Vectors WebLLM (#3631)

* Add WebLLM support for vectorization

* Load models when WebLLM extension installed

* Consistency updated

* Move checkWebLlm to initEngine

* Refactor vector request handling to use getAdditionalArgs

* Add error handling for unsupported WebLLM extension

* Add prefix to error causes

public/scripts/extensions/vectors/webllm.js

@@ -0,0 +1,64 @@
+export class WebLlmVectorProvider {
+    /** @type {object?} WebLLM engine */
+    #engine = null;
+
+    constructor() {
+        this.#engine = null;
+    }
+
+    /**
+     * Check if WebLLM is available and up-to-date
+     * @throws {Error} If WebLLM is not available or not up-to-date
+     */
+    #checkWebLlm() {
+        if (!Object.hasOwn(SillyTavern, 'llm')) {
+            throw new Error('WebLLM is not available', { cause: 'webllm-not-available' });
+        }
+
+        if (typeof SillyTavern.llm.generateEmbedding !== 'function') {
+            throw new Error('WebLLM is not updated', { cause: 'webllm-not-updated' });
+        }
+    }
+
+    /**
+     * Initialize the engine with a model.
+     * @param {string} modelId Model ID to initialize the engine with
+     * @returns {Promise<void>} Promise that resolves when the engine is initialized
+     */
+    #initEngine(modelId) {
+        this.#checkWebLlm();
+        if (!this.#engine) {
+            this.#engine = SillyTavern.llm.getEngine();
+        }
+
+        return this.#engine.loadModel(modelId);
+    }
+
+    /**
+     * Get available models.
+     * @returns {{id:string, toString: function(): string}[]} Array of available models
+     */
+    getModels() {
+        this.#checkWebLlm();
+        return SillyTavern.llm.getEmbeddingModels();
+    }
+
+    /**
+     * Generate embeddings for a list of texts.
+     * @param {string[]} texts Array of texts to generate embeddings for
+     * @param {string} modelId Model to use for generating embeddings
+     * @returns {Promise<number[][]>} Array of embeddings for each text
+     */
+    async embedTexts(texts, modelId) {
+        await this.#initEngine(modelId);
+        return this.#engine.generateEmbedding(texts);
+    }
+
+    /**
+     * Loads a model into the engine.
+     * @param {string} modelId Model ID to load
+     */
+    async loadModel(modelId) {
+        await this.#initEngine(modelId);
+    }
+}