Enhance JSON schema validation with contextual suggestions for fixes

[Copilot]

This PR significantly improves the developer experience when encountering JSON schema validation errors by providing contextual suggestions for fixes.

Problem

Previously, schema validation errors provided only generic messages that didn't help users understand what valid alternatives were available:

Unknown property: invalid_property
got string, want integer

This made it difficult for users to quickly fix validation errors, especially when dealing with typos or unfamiliar properties in complex nested configurations.

Solution

The validation system now analyzes the JSON schema to provide intelligent suggestions:

Field Name Suggestions

When users provide invalid property names, the system extracts valid field names from the schema and suggests close matches:

Unknown property: timeout_minuts. Did you mean one of: timeout_minutes, ...
Unknown property: unknown_permission. Did you mean one of: actions, attestations, checks, contents, deployments, discussions, id-token, issues, ...

Type Error Examples

When the wrong data type is provided, the system generates example JSON showing the correct format:

got string, want integer. Expected format: 42

Multiple Error Handling

The system can handle multiple validation errors and provide comprehensive suggestions:

Unknown properties: permision, timeout_minuts. Valid fields are: permissions, on, description, timeout_minutes, safe-outputs

Key Features

• Smart similarity matching: Uses heuristic scoring to find the closest field name matches
• Schema-aware suggestions: Automatically extracts valid properties from complex JSON schemas
• Nested object support: Properly handles oneOf schemas and deeply nested configurations
• Example JSON generation: Creates realistic examples based on schema definitions
• Performance optimized: Early returns and efficient similarity calculations
• Backward compatible: All existing error handling preserved

Technical Implementation

The implementation adds several new functions to pkg/parser/schema.go:

• generateSchemaBasedSuggestions(): Main entry point for generating contextual suggestions
• extractAcceptedFieldsFromSchema(): Navigates JSON schema to find valid properties
• generateFieldSuggestions(): Creates human-readable field suggestions with similarity matching
• generateExampleJSONForPath(): Generates example JSON objects from schema definitions
• resolveSchemaWithOneOf(): Handles complex oneOf schema patterns correctly

All magic numbers have been extracted as named constants, and comprehensive test coverage ensures reliability across different validation scenarios.

Impact

This change transforms validation errors from cryptic messages into actionable guidance, significantly reducing the time developers spend debugging configuration issues in agentic workflows.

Original prompt

Update the rendering of json schema validation by providing suggestions for fixes based on the schema.

• if a field name is unexpected, suggest accept fields
• if the wrong object type is provided, show example of correct JSON (generated on the fly from the schema)

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