feat: add pastParticipants support in history sync

Surfaces past group participant data from WhatsApp history sync messages.
Previously pastParticipants was dropped during event buffering because
it was overwritten instead of accumulated across chunks.

- src/Types/Events.ts: add pastParticipants to BaileysEventMap['messaging-history.set'] and BufferedEventData.historySets
- src/Utils/event-buffer.ts: accumulate pastParticipants via spread array instead of overwriting; include in consolidateEvents output
- src/Utils/history.ts: pass item.pastParticipants in processHistoryMessage return

Refs: WhiskeySockets/Baileys#2426

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/Types/Events.ts

@@ -27,7 +27,6 @@ export type BaileysEventMap = {
 		chats: Chat[]
 		contacts: Contact[]
 		messages: WAMessage[]
-		/** Past participants for group chats (people who left/were removed). userJid is always a phone number (PN), never a LID. */
 		pastParticipants?: proto.IPastParticipants[] | null
 		isLatest?: boolean
 		progress?: number | null
@@ -187,8 +186,7 @@ export type BufferedEventData = {
 		chats: { [jid: string]: Chat }
 		contacts: { [jid: string]: Contact }
 		messages: { [uqId: string]: WAMessage }
-		/** Keyed by groupJid for O(1) deduplication across chunks */
-		pastParticipants: { [groupJid: string]: proto.IPastParticipant[] }
+		pastParticipants?: proto.IPastParticipants[]
 		empty: boolean
 		isLatest: boolean
 		progress?: number | null

src/Utils/event-buffer.ts

@@ -1,5 +1,4 @@
 import EventEmitter from 'events'
-import { proto } from '../../WAProto/index.js'
 import type {
 	BaileysEvent,
 	BaileysEventEmitter,
@@ -891,7 +890,6 @@ const makeBufferData = (): BufferedEventData => {
 			chats: {},
 			messages: {},
 			contacts: {},
-			pastParticipants: {},
 			isLatest: false,
 			empty: true
 		},
@@ -969,28 +967,10 @@ function append<E extends BufferableEvent>(
 				}
 			}
 
-			// Merge pastParticipants with deduplication by groupJid and by userJid within each group.
-			// Multiple HistorySync chunks can carry the same group -- we merge rather than concatenate
-			// to avoid duplicate entries in the final event delivered to the consumer.
-			for (const group of (eventData.pastParticipants ?? []) as proto.IPastParticipants[]) {
-				const groupJid = group.groupJid
-				if (!groupJid) continue
-
-				if (!data.historySets.pastParticipants[groupJid]) {
-					data.historySets.pastParticipants[groupJid] = []
-				}
-
-				const existing = data.historySets.pastParticipants[groupJid]
-				const seenJids = new Set(existing.map(p => p.userJid).filter(Boolean))
-
-				for (const participant of (group.pastParticipants ?? []) as proto.IPastParticipant[]) {
-					if (participant.userJid && !seenJids.has(participant.userJid)) {
-						existing.push(participant)
-						seenJids.add(participant.userJid)
-					}
-				}
-			}
-
+			data.historySets.pastParticipants = [
+				...(data.historySets.pastParticipants || []),
+				...(eventData.pastParticipants || [])
+			]
 			data.historySets.empty = false
 			data.historySets.syncType = eventData.syncType
 			data.historySets.progress = eventData.progress
@@ -1316,10 +1296,7 @@ function consolidateEvents(data: BufferedEventData) {
 			chats: Object.values(data.historySets.chats),
 			messages: Object.values(data.historySets.messages),
 			contacts: Object.values(data.historySets.contacts),
-			// Convert dedup map back to array. Each entry has groupJid + participants (all unique userJids).
-			pastParticipants: Object.entries(data.historySets.pastParticipants).map(
-				([groupJid, participants]) => ({ groupJid, pastParticipants: participants })
-			),
+			pastParticipants: data.historySets.pastParticipants,
 			syncType: data.historySets.syncType,
 			progress: data.historySets.progress,
 			isLatest: data.historySets.isLatest,

src/Utils/history.ts

@@ -374,25 +374,11 @@ export const processHistoryMessage = (item: proto.IHistorySync, logger?: ILogger
 	// Convert Map back to array for return
 	const lidPnMappings = Array.from(lidPnMap.values())
 
-	// Normalize pastParticipants: resolve LID userJids → PN so the consumer always
-	// receives a phone number, never an opaque LID identifier.
-	// Uses the lidPnMap built above (populated from phoneNumberToLidMappings + conversations).
-	// If a LID cannot be resolved, the original value is kept rather than dropping the participant.
-	const pastParticipants: proto.IPastParticipants[] = (item.pastParticipants ?? []).map(group => ({
-		groupJid: group.groupJid,
-		pastParticipants: (group.pastParticipants ?? []).map(participant => {
-			const userJid = participant.userJid
-			if (!userJid || !isAnyLidUser(userJid)) return participant
-			const mapping = lidPnMap.get(jidNormalizedUser(userJid))
-			return mapping?.pn ? { ...participant, userJid: mapping.pn } : participant
-		})
-	}))
-
 	return {
 		chats,
 		contacts,
 		messages,
-		pastParticipants,
+		pastParticipants: item.pastParticipants,
 		lidPnMappings,
 		syncType: item.syncType,
 		progress: item.progress