feat(sense): T-G0 语义分析器骨架（包结构/DDL/灰度门控挂载）

- gateway/sense/：config（SenseConfig：mode 灰度三态/特征门/conformal/consumers
  档位映射，mode 非法回落 collect）、errors（EmbedderDown/ArtifactMissing，D-G4 降级）、
  store（tier_observations + sense_artifacts DDL，WAL；观察写入/标签回填/
  labeled 查询/180d 清理/工件登记与 active 切换）、routes（/sense/health 透出灰度状态）
- settings DEFAULTS 增 sense 段（enabled 默认 False，mode 默认 collect——D-G7）
- api.py include_router 门控（装配失败不拖垮主应用）
- 测试 +5：门控 404/DDL 幂等/配置缺省与 mode 回落/独立挂载 health/
  观察写入-回填-计数-清理链路，全量 375 passed

tests/test_sense_routes.py

@@ -0,0 +1,79 @@
+"""语义分析器骨架测试（T-G0）：enabled 门控 / DDL / 独立挂载 / 配置构建。"""
+import pytest
+
+pytest.importorskip("fastapi")
+
+from fastapi import FastAPI
+from fastapi.testclient import TestClient
+
+import gateway.api as ga
+from gateway.sense.config import build_sense_config
+from gateway.sense.store import SenseStore
+
+
+def test_sense_disabled_by_default_404():
+    """D-G7：默认 enabled=False -> 全局 app 不注册任何 /sense 路由。"""
+    client = TestClient(ga.app)
+    assert client.get("/sense/health").status_code == 404
+    assert client.get("/sense/admin/agreement").status_code == 404
+
+
+def test_ddl_creates_tables_and_indexes(tmp_path):
+    """两表 + 两索引幂等创建。"""
+    store = SenseStore.init_db(tmp_path / "sense.sqlite3")
+    tables = set(store.table_names())
+    assert {"tier_observations", "sense_artifacts"} <= tables
+    idx = set(store.index_names())
+    assert {"idx_obs_ts", "idx_obs_policy"} <= idx
+    SenseStore.init_db(tmp_path / "sense.sqlite3")     # 幂等
+
+
+def test_build_sense_config_defaults():
+    """缺省值 + mode 非法回落 collect（D-G7）。"""
+    cfg = build_sense_config({})
+    assert cfg.enabled is False
+    assert cfg.mode == "collect"
+    assert cfg.embedder.dim == 1024
+    assert cfg.min_labels == 500
+    assert cfg.tier_pool_hint("proxy", "t1") == "local-small"
+    assert cfg.tier_pool_hint("proxy", "t3") == "premium"
+    assert cfg.tier_pool_hint("client", "t2") == "budget"   # 无配置兜底
+    bad = build_sense_config({"sense": {"mode": "turbo", "enabled": True}})
+    assert bad.mode == "collect"
+
+
+def test_enabled_router_health(tmp_path):
+    """enabled=True 独立挂载：/sense/health 透出灰度状态。"""
+    cfg = build_sense_config({"sense": {"enabled": True, "mode": "collect",
+                                        "db_path": str(tmp_path / "s.sqlite3")}})
+    app = FastAPI()
+    app.include_router(
+        __import__("gateway.sense", fromlist=["x"]).build_sense_router(cfg))
+    client = TestClient(app)
+    r = client.get("/sense/health")
+    assert r.status_code == 200
+    data = r.json()
+    assert data["enabled"] is True and data["mode"] == "collect"
+
+
+def test_observation_roundtrip(tmp_path):
+    """观察写入/标签回填/计数/留存清理（store 基础链路）。"""
+    store = SenseStore.init_db(tmp_path / "s.sqlite3")
+    store.insert_observation({
+        "request_id": "r1", "consumer": "pipeline", "decided_tier": "T2",
+        "executed_tier": "T2", "probs": '{"t1":0.2,"t2":0.6,"t3":0.2}',
+        "policy_version": "v0-rule", "features": '{"turns":1}'})
+    store.insert_observation({
+        "request_id": "r2", "consumer": "proxy", "decided_tier": "T1",
+        "executed_tier": "T1", "probs": "{}", "policy_version": "v0-rule",
+        "features": "{}", "outcome": "ok"})
+    assert store.count_labeled() == 0
+    store.set_true_tier("r1", "T2")
+    assert store.count_labeled() == 1
+    rows = store.labeled_rows()
+    assert rows[0]["request_id"] == "r1" and rows[0]["true_tier"] == "T2"
+    assert store.update_outcome("r2", "escalated", executed_tier="T2") is True
+    # 180d 清理
+    import time
+    assert store.purge_older_than(time.time() + 10) >= 2
+    assert store.count_labeled() == 0