fix: preserve partial batch property results

device.go

@@ -747,6 +747,7 @@ func (device *Device) GetMany(ctx context.Context, names []string) ([]DeviceProp
 			return nil, err
 		}
 		byIdentity := make(map[propertyIdentity]PropertyResult, len(chunkResults))
+		duplicateIdentities := make(map[propertyIdentity]struct{})
 		requested := make(map[propertyIdentity]struct{}, end-start)
 		for _, request := range requests[start:end] {
 			requested[propertyIdentity{did: request.DID, siid: request.SIID, piid: request.PIID}] = struct{}{}
@@ -757,17 +758,30 @@ func (device *Device) GetMany(ctx context.Context, names []string) ([]DeviceProp
 				return nil, fmt.Errorf("get properties protocol error: unexpected identity (%s,%d,%d)", result.DID, result.SIID, result.PIID)
 			}
 			if _, duplicate := byIdentity[identity]; duplicate {
-				return nil, fmt.Errorf("get properties protocol error: duplicate identity (%s,%d,%d)", result.DID, result.SIID, result.PIID)
+				duplicateIdentities[identity] = struct{}{}
+				continue
 			}
 			byIdentity[identity] = result
 		}
 		for index, request := range requests[start:end] {
 			identity := propertyIdentity{did: request.DID, siid: request.SIID, piid: request.PIID}
+			name := names[start+index]
+			if _, duplicate := duplicateIdentities[identity]; duplicate {
+				results[start+index] = DevicePropertyResult{
+					Name: name,
+					Err:  fmt.Errorf("get properties protocol error: duplicate identity (%s,%d,%d)", request.DID, request.SIID, request.PIID),
+				}
+				continue
+			}
 			result, ok := byIdentity[identity]
 			if !ok {
-				return nil, fmt.Errorf("get properties protocol error: missing identity (%s,%d,%d)", request.DID, request.SIID, request.PIID)
+				results[start+index] = DevicePropertyResult{
+					Name: name,
+					Err:  fmt.Errorf("get properties protocol error: missing identity (%s,%d,%d)", request.DID, request.SIID, request.PIID),
 				}
-			results[start+index] = DevicePropertyResult{Name: names[start+index], Value: result.Value, Code: result.Code}
+				continue
+			}
+			results[start+index] = DevicePropertyResult{Name: name, Value: result.Value, Code: result.Code}
 		}
 	}
 	if err := device.wait(ctx); err != nil {

device_test.go

@@ -625,26 +625,51 @@ func TestDeviceGetManyMatchesIdentityAndPreservesBusinessErrors(t *testing.T) {
 	}
 }
 
-func TestDeviceGetManyRejectsInvalidResponseIdentities(t *testing.T) {
+func TestDeviceGetManyPreservesPartialResultsForInvalidResponseIdentities(t *testing.T) {
 	tests := []struct {
 		name     string
 		response string
+		wantErrs []string
 	}{
-		{name: "missing", response: `[{"did":"a","siid":2,"piid":1,"value":true,"code":0}]`},
+		{name: "missing", response: `[{"did":"a","siid":2,"piid":1,"value":true,"code":0}]`, wantErrs: []string{"", "missing identity"}},
-		{name: "duplicate", response: `[{"did":"a","siid":2,"piid":1,"value":true,"code":0},{"did":"a","siid":2,"piid":1,"value":false,"code":0}]`},
+		{name: "duplicate and missing", response: `[{"did":"a","siid":2,"piid":1,"value":true,"code":0},{"did":"a","siid":2,"piid":1,"value":false,"code":0}]`, wantErrs: []string{"duplicate identity", "missing identity"}},
-		{name: "extra", response: `[{"did":"a","siid":2,"piid":1,"value":true,"code":0},{"did":"a","siid":2,"piid":2,"value":5,"code":0},{"did":"other","siid":9,"piid":9,"value":1,"code":0}]`},
 	}
 	for _, test := range tests {
 		t.Run(test.name, func(t *testing.T) {
 			device := fixtureDeviceWithResults(t, []string{test.response}, 0)
 			results, err := device.GetMany(context.Background(), []string{"power", "brightness"})
-			if err == nil || results != nil || !strings.Contains(err.Error(), "protocol") {
+			if err != nil || len(results) != 2 {
-				t.Fatalf("GetMany() = %#v, %v, want nil protocol error", results, err)
+				t.Fatalf("GetMany() = %#v, %v", results, err)
+			}
+			for index, wantErr := range test.wantErrs {
+				if results[index].Name != []string{"power", "brightness"}[index] {
+					t.Fatalf("result %d name = %q", index, results[index].Name)
+				}
+				if wantErr == "" {
+					if results[index].Err != nil || results[index].Value != true {
+						t.Fatalf("result %d = %#v, want successful power result", index, results[index])
+					}
+				} else if results[index].Err == nil || !strings.Contains(results[index].Err.Error(), wantErr) {
+					t.Fatalf("result %d error = %v, want %q", index, results[index].Err, wantErr)
+				}
 			}
 		})
 	}
 }
 
+func TestDeviceGetManyRejectsExtraResponseIdentity(t *testing.T) {
+	device := fixtureDeviceWithResults(t, []string{`[
+		{"did":"a","siid":2,"piid":1,"value":true,"code":0},
+		{"did":"a","siid":2,"piid":2,"value":5,"code":0},
+		{"did":"other","siid":9,"piid":9,"value":1,"code":0}
+	]`}, 0)
+
+	results, err := device.GetMany(context.Background(), []string{"power", "brightness"})
+	if err == nil || results != nil || !strings.Contains(err.Error(), "protocol") {
+		t.Fatalf("GetMany() = %#v, %v, want nil protocol error", results, err)
+	}
+}
+
 func TestDeviceGetManyValidatesBeforeNetwork(t *testing.T) {
 	device, testServer := fixtureDeviceWithServer(t, nil)
 	tests := [][]string{{"power", "power"}, {"power", "missing"}, {"power", "write-only"}}
@@ -692,6 +717,20 @@ func TestDeviceGetManyWaitsOnceAfterAllChunks(t *testing.T) {
 	}
 }
 
+func TestDeviceGetManyWaitsOnceWithPartialProtocolErrors(t *testing.T) {
+	device := fixtureDeviceWithResults(t, []string{`[{"did":"a","siid":2,"piid":1,"value":true,"code":0}]`}, 40*time.Millisecond)
+
+	started := time.Now()
+	results, err := device.GetMany(context.Background(), []string{"power", "brightness"})
+	elapsed := time.Since(started)
+	if err != nil || len(results) != 2 || results[1].Err == nil {
+		t.Fatalf("GetMany() = %#v, %v", results, err)
+	}
+	if elapsed < 30*time.Millisecond || elapsed >= 75*time.Millisecond {
+		t.Fatalf("GetMany() delay = %v, want one approximately 40ms wait", elapsed)
+	}
+}
+
 func batchPropertyFixture(count int) (map[string]PropertySpec, []string) {
 	properties := make(map[string]PropertySpec, count)
 	names := make([]string, count)

types.go

@@ -163,6 +163,7 @@ type DevicePropertyResult struct {
 	Name  string
 	Value any
 	Code  int
+	Err   error `json:"-"`
 }
 
 type ActionRequest struct {