Parameter and exception handling enhancements

[rkritika1508]

Summary

Target issue is #14.
Explain the motivation for making this change. What existing problem does the pull request solve?
Fixing three things in this PR, all related to parameter validation and exception handling -

1. While the post endpoints gives back error for wrong parameter value, it's formatting can be better.
   "error": "Invalid field(s): inputs (Extra inputs are not permitted)"
2. It also does not give any error for wrong parameter name added with validators.
   "error": "Invalid field(s): validators.0.uli_slur_match.on_pass (Extra inputs are not permitted)"
3. The error you get for missing input body is not very clear as of now.
   "error": "Missing required field(s): input."

Checklist

Before submitting a pull request, please ensure that you mark these task.

• Ran fastapi run --reload app/main.py or docker compose up in the repository root and test.
• If you've fixed a bug or added code that is tested and has test cases.

Notes

Please add here if any other information is required for the reviewer.

Summary by CodeRabbit

• Bug Fixes
  • Enhanced error messaging when validation fails, providing clearer feedback on missing or invalid fields.
  • API now enforces stricter validation, rejecting requests containing unexpected fields for improved data integrity.

[coderabbitai]

📝 Walkthrough

Walkthrough

These changes enhance validation error handling with a new helper function that formats validation errors into readable messages, while standardizing Pydantic model configurations across the codebase using ConfigDict for consistency.

Changes

Cohort / File(s)	Summary
Validation Error Formatting backend/app/core/exception_handlers.py	Introduces _format_validation_errors() helper function to convert RequestValidationError details into human-readable messages. Updates validation_error_handler to use formatted error output with APIResponse.failure_response().
Model Configuration Standardization backend/app/models/base_validator_config.py, backend/app/models/guardrail_config.py	Adds ConfigDict import from pydantic and updates model configurations. BaseValidatorConfig now uses ConfigDict(extra="forbid", arbitrary_types_allowed=True). GuardrailRequest adds ConfigDict(extra="forbid") to enforce strict field validation.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

Poem

🐰 Errors now speak with clarity and grace,
ConfigDicts put each model in its place,
Forbidding extras with a gentle touch,
Validation flows so smoothly—oh, how much! ✨

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The PR title accurately describes the main changes: it introduces error message formatting improvements and adds stricter parameter validation (extra field forbidding) across multiple handler and model files.

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✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch feat/parameter-exception-enhancements

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[coderabbitai]

Actionable comments posted: 1

🤖 Fix all issues with AI agents

In `@backend/app/core/exception_handlers.py`:
- Around line 11-40: The _format_validation_errors function can return an empty
string when all error entries are filtered out (e.g., top-level loc=("body",)),
producing an empty message; update _format_validation_errors to detect when the
resulting messages list is empty and return a sensible fallback like "Invalid
request body" (or similar) so callers always get a non-empty error message; keep
existing logic (loc filtering, missing_fields, invalid_fields) and only add the
fallback return when messages is empty before returning.

🧹 Nitpick comments (1)

backend/app/core/exception_handlers.py (1)

15-16: Potential KeyError if an error dict lacks "loc" or "msg" keys.

The code accesses err["loc"] (Line 16) and err["msg"] (Line 23) without .get() fallbacks. While Pydantic's RequestValidationError.errors() should always include these keys, defensive access would make this more robust against unexpected error shapes (e.g., from custom validators).