feat(v3): implement schema discovery endpoint

app/routers/api_crud_v3.py

@@ -96,6 +96,84 @@ async def health_check(
     return mk_resp(data={"status": "V3 API is healthy!"})
 
 
+@router.get("/{obj_type}/schema", response_model=Resp_Body_Base, tags=['CRUD v3 Schema (Dev)'])
+async def get_obj_schema(
+        response: Response,
+        obj_type: str = Path(min_length=2, max_length=50),
+        view: str = Query('default', description="Select alternative view/model (e.g., enriched, detail)"),
+        variant: str = Query('base', regex='^(base|in|out|default)$', description="Select model variant"),
+        account: AccountContext = Depends(get_account_context),
+        ):
+    """
+    Returns the schema for a specific Aether object type.
+    Combines database column metadata with Pydantic model field definitions.
+    """
+    from app.db_sql import db
+    from sqlalchemy import text
+
+    if obj_type not in obj_type_kv_li:
+        return mk_resp(data=False, status_code=400, response=response, status_message=f"Object type '{obj_type}' not found.")
+
+    obj_cfg = obj_type_kv_li[obj_type]
+    
+    # Select table/view
+    table_name = obj_cfg.get(f'tbl_{view}', obj_cfg.get('tbl_default', obj_cfg.get('tbl')))
+    
+    # Select model variant
+    model_key = f'mdl_{variant}' if variant != 'base' else 'mdl'
+    model = obj_cfg.get(model_key, obj_cfg.get('mdl_default', obj_cfg.get('mdl')))
+
+    if not table_name:
+        return mk_resp(data=False, status_code=500, response=response, status_message=f"Table configuration for '{obj_type}' is missing.")
+
+    schema_info = {
+        "object_type": obj_type,
+        "view": view,
+        "variant": variant,
+        "database": {
+            "table_name": table_name,
+            "columns": []
+        },
+        "model": {
+            "name": model.__name__ if hasattr(model, '__name__') else str(model),
+            "fields": {}
+        }
+    }
+
+    # 1. Get Database Metadata
+    try:
+        db_result = db.execute(text(f"DESCRIBE `{table_name}`"))
+        for row in db_result.fetchall():
+            schema_info["database"]["columns"].append({
+                "field": row[0],
+                "type": row[1],
+                "nullable": row[2] == 'YES',
+                "key": row[3],
+                "default": row[4],
+                "extra": row[5]
+            })
+    except Exception as e:
+        log.warning(f"Failed to describe table '{table_name}': {e}")
+        schema_info["database"]["error"] = str(e)
+
+    # 2. Get Pydantic Model Metadata
+    if model and hasattr(model, "__fields__"):
+        for field_name, field in model.__fields__.items():
+            field_info = {
+                "alias": field.alias,
+                "type": str(field.outer_type_),
+                "required": field.required,
+                "default": field.default
+            }
+            # Include extra metadata from Field() if present
+            if field.field_info.description:
+                field_info["description"] = field.field_info.description
+            
+            schema_info["model"]["fields"][field_name] = field_info
+
+    return mk_resp(data=schema_info, response=response)
+
+
 # --- TOP LEVEL OBJECTS ---
 
 @router.get('/{obj_type_l1}/{obj_id}', response_model=Resp_Body_Base)