feat(agent): form pipeline + collection prompt workflow@20261021

- merge main: workflow/20261021 (collection prompt adds step-5 mandatory
  time readback-confirm before routing; non-motor/0003 branch rework;
  accident_cause unified schema), updated eval suites (photo_skip/
  button_guidance rewritten, no_false trimmed to asr, new
  non_motor_vehicle + time_confirmation with form/reply assertions),
  runner gains form/formMatches/replyMatches expectations
- prompts/collection.md regenerated from 20261021; extraction prompt
  archived (contentExtract description, 6-key whitelist)
- collect: extraction call per turn (extraction.md + current time/form
  injected), merge follows 更新表单 semantics (meaningful values only,
  number/string equality, diff -> turn_patch); accident_fields now uses
  external form keys
- backend: form_update flows to ChatResult and SSE formUpdate event
  (stream emits prefix, FormUpdate, body)
- fields: FORM_FIELDS whitelist with strict type validation
- verified: 155 unit tests; golden evals on real model - photo_skip 4/4,
  no_false 2/2, photo_button_guidance 12/12, non_motor_vehicle 14/14,
  collection_skip 10/12, time_confirmation 1/2; remaining 3 failures are
  model sequence/literal-template adherence, recorded in plan appendix

src/agent/fields.py

@@ -16,7 +16,7 @@ from .clock import Clock, SystemClock, validate_accident_time
 
 ACCIDENT_FIELD_KEYS = (
     "ywrysw", "ywfjdc", "ywmtc", "bjrjs",
-    "sgfssj", "sfsgxc", "jdcsl", "sgyy",
+    "sgfssj", "sfsgxc", "jdcsl", "sgyy", "accident_cause",
 )
 PERSON1_FIELD_KEYS = (
     "xm1", "hpzl1", "hphm1", "sfzmhm1", "sfzmwh1", "sjhm1", "sjwh1", "csbw1",
@@ -28,6 +28,35 @@ KNOWN_FIELD_KEYS = frozenset(
     ACCIDENT_FIELD_KEYS + PERSON1_FIELD_KEYS + PERSON2_FIELD_KEYS
 )
 
+# 事故表单字段（来源：workflow@20261021「文本内容提取事故信息」白名单 +
+# 「更新表单」code 节点的差量合并语义）
+FORM_FIELDS: dict[str, type] = {
+    "has_injury": bool,
+    "has_non_motor_vehicle_hit": bool,
+    "is_on_scene": bool,
+    "vehicle_count": int,
+    "accident_time": str,
+    "accident_cause": str,
+}
+
+
+def validate_form_update(data: dict) -> dict:
+    """按白名单与类型校验提取输出；非法键/类型丢弃（对应更新表单的忽略语义）。"""
+    validated = {}
+    for key, value in (data or {}).items():
+        spec = FORM_FIELDS.get(key)
+        if spec is None:
+            continue
+        if spec is bool and not isinstance(value, bool):
+            continue  # 布尔字段严格 bool，不接受 0/1/字符串
+        if spec is int and (isinstance(value, bool) or not isinstance(value, int)):
+            continue
+        if spec is str and not isinstance(value, str):
+            continue
+        validated[key] = value
+    return validated
+
+
 TIME_FIELDS = frozenset({"sgfssj"})  # 事故发生时间：需时间校验
 
 # 布尔语义字段：明确肯定/否定之外（模糊、ASR 破碎）不得猜测。