Modernize Gemini models and add comprehensive error handling with testing

.gitignore

@@ -34,7 +34,7 @@ Thumbs.db
 *.sw?
 
 # Optional backend venv (if created in root)
-#.venv/ 
+#.venv/
 
 # Byte-compiled / optimized / DLL files
 __pycache__/
@@ -199,4 +199,4 @@ cython_debug/
 #  option (not recommended) you can uncomment the following to ignore the entire idea folder.
 #.idea/
 
-backend/.langgraph_api
+backend/.langgraph_api

.pre-commit-config.yaml

@@ -0,0 +1,76 @@
+# Pre-commit configuration for Gemini LangGraph Quickstart
+# See https://pre-commit.com for more information
+
+repos:
+  # Model Validation (Critical - prevents 404 model errors)
+  - repo: local
+    hooks:
+      - id: model-validation
+        name: Model Configuration Validation
+        entry: ./tests/test-model-validation.sh
+        language: script
+        always_run: true
+        pass_filenames: false
+        description: "Prevent frontend/backend model mismatches that cause 404 errors"
+
+  # Backend Python (Ruff - modern all-in-one tool)
+  - repo: local
+    hooks:
+      - id: ruff-lint
+        name: Ruff Linting (Python)
+        entry: bash -c 'cd backend && ruff check --fix .'
+        language: system
+        files: ^backend/.*\.py$
+        description: "Fast Python linter (replaces flake8, isort, etc.)"
+      - id: ruff-format
+        name: Ruff Format (Python)
+        entry: bash -c 'cd backend && ruff format .'
+        language: system
+        files: ^backend/.*\.py$
+        description: "Fast Python formatter (replaces black)"
+
+  # Frontend TypeScript/React
+  - repo: local
+    hooks:
+      - id: eslint-frontend
+        name: ESLint (Frontend)
+        entry: bash -c 'cd frontend && npm run lint'
+        language: system
+        files: ^frontend/.*\.(ts|tsx|js|jsx)$
+        description: "TypeScript/React linting"
+      - id: prettier-frontend
+        name: Prettier (Frontend)
+        entry: bash -c 'cd frontend && npm run format'
+        language: system
+        files: ^frontend/.*\.(ts|tsx|js|jsx|json|css|md)$
+        description: "Frontend code formatting (auto-fix)"
+      - id: typescript-check
+        name: TypeScript Check
+        entry: bash -c 'cd frontend && npx tsc --noEmit'
+        language: system
+        files: ^frontend/.*\.(ts|tsx)$
+        description: "TypeScript type checking"
+
+  # General file hygiene
+  - repo: https://github.com/pre-commit/pre-commit-hooks
+    rev: v5.0.0
+    hooks:
+      - id: check-yaml
+        name: Check YAML
+        description: "Validate YAML syntax"
+      - id: check-json
+        name: Check JSON
+        description: "Validate JSON syntax"
+      - id: trailing-whitespace
+        name: Trim Trailing Whitespace
+        description: "Remove trailing whitespace"
+      - id: end-of-file-fixer
+        name: Fix End of Files
+        description: "Ensure files end with newline"
+      - id: check-merge-conflict
+        name: Check Merge Conflicts
+        description: "Check for merge conflict markers"
+
+# Global settings
+default_install_hook_types: [pre-commit]
+default_stages: [pre-commit]

Makefile

@@ -17,4 +17,4 @@ dev-backend:
 # Run frontend and backend concurrently
 dev:
 	@echo "Starting both frontend and backend development servers..."
-	@make dev-frontend & make dev-backend 
+	@make dev-frontend & make dev-backend

README.md

@@ -16,10 +16,11 @@ This project demonstrates a fullstack application using a React frontend and a L
 
 ## Project Structure
 
-The project is divided into two main directories:
+The project is divided into main directories:
 
 -   `frontend/`: Contains the React application built with Vite.
 -   `backend/`: Contains the LangGraph/FastAPI application, including the research agent logic.
+-   `tests/`: Contains project-wide regression tests for model validation and configuration consistency.
 
 ## Getting Started: Development and Local Testing
 
@@ -84,6 +85,25 @@ cd backend
 python examples/cli_research.py "What are the latest trends in renewable energy?"
 ```
 
+## Testing
+
+Run comprehensive model validation tests to ensure frontend/backend model consistency:
+
+```bash
+./tests/test-model-validation.sh
+```
+
+These regression tests prevent model configuration mismatches that can cause 404 errors and application crashes. See `tests/README.md` for detailed testing documentation.
+
+### Pre-commit Hooks
+
+Set up automated code quality checks that run before each commit:
+
+```bash
+./setup-precommit.sh
+```
+
+This configures hooks for model validation, Python linting (Ruff), frontend formatting (Prettier), and TypeScript checking.
 
 ## Deployment
 
@@ -117,4 +137,4 @@ Open your browser and navigate to `http://localhost:8123/app/` to see the applic
 
 ## License
 
-This project is licensed under the Apache License 2.0. See the [LICENSE](LICENSE) file for details. 
+This project is licensed under the Apache License 2.0. See the [LICENSE](LICENSE) file for details.

backend/.env.example

@@ -1 +1 @@
-# GEMINI_API_KEY=
+# GEMINI_API_KEY=

backend/Makefile

@@ -61,4 +61,3 @@ help:
 	@echo 'tests                        - run unit tests'
 	@echo 'test TEST_FILE=<test_file>   - run all tests in file'
 	@echo 'test_watch                   - run unit tests in watch mode'
-

backend/examples/cli_research.py

@@ -1,5 +1,7 @@
 import argparse
+
 from langchain_core.messages import HumanMessage
+
 from agent.graph import graph
 
 
@@ -21,7 +23,7 @@ def main() -> None:
     )
     parser.add_argument(
         "--reasoning-model",
-        default="gemini-2.5-pro-preview-05-06",
+        default="gemini-2.5-pro",
         help="Model for the final answer",
     )
     args = parser.parse_args()

backend/src/agent/app.py

@@ -1,5 +1,6 @@
 # mypy: disable - error - code = "no-untyped-def,misc"
 import pathlib
+
 from fastapi import FastAPI, Response
 from fastapi.staticfiles import StaticFiles
 

backend/src/agent/configuration.py

@@ -1,8 +1,8 @@
 import os
-from pydantic import BaseModel, Field
-from typing import Any, Optional
+from typing import Any
 
 from langchain_core.runnables import RunnableConfig
+from pydantic import BaseModel, Field
 
 
 class Configuration(BaseModel):
@@ -41,7 +41,7 @@ class Configuration(BaseModel):
 
     @classmethod
     def from_runnable_config(
-        cls, config: Optional[RunnableConfig] = None
+        cls, config: RunnableConfig | None = None
     ) -> "Configuration":
         """Create a Configuration instance from a RunnableConfig."""
         configurable = (