diff --git a/pkg/client/bass_integration_test.go b/pkg/client/bass_integration_test.go
index 94edd94..2b231f6 100644
--- a/pkg/client/bass_integration_test.go
+++ b/pkg/client/bass_integration_test.go
@@ -6,6 +6,7 @@ import (
 	"time"
 
 	"github.com/gesellix/bose-soundtouch/pkg/models"
+	"github.com/gesellix/bose-soundtouch/pkg/speaker"
 )
 
 // Integration tests for bass control functionality
@@ -426,7 +427,7 @@ func BenchmarkClient_Bass_Integration(b *testing.B) {
 // This is a simple version for test use
 func parseBassHostPort(hostPort string) (string, int) {
 	if !containsSubstring(hostPort, ":") {
-		return hostPort, defaultSoundTouchPort
+		return hostPort, speaker.HTTPPort
 	}
 
 	// Simple parsing - in real use, we'd use net.SplitHostPort
@@ -448,7 +449,7 @@ func parseBassHostPort(hostPort string) (string, int) {
 
 	if len(parts) == 2 {
 		// Try to parse port
-		port := defaultSoundTouchPort
+		port := speaker.HTTPPort
 		portStr := parts[1]
 		portInt := 0
 
@@ -468,5 +469,5 @@ func parseBassHostPort(hostPort string) (string, int) {
 		return parts[0], port
 	}
 
-	return hostPort, defaultSoundTouchPort
+	return hostPort, speaker.HTTPPort
 }
diff --git a/pkg/client/source_selection_integration_test.go b/pkg/client/source_selection_integration_test.go
index de7b6b5..77d6a25 100644
--- a/pkg/client/source_selection_integration_test.go
+++ b/pkg/client/source_selection_integration_test.go
@@ -4,6 +4,8 @@ import (
 	"os"
 	"testing"
 	"time"
+
+	"github.com/gesellix/bose-soundtouch/pkg/speaker"
 )
 
 // Integration tests for source selection functionality
@@ -386,7 +388,7 @@ func BenchmarkClient_SelectSource_Integration(b *testing.B) {
 // This is a simple version for test use
 func parseHostPort(hostPort string) (string, int) {
 	if !containsSubstring(hostPort, ":") {
-		return hostPort, defaultSoundTouchPort
+		return hostPort, speaker.HTTPPort
 	}
 
 	// Simple parsing - in real use, we'd use net.SplitHostPort
@@ -408,7 +410,7 @@ func parseHostPort(hostPort string) (string, int) {
 
 	if len(parts) == 2 {
 		// Try to parse port
-		port := defaultSoundTouchPort
+		port := speaker.HTTPPort
 		portStr := parts[1]
 		portInt := 0
 
@@ -428,5 +430,5 @@ func parseHostPort(hostPort string) (string, int) {
 		return parts[0], port
 	}
 
-	return hostPort, defaultSoundTouchPort
+	return hostPort, speaker.HTTPPort
 }
diff --git a/pkg/service/constants/constants.go b/pkg/service/constants/constants.go
index 7bf1df4..ca52eb4 100644
--- a/pkg/service/constants/constants.go
+++ b/pkg/service/constants/constants.go
@@ -299,11 +299,10 @@ const (
 	RecentsFile    = "Recents.xml"
 	SourcesFile    = "Sources.xml"
 
-	SpeakerHTTPPort            = 8090
-	SpeakerDeviceInfoPath      = "/info"
-	SpeakerRecentsPath         = "/recents"
-	SpeakerPresetsPath         = "/presets"
-	SpeakerSourcesFileLocation = "/mnt/nv/BoseApp-Persistence/1/Sources.xml"
+	// Speaker-protocol constants (HTTP port, paths, on-device file
+	// locations) moved to github.com/gesellix/bose-soundtouch/pkg/speaker
+	// so the client library and CLI can share them without depending on
+	// the service package.
 
 	// DateStr is the hardcoded date used in many Bose XML responses
 	DateStr = "2012-09-19T12:43:00.000+00:00"
diff --git a/pkg/service/constants/constants_test.go b/pkg/service/constants/constants_test.go
index 2b0e8e2..dd552fb 100644
--- a/pkg/service/constants/constants_test.go
+++ b/pkg/service/constants/constants_test.go
@@ -9,10 +9,6 @@ func TestConstants(t *testing.T) {
 		t.Error("DateStr should not be empty")
 	}
 
-	if SpeakerHTTPPort != 8090 {
-		t.Errorf("Expected SpeakerHTTPPort 8090, got %d", SpeakerHTTPPort)
-	}
-
 	if len(GetProviders()) == 0 {
 		t.Error("Providers should not be empty")
 	}
diff --git a/pkg/speaker/speaker.go b/pkg/speaker/speaker.go
new file mode 100644
index 0000000..5fbfd56
--- /dev/null
+++ b/pkg/speaker/speaker.go
@@ -0,0 +1,29 @@
+// Package speaker holds protocol-level constants for the Bose SoundTouch
+// speaker's local API surface: the well-known HTTP port, the request paths
+// exposed by every device, and the on-device file locations the migration
+// flow needs to know about.
+//
+// This package is intentionally a leaf with no internal dependencies, so
+// any layer can import it (client library, service, CLI, tests) without
+// introducing a cycle or a cross-topic edge. Anything speaker-shaped that
+// would otherwise be duplicated between packages belongs here.
+package speaker
+
+// HTTPPort is the well-known port the SoundTouch device exposes its local
+// API on (e.g. /info, /presets, /group).
+const HTTPPort = 8090
+
+// Well-known HTTP paths the SoundTouch device serves on HTTPPort.
+const (
+	DeviceInfoPath = "/info"
+	PresetsPath    = "/presets"
+	RecentsPath    = "/recents"
+)
+
+// On-device filesystem paths that the migration/sync flow needs to read or
+// write over SSH. These live in the device's persistence area and are not
+// part of the HTTP surface.
+const (
+	SourcesFileLocation      = "/mnt/nv/BoseApp-Persistence/1/Sources.xml"
+	GroupServiceFileLocation = "/mnt/nv/BoseApp-Persistence/1/GroupService.xml"
+)
diff --git a/pkg/speaker/speaker_test.go b/pkg/speaker/speaker_test.go
new file mode 100644
index 0000000..0606597
--- /dev/null
+++ b/pkg/speaker/speaker_test.go
@@ -0,0 +1,25 @@
+package speaker
+
+import "testing"
+
+// Sanity-check the well-known values — a wrong number here would silently
+// break every transport and is cheap to guard against.
+func TestSpeakerConstants(t *testing.T) {
+	if HTTPPort != 8090 {
+		t.Errorf("HTTPPort = %d, want 8090", HTTPPort)
+	}
+
+	cases := map[string]string{
+		"DeviceInfoPath":           DeviceInfoPath,
+		"PresetsPath":              PresetsPath,
+		"RecentsPath":              RecentsPath,
+		"SourcesFileLocation":      SourcesFileLocation,
+		"GroupServiceFileLocation": GroupServiceFileLocation,
+	}
+
+	for name, val := range cases {
+		if val == "" {
+			t.Errorf("%s is empty", name)
+		}
+	}
+}