refactor(logs): update log formatting for systemd services and handle merging in the client

pkg/api/logs.go

@@ -57,14 +57,15 @@ type ServiceLogsOptions struct {
 	Machines []string
 }
 
-// ServiceLogEntry represents a single log entry from a service container.
+// ServiceLogEntry represents a single log entry from a service container or systemd service.
 type ServiceLogEntry struct {
 	// Metadata may not be set if an error occurred (Err is not nil).
 	Metadata ServiceLogEntryMetadata
 	LogEntry
 }
 
-// ServiceLogEntryMetadata contains metadata about the source of a log entry.
+// ServiceLogEntryMetadata identifies the source of a log entry.
+// For systemd service logs, ServiceID and ServiceName hold the unit name and ContainerID is empty.
 type ServiceLogEntryMetadata struct {
 	ServiceID   string
 	ServiceName string
@@ -77,7 +78,8 @@ type ServiceLogEntryMetadata struct {
 type LogEntry struct {
 	Stream    LogStreamType
 	Timestamp time.Time
-	Message   []byte
+	// Message is the raw log line as bytes terminated with a trailing newline.
+	Message []byte
 	// Err indicates that an error occurred while streaming logs from a container.
 	// Other fields are not set if Err is not nil.
 	Err error