fix: response validation returns 500 instead of 422 for nested schemas

[raunak-rpm]

Summary

Fixes #1659

When response validation fails on complex nested schemas (Tuples, Unions with Objects), the dynamic handler (aot: false) was returning 500 Internal Server Error instead of 422 Validation Error.

Root Cause

exact-mirror's Clean() function generates code that directly accesses nested properties without null checks. For example, it generates:

ar0p[1].file.ver.s

When called on invalid data (e.g., ver: null instead of ver: {s: '', m: null}), it throws a TypeError: null is not an object.

Solution

Wrap Clean() calls in try-catch in dynamic-handle.ts, consistent with how compose.ts (AOT mode) already handles this:

// compose.ts already does this for AOT mode:
`try{` +
`${name}=validator.${typeAlias}.Clean(${name})\n` +
`}catch{}`

Now dynamic-handle.ts does the same, making both modes consistent.

Changes

• src/dynamic-handle.ts: Wrap Clean() calls in try-catch blocks
• test/validator/response-validation-nested.test.ts: Add regression tests

Test Results

Scenario	Before	After
aot:false invalid nested response	❌ 500	✅ 422 with error details
aot:true invalid nested response	✅ 422	✅ 422
aot:false valid response	✅ 200	✅ 200
aot:true valid response	✅ 200	✅ 200
Full test suite (437 tests)	-	✅ 0 failures

Error Response Example

Now returns proper validation error with path and message:

{
  "type": "validation",
  "on": "response",
  "property": "/items/1/1/file/ver",
  "message": "Expected object",
  "errors": [...]
}

Summary by CodeRabbit

• Bug Fixes
  • Enhanced error handling for nested response validation, now returning proper 422 validation errors instead of 500 internal server errors when response validation fails.

_{✏️ Tip: You can customize this high-level summary in your review settings.}

[coderabbitai]

Walkthrough

This pull request adds defensive error handling around response validation Clean operations in the dynamic handler, wrapping them in try/catch blocks to gracefully handle Clean failures without cascading crashes. Additionally, a new test suite validates nested response schemas to ensure proper 422 validation errors for nested data mismatches.

Changes

Cohort / File(s)	Summary
Response Validation Error Handling src/dynamic-handle.ts	Introduces try/catch wrapping around response validator Clean calls in multiple code paths. Non-ValidationError exceptions from Clean are caught and converted to ValidationErrors; ValidationErrors are rethrown. Prevents cascading crashes on optional Clean transformation failures.
Nested Response Validation Tests test/validator/response-validation-nested.test.ts	New test suite with three tests covering nested response schema validation for both aot: false and aot: true modes. Validates that malformed nested responses return 422 status with proper validation error payloads instead of 500 errors.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~22 minutes

Possibly related PRs

• PR #1634: Modifies when Clean is created/applied for schemas with patternProperties in response validation, directly related to how Clean operations are handled in response validation logic.

Poem

🐰 Nested data danced with errors so deep,
Clean wrapped in shields now puts bugs to sleep.
Try-catch guards the validation way,
No more crashes to ruin the day!
Response schemas nestled safe and sound,
In 422 errors, sweet truth is found. 🛡️

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main change: wrapping Clean() calls in try-catch to fix response validation that was returning 500 instead of 422 for nested schemas.
Linked Issues check	✅ Passed	The PR directly addresses issue #1659 by wrapping Clean() calls in try-catch within src/dynamic-handle.ts to handle nested validation errors gracefully and return 422 instead of 500, plus adds comprehensive regression tests.
Out of Scope Changes check	✅ Passed	All changes are directly scoped to fixing the nested response validation issue: error handling in dynamic-handle.ts and regression tests in response-validation-nested.test.ts, with no unrelated modifications.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing touches

• 📝 Generate docstrings

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