Implemented atomic session replacement.

internal/playback/session_command_test.go

@@ -114,6 +114,27 @@ func TestApplySessionCommand(t *testing.T) {
 			command: SessionCommand{Kind: CommandDisableSync},
 			want:    func() SessionConfig { c := base; c.SyncRequested = false; return c }(),
 		},
+		{
+			name:    "set complete session atomically and preserve retry",
+			current: base,
+			command: SessionCommand{
+				Kind: CommandSetSession,
+				Session: SessionConfig{
+					Video:         newVideo,
+					Audio:         newAudio,
+					SyncRequested: false,
+					Retry: RetryPolicy{
+						MaxAttempts: 99,
+					},
+				},
+			},
+			want: SessionConfig{
+				Video:         newVideo,
+				Audio:         newAudio,
+				SyncRequested: false,
+				Retry:         base.Retry,
+			},
+		},
 	}
 
 	for _, tt := range tests {
@@ -157,6 +178,17 @@ func TestApplySessionCommandFailurePreservesState(t *testing.T) {
 			ErrAudioNotConfigured,
 		},
 		{"unknown command", base, SessionCommand{Kind: 255}, ErrUnknownSessionCommand},
+		{
+			"invalid complete session",
+			base,
+			SessionCommand{
+				Kind: CommandSetSession,
+				Session: SessionConfig{
+					Video: FeedConfig{UUID: "video", Active: true},
+				},
+			},
+			ErrFeedDomainRequired,
+		},
 	}
 
 	for _, tt := range tests {