fix [name, options] syntax for transformers registered as instances

[gigi206]

Problem

The configuration syntax "use": [["TransformerName", { ...options }]] is documented for passing options to a transformer constructor, and the built-in AnthropicTransformer exposes a UseBearer option through its constructor:

constructor(private readonly options?: TransformerOptions) {
  this.useBearer = this.options?.UseBearer ?? false;
}

However, attempting to use it from config:

{
  "transformer": { "use": [["Anthropic", { "UseBearer": true }]] }
}

logs:

<providerName> provider registered error: TypeError: o is not a constructor

and the provider silently fails to load.

Root cause

In ProviderService.initializeFromProvidersArray, the array form is handled by:

const Constructor = this.transformerService.getTransformer(transformer[0]);
if (Constructor) {
  return new (Constructor as TransformerConstructor)(transformer[1]);
}

But getTransformer returns either a class or an already-built instance, depending on how the transformer was registered:

// in registerDefaultTransformersInternal()
if ("TransformerName" in e && typeof e.TransformerName === "string") {
  this.registerTransformer(e.TransformerName, e);   // class
} else {
  const t = new e();
  this.registerTransformer(t.name, t);              // instance
}

Built-in transformers without a static TransformerName (Anthropic, Gemini, OpenAI, Deepseek, etc.) are registered as instances, so new instance(options) throws.

The string-only form already handled both cases with a typeof === 'function' check; the array-with-options form did not.

Fix

Check whether the resolved value is a class (function) or an instance:

• Class: instantiate as before.
• Instance: build a fresh instance via its .constructor so the requested options take effect without mutating the shared instance registered globally.

Applied to both transformer.use and model-specific transformer[model].use.

Use case

{
  "transformer": { "use": [["Anthropic", { "UseBearer": true }]] }
}

Now correctly switches the Anthropic transformer to send Authorization: Bearer ... instead of x-api-key, useful for Anthropic-compatible endpoints whose auth scheme differs from Anthropic's official endpoint.