[BUG]: Exception handlers registered but never attached to the FastAPI app

[GaneshPatil7517]

⚡️ Describe the Bug

The custom exception handler for AppError is defined in handlers.py via the register_exception_handlers(app) function, but this function is never called anywhere in the application. In main.py, the FastAPI app is created and routers are included, but the exception handlers are never attached:

# api/main.py (current)
from fastapi import FastAPI
from api.routes import templates, forms

app = FastAPI()

app.include_router(templates.router)
app.include_router(forms.router)
# ❌ register_exception_handlers(app) is never called

This means when AppError is raised (e.g., in forms.py line 15 when a template is not found), FastAPI does not know how to handle it and returns a generic 500 Internal Server Error instead of the intended structured JSON error response.

# api/routes/forms.py — this raise will result in a 500, not a 404
if not get_template(db, form.template_id):
    raise AppError("Template not found", status_code=404)

👣 Steps to Reproduce

1. Clone the repo and install dependencies (pip install -r requirements.txt)
2. Initialize the database: python -m api.db.init_db
3. Start the API server: uvicorn api.main:app --reload
4. Send a POST request to /forms/fill with a non-existent template_id:

curl -X POST http://localhost:8000/forms/fill \
  -H "Content-Type: application/json" \
  -d '{"template_id": 9999, "input_text": "test"}'

5. Observe a 500 Internal Server Error instead of a 404 JSON response.

📉 Expected Behavior

The API should return a clean JSON error response with the correct status code:

{
  "error": "Template not found"
}

with HTTP status 404, as designed in handlers.py

🖥️ Environment Information

OS: Windows 11 / Ubuntu 22.04 (reproducible on any OS)
Python: 3.11+ (also tested on 3.13)
Docker/Compose Version: N/A (reproducible without Docker)
Ollama Model used: N/A (bug is in API layer, not LLM)

📸 Screenshots/Logs

Server log output when hitting the endpoint with an invalid template ID:
INFO: 127.0.0.1:xxxxx - "POST /forms/fill HTTP/1.1" 500 Internal Server Error

The traceback shows an unhandled AppError exception because no handler is registered.

🕵️ Possible Fix

Import and call register_exception_handlers(app) in main.py:

from fastapi import FastAPI
from api.routes import templates, forms
from api.errors.handlers import register_exception_handlers

app = FastAPI()

register_exception_handlers(app)

app.include_router(templates.router)
app.include_router(forms.router)

[GaneshPatil7517]

Hello @juanalvv Sir
I have opened Issue #82 describing the problem with exception handlers not being attached to the FastAPI application. After investigating the codebase, I identified the root cause and validated a potential fix locally.
May I proceed with submitting a Pull Request for this issue? Please let me know if there are any preferred implementation details, coding standards, or additional checks you would like me to follow before opening the PR.
Thank you for your guidance....