Null-Safety Guards, Readonly Schema Support & Upstream v2.0.0 Alignment

Executive Summary

This pull request brings @bufferpunk/modelcore up to enterprise-grade stability (v2.0.0). It addresses runtime null-pointer vulnerabilities, string character-splitting in Union types, readonly schema enum support for as const arrays, defensive input sanitization, and full synchronization with the upstream modular src/ architecture.

1. Summary of Changes & Technical Explanations

A. Readonly Array Support for Enum Definitions (src/typing.d.ts & src/typing.ts)

• Problem: When model schemas declared enum values using as const assertions (readonly string[]) or frozen arrays (Object.freeze([...])), the TypeScript compiler threw strict type errors (TS2530/TS4104) because FieldConfig.enum strictly expected a mutable any[].
• Before (Failed Typecheck):

  const ROLES = ["ADMIN", "USER", "GUEST"] as const; // Readonly array
  
  class User extends Base {
    static override get schema() {
      return {
        role: { type: String, enum: ROLES } // TS Error: Type 'readonly ["ADMIN", "USER", "GUEST"]' is not assignable to 'any[]'
      };
    }
  }

• After (Fixed Interface):

  export interface FieldConfig {
    // ...
    enum?: any[] | readonly any[]; // Supports both mutable and immutable readonly arrays
  }

• Code Example (Usage):

  import { Base, SchemaDefinition } from "@bufferpunk/modelcore";
  
  const ROLES = ["ADMIN", "USER", "GUEST"] as const;
  
  export class User extends Base {
    static override get schema(): SchemaDefinition {
      return {
        role: { type: String, enum: ROLES }
      } as const satisfies SchemaDefinition;
    }
  }
  
  const u = new User({ role: "ADMIN" }); // Validates cleanly with 100% type safety

B. Defensive Null & Degenerate Schema Guarding (src/utils.ts & src/base.ts)

• Problem: Passing non-function types ({ type: undefined }, { type: null }, or { type: "string" }) into field configs resulted in raw Node.js runtime crashes: TypeError: Cannot read properties of undefined (reading 'prototype').
• Before (Runtime Crash):

  class Product extends Base {
    static schema = { title: { type: undefined } };
  }
  
  new Product({ title: "Laptop" }); 
  // Unhandled Exception: TypeError: Cannot read properties of undefined (reading 'prototype')

• After (Structured Error Guard):

  // Validation guard in normalizeConf
  if (typeof conf.type !== "function") {
    throw new SchemaDefinitionError(
      `Invalid schema definition for key '${key}': type must be a constructor function`
    );
  }

• Behavior After Fix:

  new Product({ title: "Laptop" }); 
  // Throws structured SchemaDefinitionError with code 'SCHEMA_DEFINITION_ERROR'

C. Null-Prototype Input Protection (Object.create(null))

• Problem: Objects created via Object.create(null) lack Object.prototype methods and .constructor. Passing them as inputs triggered unhandled exceptions during isOfType() property lookups.
• Before:

  class User extends Base { static schema = { name: String }; }
  const nullProtoObj = Object.create(null);
  nullProtoObj.name = "Alice";
  
  new User(nullProtoObj); // Crashed with TypeError: Cannot read properties of null

• After:

  const nullProtoObj = Object.create(null);
  nullProtoObj.name = "Alice";
  
  const user = new User(nullProtoObj); // Safely constructs and extracts properties

D. Union Type Structural Discrimination (src/typing.ts & src/utils.ts)

• Problem: Passing a scalar string to a Union(Array, String) field caused the string to enter the Array iteration block, converting "hello" into ['h','e','l','l','o']. Passing a string to Union(Object, String) evaluated object key rules against string properties.
• Before (Data Corruption):

  class Event extends Base {
    static schema = { payload: { type: Union(Array, String), values: String } };
  }
  
  const ev = new Event({ payload: "hello" });
  console.log(ev.payload); // Output: ['h', 'e', 'l', 'l', 'o'] (String corrupted into char array)

• After (Type Safety Guard):

  // Enforces structural type check before executing array/object validation handlers
  if (conf.type === Array && !Array.isArray(value)) {
    return false; // Safely skip Array branch and fallback to String branch
  }

• Result:

  const ev = new Event({ payload: "hello" });
  console.log(ev.payload); // Output: "hello" (Preserved as primitive string)

2. Upgrade & Migration Notes (v1.x -> v2.0.0)

1. Named Import Update:

   // ❌ Old: import Base from "@bufferpunk/modelcore";
   // ✅ New: import { Base } from "@bufferpunk/modelcore";

2. TypeScript Inheritance Modifier:

   // ✅ Recommended: Use static override get schema()
   class Model extends Base {
     static override get schema(): SchemaDefinition { ... }
   }

3. Verification & Testing

• Executed unit test suite:

  npm test

• Outcome: 62 / 62 unit tests passing cleanly (0 failures).