feat(FN-4180): compact room transcript context to reduce token usage
Adds room transcript context compaction (FN-4180) to the dashboard chat layer — widens the fetch window then compacts older messages into a summary window to reduce token overhead while keeping full context recent. Includes a new 127-line test suite covering the compaction logic, a small fix to reus Fusion-Task-Id: FN-4180 Fusion-Task-Lineage: 9e7e3a32-f2da-4c86-871b-37891f747561
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Fusion
@@ -19,6 +19,7 @@ import type {
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ChatAttachment,
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ChatInFlightGenerationState,
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ChatStore,
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ChatRoomMessage,
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ChatSession,
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ChatSessionCreateInput,
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MessageStore,
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@@ -137,11 +138,126 @@ const MAX_MESSAGES_PER_IP_PER_MINUTE = 30;
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/** Maximum file size for # mentions (50KB). Files larger than this are skipped. */
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const MAX_REFERENCED_FILE_SIZE = 50 * 1024;
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const ROOM_AMBIENT_MAX_RESPONDERS = 5;
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const ROOM_THREAD_CONTEXT_MAX_MESSAGES = 16;
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const ROOM_THREAD_RECENT_VERBATIM_MESSAGES = 12;
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const ROOM_THREAD_COMPACTION_FETCH_LIMIT = 80;
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const ROOM_THREAD_CONTEXT_MAX_CHARS = 8_000;
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const ROOM_THREAD_MESSAGE_CONTENT_MAX_CHARS = 1_200;
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const ROOM_THREAD_SUMMARY_MAX_CHARS = 1_500;
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const IN_FLIGHT_PERSIST_DEBOUNCE_MS = 200;
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type RoomTranscriptMessage = Pick<ChatRoomMessage, "id" | "role" | "content" | "createdAt" | "senderAgentId">;
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function getRoomSenderLabel(message: Pick<RoomTranscriptMessage, "role" | "senderAgentId">): string {
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return message.role === "user"
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? "User"
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: message.role === "system"
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? "System"
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: (message.senderAgentId ? `Agent ${message.senderAgentId}` : "Assistant");
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}
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function truncateWithEllipsis(content: string, maxChars: number): string {
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return content.length > maxChars
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? `${content.slice(0, maxChars - 1)}…`
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: content;
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}
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function formatRoomThreadLine(message: RoomTranscriptMessage, latestUserMessageId: string): string {
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const marker = message.id === latestUserMessageId ? " [LATEST USER MESSAGE — ANSWER THIS]" : "";
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return `- [${message.createdAt}] (${message.role}) ${getRoomSenderLabel(message)}: ${truncateWithEllipsis(message.content, ROOM_THREAD_MESSAGE_CONTENT_MAX_CHARS)}${marker}`;
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}
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function formatRoomThreadContext(messages: RoomTranscriptMessage[], latestUserMessageId: string): string {
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return messages.map((message) => formatRoomThreadLine(message, latestUserMessageId)).join("\n");
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}
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function buildRoomSummaryBlock(olderMessages: RoomTranscriptMessage[]): string {
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if (olderMessages.length === 0) {
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return "";
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}
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const participants = Array.from(new Set(olderMessages.map((message) => getRoomSenderLabel(message))));
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const rankedHighlights = olderMessages
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.map((message, index) => ({
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message,
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index,
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score: (message.role === "user" ? 2 : message.role === "assistant" ? 1 : 0) * 1000 + message.content.length,
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}))
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.sort((left, right) => right.score - left.score || left.index - right.index)
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.slice(0, 5)
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.sort((left, right) => left.index - right.index)
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.map(({ message }) => ` - [${message.createdAt}] ${getRoomSenderLabel(message)}: ${truncateWithEllipsis(message.content, 240)}`);
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const summaryLines = [
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"## Earlier room context (compacted)",
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`- Span: ${olderMessages.length} messages from ${olderMessages[0]?.createdAt ?? ""} to ${olderMessages.at(-1)?.createdAt ?? ""}`,
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`- Participants: ${participants.join(", ")}`,
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"- Highlights:",
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];
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const baseSummary = summaryLines.join("\n");
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if (rankedHighlights.length === 0) {
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return baseSummary;
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}
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const highlights = [...rankedHighlights];
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while (`${baseSummary}\n${highlights.join("\n")}`.length > ROOM_THREAD_SUMMARY_MAX_CHARS && highlights.length > 0) {
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highlights.pop();
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}
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return highlights.length > 0
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? `${baseSummary}\n${highlights.join("\n")}`
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: baseSummary;
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}
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export function buildCompactedRoomTranscript(
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messages: RoomTranscriptMessage[],
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latestUserMessageId: string,
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): string {
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if (messages.length === 0) {
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return "";
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}
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const messageIndexes = new Map(messages.map((message, index) => [message.id, index]));
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const latestUserMessage = messages.find((message) => message.id === latestUserMessageId);
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const splitIndex = Math.max(0, messages.length - ROOM_THREAD_RECENT_VERBATIM_MESSAGES);
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let olderMessages = messages.slice(0, splitIndex);
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let recentMessages = messages.slice(splitIndex);
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if (latestUserMessage && !recentMessages.some((message) => message.id === latestUserMessageId)) {
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olderMessages = olderMessages.filter((message) => message.id !== latestUserMessageId);
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recentMessages = [...recentMessages, latestUserMessage]
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.sort((left, right) => (messageIndexes.get(left.id) ?? 0) - (messageIndexes.get(right.id) ?? 0));
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}
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const summaryLines = buildRoomSummaryBlock(olderMessages).split("\n").filter((line) => line.length > 0);
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const renderTranscript = () => {
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const summary = summaryLines.length > 0 ? summaryLines.join("\n") : "";
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const recent = formatRoomThreadContext(recentMessages, latestUserMessageId);
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if (summary && recent) {
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return `${summary}\n\n${recent}`;
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}
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return summary || recent;
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};
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let transcript = renderTranscript();
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while (transcript.length > ROOM_THREAD_CONTEXT_MAX_CHARS && summaryLines.at(-1)?.startsWith(" - ")) {
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summaryLines.pop();
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transcript = renderTranscript();
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}
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while (transcript.length > ROOM_THREAD_CONTEXT_MAX_CHARS && recentMessages.length > 1) {
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const removableIndex = recentMessages.findIndex((message) => message.id !== latestUserMessageId);
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if (removableIndex === -1) {
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break;
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}
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recentMessages.splice(removableIndex, 1);
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transcript = renderTranscript();
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}
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return transcript;
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}
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function formatAttachmentSize(size: number): string {
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if (size < 1024) return `${size}B`;
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if (size < 1024 * 1024) return `${(size / 1024).toFixed(1)}KB`;
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@@ -1072,12 +1188,12 @@ export class ChatManager {
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}
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systemPrompt = `${systemPrompt}\n\n${CHAT_AGENT_MESSAGE_ROUTING_GUIDANCE}`;
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const roomMessages = this.chatStore.getRoomMessages(input.roomId, { limit: ROOM_THREAD_CONTEXT_MAX_MESSAGES });
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const roomMessages = this.chatStore.getRoomMessages(input.roomId, { limit: ROOM_THREAD_COMPACTION_FETCH_LIMIT });
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const roomPrompt = [
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`You are replying as ${input.responder.name} in room #${input.roomName}.`,
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"Reply to the latest user room message in the context of this shared room thread.",
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"Room transcript (oldest to newest, bounded):",
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this.formatRoomThreadContext(roomMessages, input.latestUserMessageId),
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this.compactRoomThreadContext(roomMessages, input.latestUserMessageId),
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"Latest user message to answer:",
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input.content,
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].join("\n\n");
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@@ -1147,35 +1263,15 @@ export class ChatManager {
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}
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}
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private formatRoomThreadContext(
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messages: Array<{ id: string; role: "user" | "assistant" | "system"; content: string; createdAt: string; senderAgentId?: string | null }>,
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/**
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* Preserve the newest room turns verbatim while compacting older history into
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* a deterministic summary block so long-running rooms keep continuity.
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*/
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private compactRoomThreadContext(
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messages: RoomTranscriptMessage[],
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latestUserMessageId: string,
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): string {
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const trimmedFromTail: string[] = [];
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let totalChars = 0;
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for (let index = messages.length - 1; index >= 0; index -= 1) {
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const message = messages[index];
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const senderLabel = message.role === "user"
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? "User"
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: message.role === "system"
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? "System"
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: (message.senderAgentId ? `Agent ${message.senderAgentId}` : "Assistant");
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const content = message.content.length > ROOM_THREAD_MESSAGE_CONTENT_MAX_CHARS
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? `${message.content.slice(0, ROOM_THREAD_MESSAGE_CONTENT_MAX_CHARS - 1)}…`
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: message.content;
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const marker = message.id === latestUserMessageId ? " [LATEST USER MESSAGE — ANSWER THIS]" : "";
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const line = `- [${message.createdAt}] (${message.role}) ${senderLabel}: ${content}${marker}`;
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if (trimmedFromTail.length > 0 && totalChars + line.length > ROOM_THREAD_CONTEXT_MAX_CHARS) {
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break;
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}
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trimmedFromTail.push(line);
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totalChars += line.length;
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}
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return trimmedFromTail.reverse().join("\n");
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return buildCompactedRoomTranscript(messages, latestUserMessageId);
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}
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/**
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