feat(swift_core): Establish JSON identity routing and evaluation protocols

[pinieb]

Description

Overview

This PR establishes the foundational skeleton for the JSON Schema evaluation engine. It introduces the core data structures needed to deterministically identify nodes in the schema tree and defines the strict execution contracts required to safely evaluate JSON instances against those nodes.

By separating identity resolution from execution state, this PR paves the way for the SchemaCompiler and the implementation of specific validation keywords without risking tight coupling or infinite recursion loops.

Key Additions

1. Identity & Routing (RFC 6901)

• JSONPointer: Implemented a robust path management struct fully compliant with RFC 6901, including proper escaping and unescaping of ~0 and ~1 characters.
• SchemaIdentity: Created a deterministic identity pairing a Base URI with a JSON Pointer. Crucially, this includes the updatingBaseURI logic necessary to intercept $id keywords, allowing schemas to safely reset their resolution scope and pointer paths during compilation.

2. Execution Contracts

• KeywordEvaluator: Defined the primary protocol that all future validators, applicators, and annotators will conform to.
• SchemaNode: Implemented the compiled AST node representation. It holds an array of KeywordEvaluators and handles the aggregation of errors and annotations during evaluation.
• ValidationResult: Designed to fully support the 2020-12 hierarchical/verbose output format, tracking isValid, errors, annotations, and deeply nested child results.

3. Context & State Management

• ValidationContext: Introduced the immutable state container passed down during tree traversal.
• ValidatorConfiguration: Added standard user configurations, including maxEvaluationDepth to defend against stack overflows from infinitely recursive malicious schemas.

Technical Notes

• Recursion Defense: ValidationContext.passingDown(toInstanceKey:) actively tracks execution depth and will throw a hard error if the configured limit is breached.
• Immutability: The execution lifecycle remains strictly non-mutating. Context updates and identity mutations are handled via copying value types (Swift structs) to maintain thread safety and prevent shared-state side effects.

Testing

• Added coverage for RFC 6901 character escaping and path appending.
• Added coverage for Base URI resets (simulating the behavior of $id).
• Added coverage for Context max-depth throwing.
• Verified SchemaNode successfully aggregates multiple keyword results (combining discrete annotations and errors into a single ValidationResult).

Pre-launch Checklist

For this PR:

• I have added updates to the [CHANGELOG].
• I updated/added relevant documentation.
• My code changes (if any) have tests.
• If my branch is on fork, I have verified that scripts/e2e_test.sh passes.
  • Used run_tests.sh for Swift tests

[gemini-code-assist]

Code Review

This pull request sets up the A2UISwiftCore package and implements the core types for the generic JSONSchema validator target, including JSONValue, JSONPointer, SchemaIdentity, and SchemaNode, along with comprehensive unit tests and documentation. The review feedback highlights several key improvements: making the JSONPointer string initializer failable to handle malformed paths safely, conforming both JSONPointer and SchemaIdentity to Hashable for collection and dictionary compatibility, normalizing baseURI in SchemaIdentity to prevent double-fragment URIs, and ensuring compliance with the JSON Schema Draft 2020-12 specification by discarding annotations when validation fails.