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
127
packages/dashboard/src/__tests__/chat-room-compaction.test.ts
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127
packages/dashboard/src/__tests__/chat-room-compaction.test.ts
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import { describe, expect, it } from "vitest";
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import { buildCompactedRoomTranscript } from "../chat.js";
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function makeMessage(index: number, overrides: Partial<{
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id: string;
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role: "user" | "assistant" | "system";
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content: string;
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createdAt: string;
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senderAgentId: string | null;
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}> = {}) {
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return {
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id: overrides.id ?? `msg-${index}`,
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role: overrides.role ?? (index % 2 === 0 ? "user" : "assistant"),
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content: overrides.content ?? `message-${index}`,
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createdAt: overrides.createdAt ?? `2026-01-01T00:00:${String(index).padStart(2, "0")}.000Z`,
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senderAgentId: "senderAgentId" in overrides ? (overrides.senderAgentId ?? null) : (index % 2 === 0 ? null : "agent-a"),
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};
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}
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describe("buildCompactedRoomTranscript", () => {
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it("returns all messages verbatim when the transcript fits inside the recent window", () => {
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const messages = Array.from({ length: 6 }, (_, index) => makeMessage(index));
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const transcript = buildCompactedRoomTranscript(messages, "msg-4");
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expect(transcript).not.toContain("## Earlier room context (compacted)");
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expect(transcript).toContain("message-0");
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expect(transcript).toContain("message-5");
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expect(transcript.match(/\[LATEST USER MESSAGE — ANSWER THIS\]/g)).toHaveLength(1);
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});
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it("prepends a compacted summary and keeps the last 12 messages verbatim", () => {
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const messages = Array.from({ length: 30 }, (_, index) => {
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const olderUserLengths = [40, 80, 120, 160, 200, 220, 60, 70, 90];
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const content = index < 18 && index % 2 === 0
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? `older-user-${index}-` + "u".repeat(olderUserLengths[index / 2] ?? 20)
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: `message-${index}`;
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return makeMessage(index, { content });
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});
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const latestUserMessageId = "msg-28";
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const transcript = buildCompactedRoomTranscript(messages, latestUserMessageId);
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expect(transcript).toContain("## Earlier room context (compacted)");
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expect(transcript).toContain("- Span: 18 messages from 2026-01-01T00:00:00.000Z to 2026-01-01T00:00:17.000Z");
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expect(transcript).toContain("- Participants: User, Agent agent-a");
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const [summaryBlock] = transcript.split("\n\n");
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const highlightLines = summaryBlock.split("\n").filter((line) => line.startsWith(" - "));
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expect(highlightLines).toHaveLength(5);
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const highlightTimestamps = highlightLines.map((line) => line.match(/\[(.*?)\]/)?.[1] ?? "");
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expect(highlightTimestamps).toEqual([...highlightTimestamps].sort());
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for (let index = 18; index < 30; index += 1) {
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expect(transcript).toContain(`- [2026-01-01T00:00:${String(index).padStart(2, "0")}.000Z]`);
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}
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expect(transcript).toContain("(user) User: message-28 [LATEST USER MESSAGE — ANSWER THIS]");
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});
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it("preserves the latest marker exactly once even when the transcript must shrink", () => {
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const messages = Array.from({ length: 30 }, (_, index) => makeMessage(index, {
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role: index === 29 ? "user" : (index % 3 === 0 ? "assistant" : "user"),
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senderAgentId: index % 3 === 0 ? "agent-a" : null,
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content: `message-${index}-` + "x".repeat(1500),
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}));
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const transcript = buildCompactedRoomTranscript(messages, "msg-29");
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expect(transcript.length).toBeLessThanOrEqual(8000);
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expect(transcript.match(/\[LATEST USER MESSAGE — ANSWER THIS\]/g)).toHaveLength(1);
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expect(transcript).toContain("message-29-");
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});
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it("drops summary highlights from the bottom when the summary exceeds its cap", () => {
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const olderMessages = Array.from({ length: 18 }, (_, index) => makeMessage(index, {
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role: "user",
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content: `older-${index}-` + "z".repeat(500),
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}));
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const recentMessages = Array.from({ length: 12 }, (_, index) => makeMessage(index + 18, {
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role: index === 11 ? "user" : "assistant",
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senderAgentId: index === 11 ? null : `agent-${index}`,
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content: `recent-${index}`,
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}));
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const transcript = buildCompactedRoomTranscript([...olderMessages, ...recentMessages], "msg-29");
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const [summaryBlock] = transcript.split("\n\n");
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const highlightLines = summaryBlock.split("\n").filter((line) => line.startsWith(" - "));
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expect(summaryBlock).toContain("## Earlier room context (compacted)");
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expect(summaryBlock).toContain("- Span: 18 messages");
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expect(summaryBlock).toContain("- Participants: User");
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expect(summaryBlock).toContain("- Highlights:");
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expect(summaryBlock.length).toBeLessThanOrEqual(1500);
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expect(highlightLines.length).toBeLessThan(5);
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});
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it("keeps the total transcript under the overall cap", () => {
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const messages = Array.from({ length: 80 }, (_, index) => makeMessage(index, {
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role: index === 79 ? "user" : (index % 4 === 0 ? "system" : index % 2 === 0 ? "assistant" : "user"),
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senderAgentId: index % 2 === 0 && index % 4 !== 0 ? `agent-${index}` : null,
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content: `message-${index}-` + "q".repeat(4000),
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}));
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const transcript = buildCompactedRoomTranscript(messages, "msg-79");
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expect(transcript.length).toBeLessThanOrEqual(8000);
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expect(transcript).toContain("message-79-");
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});
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it("computes unique participant labels from older messages", () => {
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const older = [
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makeMessage(0, { role: "user", senderAgentId: null, content: "user older" }),
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makeMessage(1, { role: "assistant", senderAgentId: "agent-a", content: "agent a older" }),
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makeMessage(2, { role: "system", senderAgentId: null, content: "system older" }),
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makeMessage(3, { role: "assistant", senderAgentId: null, content: "assistant older" }),
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makeMessage(4, { role: "assistant", senderAgentId: "agent-b", content: "agent b older" }),
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];
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const recent = Array.from({ length: 12 }, (_, index) => makeMessage(index + 5, {
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role: index === 11 ? "user" : "assistant",
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senderAgentId: index === 11 ? null : "agent-c",
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content: `recent-${index}`,
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}));
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const transcript = buildCompactedRoomTranscript([...older, ...recent], "msg-16");
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expect(transcript).toContain("- Participants: User, Agent agent-a, System, Assistant, Agent agent-b");
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});
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});
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@@ -205,7 +205,7 @@ describe("Chat orchestration — rooms (FN-3805..FN-3811 contract)", () => {
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expect(mockChatStore.getRoomMessages).toHaveBeenCalledWith("room-1", { limit: expect.any(Number) });
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});
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it("trims older room context entries from the prompt window", async () => {
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it("compacts older room context entries in the responder prompt", async () => {
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mockChatStore.listRoomMembers.mockReturnValue([
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{ roomId: "room-1", agentId: "agent-a", role: "member", addedAt: "2026-01-01" },
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]);
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@@ -213,6 +213,11 @@ describe("Chat orchestration — rooms (FN-3805..FN-3811 contract)", () => {
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mockAgentStore.getAgent.mockResolvedValue({ id: "agent-a", name: "Alpha", role: "executor" });
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const promptSpy = vi.fn().mockResolvedValue(undefined);
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mockChatStore.addRoomMessage.mockImplementationOnce((_roomId: string, input: any) => ({
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id: "history-latest",
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roomId: "room-1",
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...input,
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}));
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__setCreateResolvedAgentSession(async () => ({
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session: {
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prompt: promptSpy,
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@@ -232,7 +237,7 @@ describe("Chat orchestration — rooms (FN-3805..FN-3811 contract)", () => {
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}));
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history[history.length - 1] = {
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...history[history.length - 1],
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id: "msg-1",
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id: "history-latest",
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role: "user",
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senderAgentId: null,
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content: "hello @Alpha",
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@@ -246,8 +251,13 @@ describe("Chat orchestration — rooms (FN-3805..FN-3811 contract)", () => {
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await manager.sendRoomMessage("room-1", "hello @Alpha");
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const prompt = promptSpy.mock.calls[0]?.[0] as string;
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expect(prompt).toContain("## Earlier room context (compacted)");
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expect(prompt).toContain("- Span: 18 messages from 2026-01-01T00:00:00.000Z to 2026-01-01T00:00:17.000Z");
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expect(prompt).toContain("history-item-28");
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expect(prompt).not.toContain("history-item-0");
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expect(prompt).toContain(" - [2026-01-01T00:00:00.000Z] User: history-item-0");
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expect(prompt).not.toContain("- [2026-01-01T00:00:00.000Z] (user) User: history-item-0");
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expect(prompt).toContain("- [2026-01-01T00:00:29.000Z] (user) User: hello @Alpha [LATEST USER MESSAGE — ANSWER THIS]");
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expect(prompt.match(/\[LATEST USER MESSAGE — ANSWER THIS\]/g)).toHaveLength(1);
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});
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it("throws surfaced error when room has members but no resolvable responders", async () => {
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