fix: 孤代理三入口堵漏+精确断言+截断清洗换序

- _utf8_ok 助手：event_id/path/title 含孤代理（"\ud800"）在入口即拒
  （原会流到下游 encode 必 500）；props 字节守门 try/except 归入 properties_invalid
- 补零覆盖原因码测试：path=123 → invalid_field_type；utm 三层嵌套 → properties_depth
- 子串断言（"sensitive" in r 等）全改精确等值断言，码即 API
- path 改为先 sanitize_url 再截 500：中文查询参数 urlencode 膨胀最多 3 倍，
  先截后洗会破坏出门 ≤MAX_PATH_LEN 不变量（实测汉*200 查询洗后截回 500）
- docstring 写明就地写回契约（Task 6 ingest 依赖）

Co-Authored-By: Claude Code <noreply@anthropic.com>

server/tracker/services/validation.py

@@ -8,6 +8,14 @@ from tracker import constants as C
 _SENSITIVE = re.compile("|".join(C.SENSITIVE_KEY_PATTERNS), re.I)
 _URL_DROP_KEY = re.compile("|".join(C.URL_PARAM_DROP_PATTERNS), re.I)
 
+def _utf8_ok(s: str) -> bool:
+    """孤代理（如 "\ud800"）在下游 encode/JSON 序列化时必然 500，入口处即拒。"""
+    try:
+        s.encode("utf-8")
+        return True
+    except UnicodeEncodeError:
+        return False
+
 def sanitize_url(url: str) -> str:
     """按参数名整键删除（fullmatch 防止误伤 monkey 这类含 key 子串的参数）。"""
     p = urlparse(url)
@@ -44,16 +52,19 @@ def _walk_props(v, depth=0):
     return True, False, False
 
 def validate_event(ev) -> str | None:
-    """返回 None 表示通过；否则返回拒绝原因码。类型/白名单/体积/深度全在此守门。"""
+    """返回 None 表示通过；否则返回拒绝原因码。类型/白名单/体积/深度全在此守门。
+    通过时会就地截断/清洗并写回 ev（path 先 sanitize_url 再截 MAX_PATH_LEN，title 截
+    MAX_TITLE_LEN）——Task 6 的 ingest 依赖此写回契约。"""
     if not isinstance(ev, dict):
         return "event_invalid_shape"
     if ev.get("event_name") not in C.EVENT_NAMES:
         return "event_name_not_allowed"
     eid = ev.get("event_id")
-    if not isinstance(eid, str) or not eid or len(eid) > 64:
+    if not isinstance(eid, str) or not eid or len(eid) > 64 or not _utf8_ok(eid):
         return "invalid_event_id"
     for k in ("path", "title"):
-        if ev.get(k) is not None and not isinstance(ev[k], str):
+        v = ev.get(k)
+        if v is not None and (not isinstance(v, str) or not _utf8_ok(v)):
             return "invalid_field_type"
     occ = ev.get("occurred_at")
     if not isinstance(occ, datetime):
@@ -75,15 +86,20 @@ def validate_event(ev) -> str | None:
         return "property_not_allowed"
     if not depth_ok:
         return "properties_depth"
-    # 体积按 UTF-8 字节数守门（汉字多字节，按字符数会被绕过）
-    if len(json.dumps(props, ensure_ascii=False, default=str).encode("utf-8")) > C.MAX_PROP_JSON_BYTES:
+    # 体积按 UTF-8 字节数守门（汉字多字节，按字符数会被绕过）；孤代理 encode 必炸，按 invalid 拒
+    try:
+        prop_bytes = len(json.dumps(props, ensure_ascii=False, default=str).encode("utf-8"))
+    except UnicodeEncodeError:
+        return "properties_invalid"
+    if prop_bytes > C.MAX_PROP_JSON_BYTES:
         return "properties_too_large"
     if str_too_long:
         return "properties_too_long"
+    # 先清洗后截断：urlencode 对中文查询参数最多膨胀 3 倍，先截后洗会破坏"出门 ≤MAX_PATH_LEN"不变量
+    if ev.get("path"):
+        ev["path"] = sanitize_url(ev["path"])
     if len(ev.get("path") or "") > C.MAX_PATH_LEN:
         ev["path"] = ev["path"][:C.MAX_PATH_LEN]
     if len(ev.get("title") or "") > C.MAX_TITLE_LEN:
         ev["title"] = ev["title"][:C.MAX_TITLE_LEN]
-    if ev.get("path"):
-        ev["path"] = sanitize_url(ev["path"])
     return None

server/tracker/tests/test_validation.py

@@ -17,8 +17,7 @@ def test_unknown_event_name():
     assert validate_event(_ev(event_name="xxx")) == "event_name_not_allowed"
 
 def test_sensitive_property_rejected():
-    r = validate_event(_ev(properties={"user_password": "1"}))
-    assert "sensitive" in r
+    assert validate_event(_ev(properties={"user_password": "1"})) == "sensitive_field"
 
 def test_shape_type_and_whitelist():
     assert validate_event(["x"]) == "event_invalid_shape"
@@ -26,14 +25,11 @@ def test_shape_type_and_whitelist():
     assert validate_event(_ev(properties={"foo": "bar"})) == "property_not_allowed"
 
 def test_too_many_props_and_long_string():
-    r = validate_event(_ev(properties={f"k{i}": "v" for i in range(40)}))
-    assert "properties" in r
-    r = validate_event(_ev(properties={"referrer": "x" * 600}))
-    assert "properties" in r
+    assert validate_event(_ev(properties={f"k{i}": "v" for i in range(40)})) == "properties_invalid"
+    assert validate_event(_ev(properties={"referrer": "x" * 600})) == "properties_too_long"
 
 def test_future_and_stale_time():
-    r = validate_event(_ev(occurred_at=NOW + timedelta(days=2)))
-    assert "occurred_at" in r                        # 超窗拒绝
+    assert validate_event(_ev(occurred_at=NOW + timedelta(days=2))) == "occurred_at_out_of_window"  # 超窗拒绝
     assert validate_event(_ev(occurred_at=NOW - timedelta(hours=2))) is None  # 窗内迟到可收
 
 def test_sanitize_url_drops_sensitive_params():
@@ -42,8 +38,7 @@ def test_sanitize_url_drops_sensitive_params():
     assert "monkey=1" in u          # fullmatch：含 key 子串的正常参数不误伤
 
 def test_nested_sensitive_key_rejected():
-    r = validate_event(_ev(properties={"utm": {"utm_a": 1, "user_password": "x"}}))
-    assert "sensitive" in r         # utm 在 page_view 白名单内，嵌套敏感键仍须命中
+    assert validate_event(_ev(properties={"utm": {"utm_a": 1, "user_password": "x"}})) == "sensitive_field"  # utm 在白名单内，嵌套敏感键仍须命中
 
 def test_naive_datetime_rejected():
     assert validate_event(_ev(occurred_at=NOW.replace(tzinfo=None))) == "invalid_occurred_at"
@@ -57,3 +52,19 @@ def test_nested_string_length_capped():
 
 def test_falsy_non_dict_properties_rejected():
     assert validate_event(_ev(properties=[])) == "properties_invalid"
+
+def test_lone_surrogate_event_id_rejected():
+    assert validate_event(_ev(event_id="\ud800")) == "invalid_event_id"
+
+def test_lone_surrogate_field_rejected():
+    assert validate_event(_ev(path="/p\ud800")) == "invalid_field_type"
+    assert validate_event(_ev(title="t\ud800")) == "invalid_field_type"
+
+def test_lone_surrogate_props_rejected():
+    assert validate_event(_ev(properties={"utm": {"a": "\ud800"}})) == "properties_invalid"
+
+def test_non_str_path_rejected():
+    assert validate_event(_ev(path=123)) == "invalid_field_type"
+
+def test_prop_depth_exceeded():
+    assert validate_event(_ev(properties={"utm": {"a": {"b": 1}}})) == "properties_depth"