feat(requestlog): report speculation and build progress to requests

api/submitqueue/gateway/proto/gateway.proto

@@ -170,12 +170,18 @@ message GetRequestHistoryByIDRequest {
 message HistoryEvent {
     // Time the request-log entry was created, in Unix milliseconds.
     int64 timestamp_ms = 1;
-    // Customer-friendly request status recorded by the event.
+    // Customer-friendly request status recorded by the event. Set only when type is "status".
     string status = 2;
     // Error message associated with the event. Empty when absent.
     string last_error = 3;
     // Display and debugging metadata associated with this event. Each lifecycle event carries its own values.
     map<string, string> metadata = 4;
+    // What this entry records: "status" when the request reached a position in the pipeline,
+    // "event" when something happened while it sat at one. Exactly one of status and event is set.
+    string type = 5;
+    // Occurrence recorded by the entry, e.g. a build starting or finishing. Set only when type is "event".
+    // A request records many of these — one per build — and they never change its current status.
+    string event = 6;
 }
 
 // GetRequestHistoryByIDResponse contains all retained events for one request.

service/submitqueue/gateway/server/mapper/request_history.go

@@ -30,12 +30,18 @@ func ProtoToGetRequestHistoryByChangeURIRequest(req *pb.GetRequestHistoryByChang
 }
 
 // HistoryEventsToProto maps retained request-log events to wire history events.
+//
+// Status and Event are mutually exclusive, mirroring the entry itself: a client
+// reading the timeline can render a position and an occurrence differently
+// without having to know which values belong to which vocabulary.
 func HistoryEventsToProto(logs []entity.RequestLog) []*pb.HistoryEvent {
 	events := make([]*pb.HistoryEvent, len(logs))
 	for i, log := range logs {
 		events[i] = &pb.HistoryEvent{
 			TimestampMs: log.TimestampMs,
+			Type:        string(log.Type),
 			Status:      string(log.Status),
+			Event:       string(log.Event),
 			LastError:   log.LastError,
 			Metadata:    cloneStringMap(log.Metadata),
 		}