fix: expose SessionValidationError.detail and fix test mypy types

Author: clean6378-max-it

models/errors.py

@@ -12,4 +12,5 @@ class SessionValidationError(ValueError):
 
     def __init__(self, path: str, detail: str) -> None:
         self.path = path
+        self.detail = detail
         super().__init__(f"Session validation failed at {path}: {detail}")

tests/test_jsonl_validation.py

@@ -2,6 +2,7 @@
 
 import os
 import sys
+from typing import Any
 
 import pytest
 
@@ -14,8 +15,8 @@
 FIXTURES = os.path.join(os.path.dirname(__file__), "fixtures")
 
 
-def _valid_payload(**overrides: object) -> dict:
-    base = {
+def _valid_payload(**overrides: Any) -> dict[str, Any]:
+    base: dict[str, Any] = {
         "session_id": "abc123",
         "title": "Test Session",
         "messages": [{"role": "user", "text": "hello"}],