feat(matrix-web): add read receipt indicators

- Add ReadReceipt type for tracking who read messages
- Track read receipts via Matrix SDK receipt events
- Display single checkmark for sent messages
- Display blue double checkmarks when message is read
- Tooltip shows names of readers
- Auto-refresh timeline when receipts are received

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

apps/matrix/apps/web/src/lib/components/chat/Message.svelte

@@ -16,6 +16,8 @@
 		Lock,
 		Warning,
 		Smiley,
+		Check,
+		Checks,
 	} from '@manacore/shared-icons';
 
 	interface Props {
@@ -486,11 +488,27 @@
 			</div>
 		{/if}
 
-		<!-- Time (shown on hover) -->
+		<!-- Time and read status -->
 		<div
-			class="flex items-center gap-2 mt-1.5 px-1 opacity-0 group-hover:opacity-100 transition-opacity"
+			class="flex items-center gap-1.5 mt-1.5 px-1 {message.isOwn ? 'justify-end' : ''}"
 		>
-			<span class="text-xs text-muted-foreground">{formattedTime()}</span>
+			<span class="text-xs text-muted-foreground opacity-0 group-hover:opacity-100 transition-opacity">{formattedTime()}</span>
+			<!-- Read receipt indicator (for own messages) -->
+			{#if message.isOwn}
+				{#if message.readBy && message.readBy.length > 0}
+					<Checks
+						class="h-4 w-4 text-blue-500"
+						weight="bold"
+						title="Gelesen von: {message.readBy.map(r => r.userName).join(', ')}"
+					/>
+				{:else}
+					<Check
+						class="h-4 w-4 text-muted-foreground/50"
+						weight="bold"
+						title="Gesendet"
+					/>
+				{/if}
+			{/if}
 		</div>
 
 		<!-- Message actions (hover) -->

apps/matrix/apps/web/src/lib/matrix/store.svelte.ts

@@ -7,6 +7,7 @@ import type {
 	SimpleMessage,
 	MessageType,
 	MessageReaction,
+	ReadReceipt,
 	RoomMember,
 	VerificationStatus,
 	DeviceInfo,
@@ -300,6 +301,14 @@ class MatrixStore {
 			// Also trigger room list update for DMs
 			this._rooms = this._client!.getRooms();
 		});
+
+		// Read receipt updates
+		this._client.on(sdk.RoomEvent.Receipt, (event, room) => {
+			// Update timeline if we're in this room to refresh read receipts
+			if (room.roomId === this._currentRoomId) {
+				this._timeline = [...(room.getLiveTimeline().getEvents() || [])];
+			}
+		});
 	}
 
 	/**
@@ -1328,6 +1337,10 @@ class MatrixStore {
 		// Collect reactions for this message
 		const reactions = this.getReactionsForEvent(event.getId() || '', timeline);
 
+		// Get read receipts for this message (only for own messages)
+		const isOwn = event.getSender() === this._client?.getUserId();
+		const readBy = isOwn ? this.getReadReceiptsForEvent(event) : undefined;
+
 		return {
 			id: event.getId() || '',
 			sender: event.getSender() || '',
@@ -1336,13 +1349,14 @@ class MatrixStore {
 			formattedBody: content.formatted_body,
 			timestamp: event.getTs(),
 			type: msgtype as MessageType,
-			isOwn: event.getSender() === this._client?.getUserId(),
+			isOwn,
 			replyTo: replyToId,
 			replyToBody,
 			edited: !!event.replacingEvent(),
 			redacted: isRedacted,
 			media,
 			reactions: reactions.length > 0 ? reactions : undefined,
+			readBy: readBy && readBy.length > 0 ? readBy : undefined,
 		};
 	}
 
@@ -1398,6 +1412,44 @@ class MatrixStore {
 		return reactions.sort((a, b) => b.count - a.count);
 	}
 
+	/**
+	 * Get read receipts for a specific event
+	 */
+	private getReadReceiptsForEvent(event: MatrixEvent): ReadReceipt[] {
+		const eventId = event.getId();
+		const roomId = event.getRoomId();
+		if (!eventId || !roomId || !this._client) return [];
+
+		const room = this._client.getRoom(roomId);
+		if (!room) return [];
+
+		const myUserId = this._client.getUserId();
+		const receipts: ReadReceipt[] = [];
+
+		// Get all members who have read up to or past this event
+		const members = room.getJoinedMembers();
+		for (const member of members) {
+			// Skip self
+			if (member.userId === myUserId) continue;
+
+			// Get the user's read receipt
+			const receiptEvent = room.getEventReadUpTo(member.userId);
+			if (!receiptEvent) continue;
+
+			// Check if their read receipt is at or after this event
+			const receiptEventObj = room.findEventById(receiptEvent);
+			if (receiptEventObj && receiptEventObj.getTs() >= event.getTs()) {
+				receipts.push({
+					userId: member.userId,
+					userName: member.name || member.userId.split(':')[0].substring(1),
+					timestamp: receiptEventObj.getTs(),
+				});
+			}
+		}
+
+		return receipts;
+	}
+
 	/**
 	 * Get display name for message sender
 	 */

apps/matrix/apps/web/src/lib/matrix/types.ts

@@ -39,6 +39,15 @@ export interface MessageReaction {
 	includesMe: boolean;
 }
 
+/**
+ * Read receipt info for a message
+ */
+export interface ReadReceipt {
+	userId: string;
+	userName: string;
+	timestamp: number;
+}
+
 /**
  * Simplified message for UI rendering
  */
@@ -57,6 +66,8 @@ export interface SimpleMessage {
 	redacted?: boolean;
 	media?: MediaInfo;
 	reactions?: MessageReaction[];
+	// Read receipts
+	readBy?: ReadReceipt[];
 }
 
 export type MessageType =