fix(compiler): Make pluralization model optional when disabled

[ShashwatpSingh]

Problem

The PluralizationConfig type currently requires a model string even when enabled: false. This forces users to provide API keys and model configuration for a feature they're not using.

Current Behavior

• model is always required in PluralizationConfig
• PluralizationService constructor always initializes the AI model
• API keys are validated even when pluralization is disabled

Expected Behavior

• model should only be required when enabled: true
• Model should be lazy-initialized only when needed
• No unnecessary API calls when pluralization is disabled

Proposed Solution

1. Make model optional in PluralizationConfig: model?: string
2. Add runtime check: throw error if enabled: true but no model
3. Move model initialization from constructor to generateBatch() method

Benefits

• Better DX: Users don't need to configure unused features
• Performance: No unnecessary model initialization
• Resource efficiency: No API key validation when not needed
• Cleaner config: Only required fields when disabled

[sourabhmahato]

Hi! I'd like to work on this issue. I noticed the previous PR #1982 was closed due to assignment — I'd like to pick this up if available. Could you please assign it to me?

I've already forked the repo and dug into the codebase. Here's my proposed approach after reviewing the source:

Root Cause:
In types.ts, PluralizationConfig defines model as a required string, even though it's only needed when enabled: true. This forces users to supply a model string (and by extension, valid API keys) even when pluralization is disabled.

Meanwhile in translation-service.ts, PluralizationService is already conditionally created only when enabled is true — so the service-level guard exists, but the type doesn't reflect that.

Proposed Changes:

1. types.ts — Make model optional:

export type PluralizationConfig = {
  sourceLocale: LocaleCode;
  enabled: boolean;
  model?: string; // only required when enabled: true
};

2. service.ts — Add a runtime guard in the PluralizationService constructor to throw a clear error if enabled: true but model is missing:

constructor(config: PluralizationConfig, private logger: Logger) {
  if (!config.model) {
    throw new Error(
      'Pluralization model is required when pluralization is enabled. ' +
      'Provide a model string (e.g., "groq:llama3-8b-8192") in your config.'
    );
  }
  // ... existing logic
}

3. types.ts (compiler config) — Update PartialPluralizationConfig to keep the types consistent.

4. Tests — Add unit tests covering:

   • Config validation passes when enabled: false without model
   • Config validation passes when enabled: true with a valid model
   • Runtime error thrown when enabled: true but model is missing

This is a surgical change — the TranslationService already guards against creating PluralizationService when disabled (line 105), so making model optional at the type level simply aligns the type contract with the runtime behavior.