diff --git a/app/api/v1/compare_record.py b/app/api/v1/compare_record.py
index 174a087..af1f88d 100644
--- a/app/api/v1/compare_record.py
+++ b/app/api/v1/compare_record.py
@@ -12,6 +12,7 @@
 from __future__ import annotations
 
 import logging
+import uuid
 
 from fastapi import APIRouter, BackgroundTasks, HTTPException, Query, status
 
@@ -53,6 +54,10 @@ def reserve_compare_start(
         scope=risk_repo.SCOPE_ECONOMIC_ACCOUNT,
     ):
         raise HTTPException(status_code=403, detail="账号存在异常，该功能暂不可用")
+    # trace_id 统一由服务端签发（客户端不带时）：预占额度本就是任务的第一个请求，
+    # 签发与建 running 行合一，此后 Phase1/Phase2/记录/前端日志全链用同一个 id。
+    # 客户端带了则沿用——老客户端兼容 + 同 trace 重试幂等（reserve_daily_start 按 trace_id 去重）。
+    trace_id = payload.trace_id or str(uuid.uuid4())
     try:
         policy = limit_policy.resolve(
             db,
@@ -63,7 +68,7 @@ def reserve_compare_start(
         rec, used = crud_compare.reserve_daily_start(
             db,
             user_id=user.id,
-            trace_id=payload.trace_id,
+            trace_id=trace_id,
             business_type=payload.business_type,
             device_id=payload.device_id,
             limit=policy.limit,
@@ -94,6 +99,7 @@ def reserve_compare_start(
         limit=policy.limit,
         used=used,
         remaining=max(policy.limit - used, 0) if policy.limit is not None else None,
+        trace_id=trace_id,
     )
 
 
diff --git a/app/api/v1/coupon.py b/app/api/v1/coupon.py
index ecd40a8..a3179d8 100644
--- a/app/api/v1/coupon.py
+++ b/app/api/v1/coupon.py
@@ -12,6 +12,7 @@ from __future__ import annotations
 
 import json
 import logging
+import uuid
 from typing import Any
 
 import httpx
@@ -30,6 +31,7 @@ from app.schemas.coupon_state import (
     CouponPromptShouldShowOut,
     CouponPromptShownIn,
     CouponSessionIn,
+    CouponSessionOut,
     CouponStatsOut,
 )
 
@@ -175,6 +177,12 @@ async def coupon_step(
         )
 
     resp_json = resp.json()
+    # 每帧响应顶层回传本次任务 trace_id(对齐 compare _forward 的 setdefault):客户端任一帧
+    # 都能从响应拿到全链 id。**只回显请求里带的、不 mint**——step 是循环接口,每帧签新 id
+    # 会把一次任务打散;领券 trace_id 的唯一签发点在 /coupon/session (status=started)。
+    # pricebot 响应顶层本无 trace_id(只有 trace_url),setdefault 不会覆盖任何上游值。
+    if isinstance(resp_json, dict) and trace_id:
+        resp_json.setdefault("trace_id", trace_id)
 
     # 领券结果沉淀:每日资产 + 逐次事件；中间帧和 done 全量帧均幂等写库。
     # 当前只记录、不参与"要不要领"判断(MVP 先不去重)。写库失败不影响返回。
@@ -204,15 +212,33 @@ async def coupon_step(
     return resp_json
 
 
-@router.post("/session", summary="领券任务流水上报(admin 领券数据看板数据源)")
-def coupon_session(payload: CouponSessionIn, db: DbSession) -> dict[str, bool]:
+@router.post(
+    "/session",
+    response_model=CouponSessionOut,
+    summary="领券任务流水上报(admin 领券数据看板数据源;started 兼签发本轮 trace_id)",
+)
+def coupon_session(payload: CouponSessionIn, db: DbSession) -> CouponSessionOut:
     """客户端两段上报一次领券流水(发起 started / 收尾 completed-failed-abandoned),按 trace_id upsert
     到 coupon_session。不鉴权(同领券循环 MVP,按 device_id/trace_id);供 admin「领券数据」看板算
-    发起/完成数、耗时分位、机型维度。写库失败不应连累客户端(本就 fire-and-forget),吞掉返回 ok。"""
+    发起/完成数、耗时分位、机型维度。写库失败不应连累客户端(本就 fire-and-forget),吞掉返回 ok。
+
+    trace_id 统一由后端签发:started 不带 trace_id → 签发 uuid 并随响应返回,客户端全程用它
+    (领券 step 循环 / 收尾上报 / 前端运行日志)。签发不依赖写库成功——写库失败照样返回 trace_id,
+    后续收尾上报 upsert 会补建行。非 started 缺 trace_id 不签发(收尾没有 id 只能是异常调用,
+    签发新 id 只会造出一行查不到发起信息的孤儿),不写库、trace_id=null 返回。
+    """
+    trace_id = payload.trace_id or (
+        str(uuid.uuid4()) if payload.status == "started" else None
+    )
+    if trace_id is None:
+        logger.warning(
+            "coupon session missing trace_id for status=%s (skip write)", payload.status
+        )
+        return CouponSessionOut(ok=True, trace_id=None)
     try:
         coupon_repo.upsert_coupon_session(
             db,
-            trace_id=payload.trace_id,
+            trace_id=trace_id,
             device_id=payload.device_id,
             status=payload.status,
             started_at_ms=payload.started_at_ms,
@@ -229,7 +255,7 @@ def coupon_session(payload: CouponSessionIn, db: DbSession) -> dict[str, bool]:
         )
     except Exception as e:  # noqa: BLE001
         logger.warning("coupon session write failed: %s", e)
-    return {"ok": True}
+    return CouponSessionOut(ok=True, trace_id=trace_id)
 
 
 @router.post("/prompt/shown", summary="领券引导窗弹出即上报(按 App 记 shown)")
diff --git a/app/schemas/compare_record.py b/app/schemas/compare_record.py
index 4a6b617..74fde79 100644
--- a/app/schemas/compare_record.py
+++ b/app/schemas/compare_record.py
@@ -214,9 +214,13 @@ class ComparisonRecordCreatedOut(BaseModel):
 
 
 class CompareStartReserveIn(BaseModel):
-    """Reserve one authenticated comparison start before the agent begins."""
+    """Reserve one authenticated comparison start before the agent begins.
 
-    trace_id: str = Field(..., min_length=1, max_length=64)
+    trace_id 可选：不带 = 请服务端签发（统一 trace_id 由后端下发，前端/SLS 日志/
+    pricebot 全链用同一个 id）；带 = 沿用客户端值（老客户端兼容 + 网络重试幂等）。
+    """
+
+    trace_id: str | None = Field(default=None, min_length=1, max_length=64)
     business_type: str = Field(default="food", min_length=1, max_length=16)
     device_id: str | None = Field(default=None, max_length=64)
 
@@ -225,6 +229,9 @@ class CompareStartReserveOut(BaseModel):
     limit: int | None
     used: int
     remaining: int | None
+    # 本次比价全链 trace_id（服务端签发的，或回显客户端带来的）。客户端必须以它为准，
+    # 贯穿 Phase1/Phase2 step、比价记录、trace 收尾与前端运行日志上报。
+    trace_id: str
 
 
 class CompareStatsOut(BaseModel):
diff --git a/app/schemas/coupon_state.py b/app/schemas/coupon_state.py
index 35d2cca..0b7ae25 100644
--- a/app/schemas/coupon_state.py
+++ b/app/schemas/coupon_state.py
@@ -58,9 +58,13 @@ class CouponSessionIn(BaseModel):
     - 发起(status=started):带勾选平台 + 机型/ROM/app_env + started_at_ms(发起墙钟毫秒)。
     - 收尾(completed/failed/abandoned):带 elapsed_ms(全程耗时)+ platform_elapsed(各平台耗时)+ claimed_count。
     不鉴权(同领券循环 MVP,按 device_id/trace_id),user_id 登录态带上做留痕(可空)。
+
+    trace_id 可选:started 不带 = 请服务端签发本轮领券 trace_id(统一 trace_id 由后端下发,
+    响应 CouponSessionOut.trace_id 返回,客户端全程用它);带 = 沿用客户端值(老客户端兼容)。
+    非 started 缺 trace_id 不签发(防孤儿行),返回 trace_id=null 且不写库。
     """
 
-    trace_id: str
+    trace_id: str | None = None
     device_id: str
     status: str  # started / completed / failed / abandoned
     started_at_ms: int  # 发起墙钟毫秒(客户端 System.currentTimeMillis)
@@ -74,3 +78,16 @@ class CouponSessionIn(BaseModel):
     platform_elapsed: dict[str, int] | None = None
     claimed_count: int | None = None
     trace_url: str | None = None
+
+
+class CouponSessionOut(BaseModel):
+    """POST /api/v1/coupon/session 响应。
+
+    trace_id = 本轮领券全链 id(服务端签发的,或回显客户端带来的);客户端以它为准贯穿
+    /coupon/step 循环、收尾上报与前端运行日志。⚠️ 不能沿用旧的 dict[str, bool] 返回注解——
+    FastAPI 会按注解校验响应,字符串 trace_id 过 bool 校验必炸,故显式建模。
+    非 started 且缺 trace_id 时为 null(不签发防孤儿行)。
+    """
+
+    ok: bool = True
+    trace_id: str | None = None
diff --git a/tests/test_compare_daily_limit.py b/tests/test_compare_daily_limit.py
index a10afec..1de1a56 100644
--- a/tests/test_compare_daily_limit.py
+++ b/tests/test_compare_daily_limit.py
@@ -48,7 +48,10 @@ def test_compare_start_is_idempotent_by_trace_id(client) -> None:
     retry = client.post("/api/v1/compare/start", json=payload, headers=_headers(token))
 
     assert first.status_code == 200, first.text
-    assert first.json() == {"limit": 100, "used": 1, "remaining": 99}
+    # trace_id 回显客户端带来的值(老协议幂等路径)
+    assert first.json() == {
+        "limit": 100, "used": 1, "remaining": 99, "trace_id": payload["trace_id"],
+    }
     assert retry.status_code == 200, retry.text
     assert retry.json() == first.json()
     with SessionLocal() as db:
@@ -69,6 +72,28 @@ def test_compare_start_is_idempotent_by_trace_id(client) -> None:
     assert record.device_id == "quota-device"
 
 
+def test_compare_start_issues_trace_id_when_absent(client) -> None:
+    """新客户端不带 trace_id → 服务端签发并随响应返回,running 行以签发 id 建。"""
+    token, user_id = _login(client)
+    response = client.post(
+        "/api/v1/compare/start",
+        json={"business_type": "food", "device_id": "quota-device-issue"},
+        headers=_headers(token),
+    )
+    assert response.status_code == 200, response.text
+    body = response.json()
+    issued = body["trace_id"]
+    assert issued  # 非空签发
+    assert body["used"] == 1
+    with SessionLocal() as db:
+        record = db.execute(
+            select(ComparisonRecord).where(ComparisonRecord.trace_id == issued)
+        ).scalar_one()
+    assert record.user_id == user_id
+    assert record.status == "running"
+    assert record.device_id == "quota-device-issue"
+
+
 def test_compare_start_rejects_101st_beijing_day_attempt(client) -> None:
     token, user_id = _login(client)
     now = datetime.now(CN_TZ).replace(tzinfo=None)
@@ -101,7 +126,9 @@ def test_compare_start_rejects_101st_beijing_day_attempt(client) -> None:
         headers=_headers(token),
     )
     assert allowed.status_code == 200, allowed.text
-    assert allowed.json() == {"limit": 100, "used": 100, "remaining": 0}
+    assert allowed.json() == {
+        "limit": 100, "used": 100, "remaining": 0, "trace_id": final_allowed_trace,
+    }
 
     rejected_trace = f"quota-rejected-{user_id}"
     response = client.post(
diff --git a/tests/test_coupon_proxy.py b/tests/test_coupon_proxy.py
index c993181..5543cd3 100644
--- a/tests/test_coupon_proxy.py
+++ b/tests/test_coupon_proxy.py
@@ -8,6 +8,7 @@ mock 掉对 pricebot 的 httpx 调用,验证:
 """
 from __future__ import annotations
 
+import json
 import time
 from unittest.mock import MagicMock, patch
 
@@ -62,7 +63,8 @@ def test_coupon_step_no_auth_required(client) -> None:
 
 
 def test_coupon_step_passes_body_through(client, access_token) -> None:
-    """带 token + pricebot 200 → 响应原样透传,请求 body 原样转发到 /api/coupon/step。"""
+    """带 token + pricebot 200 → 请求 body 原样转发到 /api/coupon/step;
+    响应在透传基础上顶层回显本次任务 trace_id(setdefault 注入,其余字段原样)。"""
     fake_pricebot_resp = {
         "success": True,
         "action": {
@@ -83,9 +85,12 @@ def test_coupon_step_passes_body_through(client, access_token) -> None:
 
     captured: dict = {}
 
-    async def fake_post(self, url, json=None, **kw):
+    # ⚠️ coupon_step 转发用 content=raw(原始字节透传,不重新 dumps),不是 json= ——
+    # fake 必须捕 content。旧 fake 只捕 json= 导致 captured["json"] 恒 None,本测试
+    # 自 content=raw 优化后一直红着(pre-existing),本次顺手修正。
+    async def fake_post(self, url, content=None, **kw):
         captured["url"] = url
-        captured["json"] = json
+        captured["content"] = content
         mock_resp = MagicMock()
         mock_resp.status_code = 200
         mock_resp.json = lambda: fake_pricebot_resp
@@ -99,9 +104,10 @@ def test_coupon_step_passes_body_through(client, access_token) -> None:
         )
 
     assert r.status_code == 200, r.text
-    assert r.json() == fake_pricebot_resp
-    # 验证请求被原样转发(body 不动 + URL 指向 pricebot)
-    assert captured["json"] == _stub_request_body()
+    # 顶层多出 trace_id 回显(值=请求带的;不 mint,签发点唯一在 /coupon/session started)
+    assert r.json() == {**fake_pricebot_resp, "trace_id": "test-trace-1"}
+    # 验证请求被原样转发(body 字节不动 + URL 指向 pricebot)
+    assert json.loads(captured["content"]) == _stub_request_body()
     assert captured["url"].endswith("/api/coupon/step")
 
 
diff --git a/tests/test_coupon_session_issue.py b/tests/test_coupon_session_issue.py
new file mode 100644
index 0000000..b9459fc
--- /dev/null
+++ b/tests/test_coupon_session_issue.py
@@ -0,0 +1,65 @@
+"""POST /api/v1/coupon/session 的 trace_id 签发行为(统一 trace_id 由后端下发)。
+
+- started 不带 trace_id → 服务端签发并返回,行以签发 id 建;
+- started 带 trace_id → 回显沿用(老客户端兼容);
+- 非 started 缺 trace_id → 不签发不写库,trace_id=null(防孤儿行)。
+"""
+from __future__ import annotations
+
+from sqlalchemy import func, select
+
+from app.db.session import SessionLocal
+from app.models.coupon_state import CouponSession
+
+
+def _base_payload(**overrides) -> dict:
+    payload = {
+        "device_id": "cs-issue-device",
+        "status": "started",
+        "started_at_ms": 1_722_000_000_000,
+        "platforms": ["meituan-waimai"],
+        "app_env": "dev",
+    }
+    payload.update(overrides)
+    return payload
+
+
+def test_session_started_issues_trace_id_when_absent(client) -> None:
+    response = client.post("/api/v1/coupon/session", json=_base_payload())
+    assert response.status_code == 200, response.text
+    body = response.json()
+    assert body["ok"] is True
+    issued = body["trace_id"]
+    assert issued
+    with SessionLocal() as db:
+        row = db.execute(
+            select(CouponSession).where(CouponSession.trace_id == issued)
+        ).scalar_one()
+    assert row.device_id == "cs-issue-device"
+    assert row.status == "started"
+
+
+def test_session_started_echoes_client_trace_id(client) -> None:
+    response = client.post(
+        "/api/v1/coupon/session", json=_base_payload(trace_id="cs-legacy-1")
+    )
+    assert response.status_code == 200, response.text
+    assert response.json()["trace_id"] == "cs-legacy-1"
+    with SessionLocal() as db:
+        count = db.scalar(
+            select(func.count(CouponSession.id)).where(
+                CouponSession.trace_id == "cs-legacy-1"
+            )
+        )
+    assert count == 1
+
+
+def test_session_terminal_without_trace_id_skips_write(client) -> None:
+    response = client.post(
+        "/api/v1/coupon/session",
+        json=_base_payload(status="completed", elapsed_ms=1234, claimed_count=2),
+    )
+    assert response.status_code == 200, response.text
+    body = response.json()
+    assert body["ok"] is True
+    assert body["trace_id"] is None