feat: enhance error handling and validation responses

[moutonjeremy]

• Introduced custom error handlers for not found and default error shapes.
• Updated OpenAPI spec generation to include custom error types and schemas.
• Changed validation error responses from 400 to 422 to align with RESTful standards.
• Enhanced error envelope structure to provide detailed validation error information.
• Updated tests to reflect new status codes and error handling behavior.

[Copilot]

Pull request overview

This PR upgrades the library’s default error handling to emit a structured ErrorEnvelope, shifts validation failures to 422 Unprocessable Entity, adds an opt-in not-found catch-all handler (404/405), and enhances OpenAPI generation to document both default envelopes and per-route custom error shapes.

Changes:

• Introduce ErrorEnvelope / ValidationErrorEntry with request correlation metadata and richer per-field validation output.
• Add UseNotFoundHandler() + Config.NotFoundHandler and update OpenAPI generation to include 404 (when installed) plus default 400/422 examples.
• Add per-operation OpenAPIOptions.Errors to generate concrete status-code responses and schemas; update tests/docs accordingly.

Reviewed changes

Copilot reviewed 21 out of 23 changed files in this pull request and generated 8 comments.

Show a summary per file

File	Description
validation_test.go	Updates expected validation status codes to 422 and asserts the new envelope shape.
types.go	Adds new config knobs (not found + default error shape), and introduces the ErrorEnvelope types.
time_type_test.go	Adjusts spec assertions to expect custom TError under the 4XX response key.
README.md	Documents the new envelope, status codes, not-found handler, and DefaultErrorShape behavior.
put_test.go	Updates PUT validation expectations to 422 and checks envelope/parse error categorization.
post_test.go	Updates POST validation expectations to 422 and checks envelope/parse error categorization.
json_type_error_test.go	Updates expectations to categorize JSON type mismatches as type_error.
header_params_test.go	Updates header validation status to 422.
get_oapi_test.go	Updates GET/query validation expectations to 422.
fiberoapi.go	Implements new default error behavior, adds OpenAPI error response generation + per-route custom error responses.
error_response.go	New implementation for envelope building, request-id/path sanitization, and not-found/405 handling utilities.
error_envelope_test.go	New tests validating envelope shape, request-id behavior, not-found handler behavior, and OpenAPI examples.
delete_test.go	Updates DELETE validation expectations to 422.
default_error_shape_test.go	New tests for DefaultErrorShape behavior at runtime and in generated OpenAPI.
custom_validation_error_test.go	Updates default validation behavior tests to match 422 + envelope output.
custom_errors.go	New helpers for extracting status/description/schema for declared per-route custom errors.
custom_errors_test.go	New tests for per-route error declarations, schema deduplication, and runtime emission.
coverage_test.go	Adds focused tests to improve coverage on helper branches and docs endpoints.
common.go	Uses wrapped JSON type errors; hardens isZero against nil error interfaces; removes old mismatch detection helpers.
_examples/simple_error/main.go	Adds a new example demonstrating per-route errors + DefaultErrorShape.
_examples/simple_error/go.mod	Example module setup (with replace) for running the example locally.
_examples/simple_error/go.sum	Example dependency lockfile.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

Pull request overview

Copilot reviewed 22 out of 24 changed files in this pull request and generated 6 comments.