Enhance V3 CRUD: Implement Error Bubbling and Dry-Run Validation.

- Updated app/db_sql.py to capture SQL exceptions in thread-local storage for later retrieval.
- Implemented format_db_error() in app/lib_api_crud_v3.py to clean up raw MariaDB error strings.
- Added POST /v3/crud/{obj_type}/validate endpoint for dry-run payload validation.
- Updated main and nested routers to bubble up validation and database errors into the response 'meta.details' field.
- Added tests/test_v3_error_bubbling.py to verify formatting logic.

app/db_sql.py

@@ -1,4 +1,4 @@
-import datetime, json, pytz, random, redis, secrets
+import datetime, json, pytz, random, redis, secrets, threading
 from typing import Any, List, Optional
 from timeit import default_timer as timer
 
@@ -10,6 +10,19 @@ from sqlalchemy import create_engine, text, Time
 from sqlalchemy.exc import IntegrityError, OperationalError, ProgrammingError
 from sqlalchemy.pool import NullPool
 
+# Thread-local storage for capturing last SQL error message
+_sql_error_state = threading.local()
+
+def get_last_sql_error() -> Optional[str]:
+    """Retrieves and clears the last captured SQL error message."""
+    error = getattr(_sql_error_state, 'last_error', None)
+    _sql_error_state.last_error = None
+    return error
+
+def set_last_sql_error(error: Any):
+    """Sets the last captured SQL error message."""
+    _sql_error_state.last_error = str(error)
+
 from app.lib_sql_search import (
     sql_limit_offset_part as _sql_limit_offset_part,
     sql_and_like_part as _sql_and_like_part,
@@ -114,11 +127,13 @@ def sql_insert(
         trans.rollback()
         log.error('Integrity error (likely duplicate). Returning None')
         log.debug(e)
+        set_last_sql_error(e)
         return None
     except Exception as e:
         trans.rollback()
         log.error('Unknown exception in sql_insert. Returning False')
         log.exception(e)
+        set_last_sql_error(e)
         return False
     else:
         if result_insert.rowcount == 1 and result_insert.lastrowid > 0:
@@ -186,11 +201,13 @@ def sql_update(
         try:
             result_update = db.execute(sql_update_stmt, data)
             trans.commit()
-        except Exception:
+        except Exception as e:
+            set_last_sql_error(e)
             return False
     except Exception as e:
         trans.rollback()
         log.exception(e)
+        set_last_sql_error(e)
         return False
     else:
         if result_update.rowcount >= 1: