v2.0.0: claims model - signed MMUR2 votes in a truth DB, merged view in a rebuildable cache DB; POST /api/claims, claims and merge routes, unsigned writes answer 410

internal/api/sse_events.go

@@ -112,7 +112,15 @@ func (s *Server) streamSSE(w http.ResponseWriter, r *http.Request, stream string
 		}
 		cursor = head
 	} else {
-		cursor = resolveStartCursor(ctx, store, stream, lastID, w, flusher)
+		if rebuilt := s.storage.RebuiltAt(); stream == storage.MetaEventsStream && lastID != "" && rebuilt != "" &&
+			compareStreamIDs(lastID, rebuilt) < 0 {
+			// The cache was rebuilt after this cursor: the rebuild published no
+			// per-key events, so the consumer must take a snapshot.
+			writeGap(w, flusher, lastID, rebuilt, "rebuild")
+			cursor = "0"
+		} else {
+			cursor = resolveStartCursor(ctx, store, stream, lastID, w, flusher)
+		}
 	}
 
 	lastWrite := time.Now()
@@ -256,14 +264,7 @@ func resolveStartCursor(ctx context.Context, store *kv.Store, stream, lastID str
 	}
 
 	// Cursor was trimmed. Emit a gap event so consumers that care can react.
-	gap := map[string]string{
-		"requested":  lastID,
-		"resumeFrom": oldest,
-		"reason":     "retention",
-	}
-	payload, _ := json.Marshal(gap)
-	fmt.Fprintf(w, "event: gap\ndata: %s\n\n", string(payload))
-	flusher.Flush()
+	writeGap(w, flusher, lastID, oldest, "retention")
 
 	// Return "0" so the next read picks up entries starting from the
 	// stream's true minimum — including `oldest` itself.
@@ -327,3 +328,15 @@ func parseStreamID(id string) (int64, int64) {
 	}
 	return ms, seq
 }
+
+// writeGap emits the synthetic `gap` event: the consumer's cursor cannot be
+// resumed losslessly and it should take a snapshot (Last-Event-ID: 0).
+func writeGap(w http.ResponseWriter, flusher http.Flusher, requested, resumeFrom, reason string) {
+	payload, _ := json.Marshal(map[string]string{
+		"requested":  requested,
+		"resumeFrom": resumeFrom,
+		"reason":     reason,
+	})
+	fmt.Fprintf(w, "event: gap\ndata: %s\n\n", string(payload))
+	flusher.Flush()
+}