`/`NativeArray` round-trips for every kind.
 
-**Resolution:** _(open)_
+**Resolution:** Resolved 2026-05-18: added `clients/go/mxgateway/coverage_test.go`. `TestResolveTransportCredentialsPrecedence` exercises every branch (explicit `TransportCredentials`, `Plaintext`, missing `CACertFile` error, `TLSConfig` + `ServerNameOverride`, default TLS floor) and `TestResolveTransportCredentialsDoesNotMutateTLSConfig` confirms the supplied `*tls.Config` is cloned. `TestCallContextDeadlineArithmetic` covers zero/default, negative-disable, positive timeout, caller-deadline-sooner-kept, and caller-deadline-later-shortened. `TestNativeValueEdgeKinds`, `TestNativeArrayEdgeKinds`, and `TestNativeValueUnsupportedKind` cover the null, raw-bytes (including the no-alias copy), array, timestamp-with-nil, and unsupported-kind branches.
 
 ### Client.Go-009
 
@@ -153,13 +153,13 @@
 | Severity | Low |
 | Category | Code organization & conventions |
 | Location | `clients/go/mxgateway/galaxy.go:60-93,241-256`, `clients/go/mxgateway/client.go:41-74,190-205` |
-| Status | Open |
+| Status | Resolved |
 
 **Description:** `DialGalaxy`/`Dial` and `GalaxyClient.callContext`/`Client.callContext` are near-identical duplicates (dial-context setup, credential resolution, dial-option assembly, deadline arithmetic). A fix to one (e.g. the Client.Go-005 dial migration) must be applied twice and can drift.
 
 **Recommendation:** Extract a shared unexported `dial(ctx, opts)` and a free `callContext(opts, ctx)` function, and have both client constructors call them.
 
-**Resolution:** _(open)_
+**Resolution:** Resolved 2026-05-18: extracted the shared unexported `dial(ctx, opts) (*grpc.ClientConn, error)` (credential resolution, dial-option assembly, `grpc.NewClient`, readiness probe) and the free `callContext(ctx, callTimeout) (context.Context, context.CancelFunc)` into `client.go`. `Dial`/`DialGalaxy` and both `(*Client).callContext`/`(*GalaxyClient).callContext` methods now delegate to them; the duplicated dial and deadline code in `galaxy.go` was removed (its now-unused `errors` import dropped). This was done together with the Client.Go-005 migration so the `grpc.NewClient` change lives in exactly one place.
 
 ### Client.Go-010
 
@@ -168,10 +168,10 @@
 | Severity | Low |
 | Category | Documentation & comments |
 | Location | `clients/go/mxgateway/client.go:39-40` |
-| Status | Open |
+| Status | Resolved |
 
 **Description:** The `Dial` doc comment states it configures "blocking dial cancellation from ctx." This describes the deprecated `WithBlock` behaviour; once Client.Go-005 is addressed the comment is misleading about how connection establishment and cancellation work.
 
 **Recommendation:** Reword to describe the actual connect/timeout semantics after resolving Client.Go-005, and clarify that `DialTimeout` bounds the initial connect attempt.
 
-**Resolution:** _(open)_
+**Resolution:** Resolved 2026-05-18: alongside the Client.Go-005 migration, the `Dial` doc comment was rewritten to describe the lazy `grpc.NewClient` connection, the `DialTimeout`-bounded (default 10s, or ctx deadline when sooner) readiness probe, that a briefly-unavailable gateway recovers instead of producing a hard error, and that cancelling `ctx` aborts the probe. `DialGalaxy` and the new `dial`/`waitForReady`/`callContext` helpers carry matching doc comments.