diff --git a/src/services/chatAnalyticsService.ts b/src/services/chatAnalyticsService.ts
new file mode 100644
index 0000000..957ef4d
--- /dev/null
+++ b/src/services/chatAnalyticsService.ts
@@ -0,0 +1,110 @@
+import { logger } from "firebase-functions";
+import type { CrisisType } from "./chatFilterService";
+import type { KnowledgeLevel, TeamCode } from "../types/panit";
+
+/**
+ * 채팅 관측성(#3) — BigQuery 집계용 이벤트 emit.
+ *
+ * 전송 경로: 구조화 로그(여기) → Cloud Logging 싱크 → BigQuery 데이터셋. 함수 요청 경로에
+ * 네트워크 호출을 더하지 않도록 "로그만" 남기고(지연 0·새 의존성 0), BQ 적재는 로그 싱크가
+ * 비동기로 처리한다. 싱크 설정·집계 쿼리는 docs/chat-analytics-bigquery.md 참고.
+ *
+ * 프라이버시: 메시지·응답 "본문"은 어떤 필드에도 담지 않는다 — 길이(msgLen)·메타만 남긴다.
+ */
+
+/** 싱크 필터가 채팅 이벤트 행을 고르는 마커(jsonPayload.event). 바꾸면 싱크 필터도 갱신. */
+export const CHAT_EVENT_MARKER = "chat_exchange";
+/** 스키마 버전 — 필드 추가/의미 변경 시 올린다(BQ 쪽 호환 추적용). */
+export const CHAT_EVENT_SCHEMA_VERSION = 1;
+
+export type ChatOutcome =
+  | "ok" // 모델 응답 정상
+  | "filtered" // 출력 필터 교체
+  | "crisis_input" // 입력 위기 감지 → 고정 응답(모델 미호출)
+  | "crisis_output" // 출력 위기 마커/문구 → 고정 응답
+  | "input_blocked" // 입력 필터/모더레이션 차단(422)
+  | "error" // provider 등 처리 실패
+  | "replay" // 멱등 재반환
+  | "rejected"; // 전역 한도 등 사전 거부
+
+export interface ChatEventInput {
+  outcome: ChatOutcome;
+  uid: string;
+  teamCode?: TeamCode | null;
+  threadId?: string | null;
+  stylePack?: string;
+  knowledgeLevel?: KnowledgeLevel | null;
+  promptVersion?: string;
+  provider?: string;
+  model?: string;
+  finishReason?: string;
+  crisis?: boolean;
+  crisisType?: CrisisType;
+  filtered?: boolean;
+  /** checkOutput 사유(canary/prompt-leak/hate/...) — 본문 아님. */
+  filterReason?: string;
+  /** 입력 차단 카테고리(hate/sexual/minor/insult) 또는 "moderation". */
+  blockedCategory?: string;
+  /** 모델이 실제 호출한 도구 이름들(표시용 첨부 여부와 무관). */
+  toolNames?: string[];
+  tokensIn?: number;
+  tokensOut?: number;
+  tokensCached?: number;
+  latencyMs?: number;
+  /** 사용자 메시지 "길이"만(본문 X). */
+  msgLen?: number;
+  /** HttpError code/에러 name(본문 X). */
+  errorCode?: string;
+}
+
+/**
+ * 평탄한 이벤트 객체 생성(순수 함수, 테스트 대상). undefined/null 필드는 빼서 BQ 스키마를
+ * 깔끔히 유지하고, 메시지·응답 본문은 절대 포함하지 않는다.
+ */
+export function buildChatEvent(input: ChatEventInput): Record<string, unknown> {
+  const ev: Record<string, unknown> = {
+    event: CHAT_EVENT_MARKER,
+    schema: CHAT_EVENT_SCHEMA_VERSION,
+    outcome: input.outcome,
+    uid: input.uid,
+  };
+  const put = (k: string, v: unknown): void => {
+    if (v !== undefined && v !== null) ev[k] = v;
+  };
+  put("teamCode", input.teamCode);
+  put("threadId", input.threadId);
+  put("stylePack", input.stylePack);
+  put("knowledgeLevel", input.knowledgeLevel);
+  put("promptVersion", input.promptVersion);
+  put("provider", input.provider);
+  put("model", input.model);
+  put("finishReason", input.finishReason);
+  put("crisis", input.crisis);
+  put("crisisType", input.crisisType);
+  put("filtered", input.filtered);
+  put("filterReason", input.filterReason);
+  put("blockedCategory", input.blockedCategory);
+  if (input.toolNames) {
+    ev.toolNames = input.toolNames;
+    ev.toolCount = input.toolNames.length;
+  }
+  put("tokensIn", input.tokensIn);
+  put("tokensOut", input.tokensOut);
+  put("tokensCached", input.tokensCached);
+  if (typeof input.tokensIn === "number" && typeof input.tokensOut === "number") {
+    ev.tokensTotal = input.tokensIn + input.tokensOut;
+  }
+  put("latencyMs", input.latencyMs);
+  put("msgLen", input.msgLen);
+  put("errorCode", input.errorCode);
+  return ev;
+}
+
+/** 이벤트를 구조화 로그로 emit. best-effort — 절대 throw하지 않는다(응답 경로 보호). */
+export function logChatEvent(input: ChatEventInput): void {
+  try {
+    logger.write({ severity: "INFO", message: CHAT_EVENT_MARKER, ...buildChatEvent(input) });
+  } catch {
+    // 분석 로깅 실패가 사용자 응답을 막지 않는다.
+  }
+}
diff --git a/src/services/chatService.ts b/src/services/chatService.ts
index c57cd9e..8d8912b 100644
--- a/src/services/chatService.ts
+++ b/src/services/chatService.ts
@@ -28,6 +28,7 @@ import {
   type ChatProviderMessage,
 } from "./chatProviderService";
 import { checkInput, checkOutput, crisisReply, detectCrisis } from "./chatFilterService";
+import { logChatEvent } from "./chatAnalyticsService";
 import { assemblePrompt, gatherUserContext, resolveTeamCode, type UserContext } from "./chatContextService";
 import { buildChatTools } from "./chatToolService";
 import { FALLBACK_SUGGESTION_IDS, FILTERED_REPLY, INPUT_BLOCKED_NOTICE } from "../constants/chatPrompts";
@@ -163,6 +164,7 @@ const usageWarnedDates = new Set<string>();
 
 /** `POST /chat/messages`(§3.1). */
 export async function sendMessage(uid: string, body: SendBody): Promise<ChatSendResult> {
+  const startedAt = Date.now(); // 관측성(#3) 지연 측정 기준
   // 2) 입력 검증
   const config = await getChatConfig();
   const { message, clientMessageId } = validateSendBody(body, config);
@@ -174,6 +176,10 @@ export async function sendMessage(uid: string, body: SendBody): Promise<ChatSend
   }
   const globalUsage = await getGlobalUsage(date);
   if (globalUsage >= config.globalDailyCallLimit) {
+    logChatEvent({
+      outcome: "rejected", uid, errorCode: "GLOBAL_LIMIT",
+      msgLen: message.length, latencyMs: Date.now() - startedAt,
+    });
     throw new HttpError(503, "daily global call limit reached", "AI_UNAVAILABLE");
   }
   if (globalUsage >= config.globalDailyCallLimit * 0.8 && !usageWarnedDates.has(date)) {
@@ -195,6 +201,10 @@ export async function sendMessage(uid: string, body: SendBody): Promise<ChatSend
     const inputCheck = checkInput(message, config.filters);
     if (inputCheck.blocked) {
       await recordBlockedAttemptTx(uid, date, config.dailyLimit, config.blockThresholdPerDay);
+      logChatEvent({
+        outcome: "input_blocked", uid, blockedCategory: inputCheck.category,
+        msgLen: message.length, latencyMs: Date.now() - startedAt,
+      });
       throw new HttpError(422, `input blocked (${inputCheck.category})`, "INPUT_BLOCKED", {
         notice: INPUT_BLOCKED_NOTICE,
       });
@@ -226,6 +236,10 @@ export async function sendMessage(uid: string, body: SendBody): Promise<ChatSend
 
   // 멱등 재반환 — 항상 pin된 threadId 기준(처리 도중 응원팀 변경에도 원래 스레드)
   if (outcome.kind === "done") {
+    logChatEvent({
+      outcome: "replay", uid, threadId: outcome.threadId,
+      msgLen: message.length, latencyMs: Date.now() - startedAt,
+    });
     return replayDone(uid, date, config, outcome.threadId, outcome.assistantMessageId);
   }
 
@@ -256,6 +270,12 @@ export async function sendMessage(uid: string, body: SendBody): Promise<ChatSend
       await refundWithRetry(uid, clientMessageId);
       throw err;
     }
+    logChatEvent({
+      outcome: "crisis_input", uid, teamCode: activeTeamCode, threadId: activeThreadId,
+      stylePack: config.stylePack, promptVersion: config.promptVersion,
+      crisis: true, crisisType: crisis.type,
+      msgLen: message.length, latencyMs: Date.now() - startedAt,
+    });
     return buildSendResult(uid, date, config, saved.assistantMessageId, reply, true, saved.createdAt);
   }
 
@@ -278,6 +298,10 @@ export async function sendMessage(uid: string, body: SendBody): Promise<ChatSend
       if (moderation.blocked) {
         await refundWithRetry(uid, clientMessageId);
         await recordBlockedAttemptTx(uid, date, config.dailyLimit, config.blockThresholdPerDay);
+        logChatEvent({
+          outcome: "input_blocked", uid, teamCode: activeTeamCode, threadId: activeThreadId,
+          blockedCategory: "moderation", msgLen: message.length, latencyMs: Date.now() - startedAt,
+        });
         throw new HttpError(422, "input blocked (moderation)", "INPUT_BLOCKED", {
           notice: INPUT_BLOCKED_NOTICE,
         });
@@ -296,6 +320,11 @@ export async function sendMessage(uid: string, body: SendBody): Promise<ChatSend
     } catch (err) {
       if (err instanceof HttpError) throw err;
       console.error("[chat] provider 호출 실패", err);
+      logChatEvent({
+        outcome: "error", uid, teamCode: activeTeamCode, threadId: activeThreadId,
+        stylePack: config.stylePack, provider: config.provider.name, model: config.provider.model,
+        errorCode: "AI_UNAVAILABLE", msgLen: message.length, latencyMs: Date.now() - startedAt,
+      });
       throw new HttpError(503, "AI provider unavailable", "AI_UNAVAILABLE");
     }
     // 일일 토큰 사용량 합산(§8.3) — best-effort, 실패가 응답을 막지 않는다
@@ -340,6 +369,20 @@ export async function sendMessage(uid: string, body: SendBody): Promise<ChatSend
     finalReply = reply;
     finalCrisis = crisisOut;
     finalToolCalls = toolCalls;
+    logChatEvent({
+      outcome: crisisOut ? "crisis_output" : filtered ? "filtered" : "ok",
+      uid, teamCode: activeTeamCode, threadId: activeThreadId,
+      stylePack: config.stylePack, knowledgeLevel: ctx.knowledgeLevel, promptVersion: config.promptVersion,
+      provider: config.provider.name, model: config.provider.model,
+      finishReason: result.finishReason,
+      crisis: crisisOut, crisisType: crisisOut ? (outputCheck.crisisType ?? "selfHarm") : undefined,
+      filtered, filterReason: outputCheck.action === "filter" ? outputCheck.reason : undefined,
+      toolNames: result.toolCalls.map((t) => t.name),
+      tokensIn: result.usage.inputTokens,
+      tokensOut: result.usage.outputTokens,
+      tokensCached: result.usage.cachedTokens,
+      latencyMs: Date.now() - startedAt, msgLen: message.length,
+    });
   } catch (err) {
     // 저장(처리 10) 이전 실패 — 차감분 복원(§3.1 복원 규칙). 422 모더레이션 경로는 이미
     // 복원됐고, 저장 완료(done) 후에는 refundTx가 복원을 거부한다(§6.2 차감 유지).
diff --git a/tests/services/chatAnalyticsService.test.ts b/tests/services/chatAnalyticsService.test.ts
new file mode 100644
index 0000000..53489c5
--- /dev/null
+++ b/tests/services/chatAnalyticsService.test.ts
@@ -0,0 +1,91 @@
+import { describe, it, expect } from "vitest";
+import {
+  buildChatEvent,
+  logChatEvent,
+  CHAT_EVENT_MARKER,
+  CHAT_EVENT_SCHEMA_VERSION,
+} from "../../src/services/chatAnalyticsService";
+import { KnowledgeLevel, TeamCode } from "../../src/types/panit";
+
+describe("chatAnalyticsService.buildChatEvent", () => {
+  it("필수 메타(마커·스키마·outcome·uid)를 항상 포함한다", () => {
+    const ev = buildChatEvent({ outcome: "ok", uid: "u1" });
+    expect(ev.event).toBe(CHAT_EVENT_MARKER);
+    expect(ev.schema).toBe(CHAT_EVENT_SCHEMA_VERSION);
+    expect(ev.outcome).toBe("ok");
+    expect(ev.uid).toBe("u1");
+  });
+
+  it("메시지·응답 본문은 어떤 필드에도 담지 않는다(길이만)", () => {
+    const ev = buildChatEvent({
+      outcome: "ok",
+      uid: "u1",
+      msgLen: 42,
+    });
+    expect(ev.msgLen).toBe(42);
+    // 본문류 키가 절대 없어야 한다.
+    for (const k of ["message", "reply", "content", "text", "userContent", "assistantContent", "q"]) {
+      expect(ev[k]).toBeUndefined();
+    }
+  });
+
+  it("undefined/null 필드는 제거해 BQ 스키마를 깔끔히 유지한다", () => {
+    const ev = buildChatEvent({
+      outcome: "crisis_input",
+      uid: "u1",
+      teamCode: null,
+      model: undefined,
+      knowledgeLevel: null,
+    });
+    expect("teamCode" in ev).toBe(false);
+    expect("model" in ev).toBe(false);
+    expect("knowledgeLevel" in ev).toBe(false);
+  });
+
+  it("toolNames에서 toolCount, 토큰에서 tokensTotal을 파생한다", () => {
+    const ev = buildChatEvent({
+      outcome: "ok",
+      uid: "u1",
+      toolNames: ["get_lineup", "get_team_rank_snapshot"],
+      tokensIn: 1000,
+      tokensOut: 120,
+      tokensCached: 800,
+    });
+    expect(ev.toolNames).toEqual(["get_lineup", "get_team_rank_snapshot"]);
+    expect(ev.toolCount).toBe(2);
+    expect(ev.tokensTotal).toBe(1120);
+    expect(ev.tokensCached).toBe(800);
+  });
+
+  it("빈 toolNames도 toolCount 0으로 명시한다", () => {
+    const ev = buildChatEvent({ outcome: "ok", uid: "u1", toolNames: [] });
+    expect(ev.toolCount).toBe(0);
+  });
+
+  it("성공 케이스의 차원 필드를 그대로 싣는다", () => {
+    const ev = buildChatEvent({
+      outcome: "ok",
+      uid: "u1",
+      teamCode: TeamCode.OB,
+      threadId: "OB",
+      stylePack: "commentator",
+      knowledgeLevel: KnowledgeLevel.Casual,
+      promptVersion: "2026-06-12.1",
+      provider: "vertex",
+      model: "gemini-3.1-flash-lite",
+      finishReason: "stop",
+      latencyMs: 3400,
+    });
+    expect(ev.teamCode).toBe(TeamCode.OB);
+    expect(ev.stylePack).toBe("commentator");
+    expect(ev.knowledgeLevel).toBe(KnowledgeLevel.Casual);
+    expect(ev.finishReason).toBe("stop");
+    expect(ev.latencyMs).toBe(3400);
+  });
+});
+
+describe("chatAnalyticsService.logChatEvent", () => {
+  it("best-effort — 어떤 입력에도 throw하지 않는다", () => {
+    expect(() => logChatEvent({ outcome: "error", uid: "u1", errorCode: "AI_UNAVAILABLE" })).not.toThrow();
+  });
+});