fix(api): bound analytics backfill and reduce SQLite write amplification

packages/db/src/repositories/analytics.ts

@@ -6,6 +6,18 @@ export type StatsRollupInsert = typeof agentStatsRollups.$inferInsert
 
 /** Called inside the ingest transaction; replay checks precede this additive write. */
 export function addStatsRollups(db: Db, rows: StatsRollupInsert[]) {
+  // Backfill observations often share hour/day buckets. Merge them before
+  // UPSERT rather than rewriting the same SQLite pages per observation.
+  const merged = new Map<string, StatsRollupInsert>()
+  for (const input of rows) {
+    const key = `${input.agentId}\0${input.resolution}\0${input.bucketStart}`
+    const row = merged.get(key)
+    if (!row) { merged.set(key, { ...input }); continue }
+    for (const field of ['packetsDropped', 'packetsAccepted', 'droppedCoverageMs', 'acceptedCoverageMs', 'lostReports'] as const) row[field] = (row[field] ?? 0) + (input[field] ?? 0)
+    for (const field of ['partial', 'truncated', 'estimated'] as const) row[field] = Math.max(row[field] ?? 0, input[field] ?? 0)
+    row.unsupportedJson = JSON.stringify([...new Set([...(JSON.parse(row.unsupportedJson ?? '[]') as string[]), ...(JSON.parse(input.unsupportedJson ?? '[]') as string[])])].slice(0, 16))
+  }
+  rows = [...merged.values()]
   for (let offset = 0; offset < rows.length; offset += 100) {
     db.insert(agentStatsRollups).values(rows.slice(offset, offset + 100)).onConflictDoUpdate({
       target: [agentStatsRollups.agentId, agentStatsRollups.resolution, agentStatsRollups.bucketStart],