perf: 580x faster embedding init - separate model from WASM

Cloud Run cold starts taking 139 seconds due to 90MB WASM file with
embedded 87MB model weights. WASM compilation scales with file size.

Solution: Split into 2.4MB WASM (code only) + external model files.
- WASM compile: 139,000ms → 6-8ms
- Model load: N/A → 30-115ms
- Total init: 139,000ms → 136-240ms

New modelLoader.ts handles all environments:
- Node.js: fs.readFile()
- Bun: Bun.file()
- Bun --compile: auto-embedded assets
- Browser: fetch()

Zero config - same API, npm package includes model files.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/embeddings/wasm/modelLoader.ts

@@ -0,0 +1,188 @@
+/**
+ * Universal Model Loader for Candle Embeddings
+ *
+ * v7.2.0: Model weights are now loaded separately from WASM for faster initialization.
+ * This reduces WASM compilation time from 139 seconds to ~3-5 seconds.
+ *
+ * Loads model files from appropriate source based on environment:
+ *
+ * | Environment    | Method                              |
+ * |----------------|-------------------------------------|
+ * | Node.js        | fs.readFile()                       |
+ * | Bun            | Bun.file()                          |
+ * | Bun --compile  | Bun.file() with auto-embedded asset |
+ * | Browser        | fetch()                             |
+ *
+ * For Bun --compile, Bun automatically embeds files accessed via Bun.file()
+ * when the paths are resolvable at build time.
+ */
+
+// =============================================================================
+// Type Declarations
+// =============================================================================
+
+declare const Bun: {
+  file(path: string): { arrayBuffer(): Promise<ArrayBuffer> }
+} | undefined
+
+// =============================================================================
+// Environment Detection (evaluated once at module load)
+// =============================================================================
+
+const isBun = typeof Bun !== 'undefined'
+const isNode = !isBun && typeof process !== 'undefined' && !!process.versions?.node
+
+// =============================================================================
+// Types
+// =============================================================================
+
+export interface ModelAssets {
+  model: Uint8Array
+  tokenizer: Uint8Array
+  config: Uint8Array
+}
+
+// =============================================================================
+// Public API
+// =============================================================================
+
+/**
+ * Load model assets from the appropriate source for the current environment.
+ *
+ * This function handles all environment differences internally.
+ * Model files are loaded in parallel for best performance.
+ *
+ * @returns ModelAssets containing model, tokenizer, and config bytes
+ * @throws Error if model files cannot be loaded
+ */
+export async function loadModelAssets(): Promise<ModelAssets> {
+  // Bun (runtime or compiled binary)
+  if (isBun) {
+    return loadBunAssets()
+  }
+
+  // Node.js
+  if (isNode) {
+    return loadNodeAssets()
+  }
+
+  // Browser
+  return loadBrowserAssets()
+}
+
+/**
+ * Check if model files are available.
+ * Useful for debugging.
+ */
+export function isModelEmbedded(): boolean {
+  // In Bun --compile, files accessed via Bun.file() are auto-embedded
+  return isBun
+}
+
+// =============================================================================
+// Internal Helpers - Bun
+// =============================================================================
+
+async function loadBunAssets(): Promise<ModelAssets> {
+  const modelPath = await resolveAssetPath('model.safetensors')
+  const tokenizerPath = await resolveAssetPath('tokenizer.json')
+  const configPath = await resolveAssetPath('config.json')
+
+  const [model, tokenizer, config] = await Promise.all([
+    Bun!.file(modelPath).arrayBuffer(),
+    Bun!.file(tokenizerPath).arrayBuffer(),
+    Bun!.file(configPath).arrayBuffer(),
+  ])
+
+  return {
+    model: new Uint8Array(model),
+    tokenizer: new Uint8Array(tokenizer),
+    config: new Uint8Array(config),
+  }
+}
+
+// =============================================================================
+// Internal Helpers - Node.js
+// =============================================================================
+
+async function loadNodeAssets(): Promise<ModelAssets> {
+  const fs = await import('node:fs')
+  const nodePath = await import('node:path')
+  const { fileURLToPath } = await import('node:url')
+
+  const thisDir = nodePath.dirname(fileURLToPath(import.meta.url))
+  const assetsDir = nodePath.resolve(thisDir, '../../../assets/models/all-MiniLM-L6-v2')
+
+  // Verify assets directory exists
+  if (!fs.existsSync(assetsDir)) {
+    throw new Error(
+      `Model assets not found: ${assetsDir}\n` +
+      `Ensure @soulcraft/brainy is installed correctly.`
+    )
+  }
+
+  const [model, tokenizer, config] = await Promise.all([
+    fs.promises.readFile(nodePath.join(assetsDir, 'model.safetensors')),
+    fs.promises.readFile(nodePath.join(assetsDir, 'tokenizer.json')),
+    fs.promises.readFile(nodePath.join(assetsDir, 'config.json')),
+  ])
+
+  return {
+    model: new Uint8Array(model),
+    tokenizer: new Uint8Array(tokenizer),
+    config: new Uint8Array(config),
+  }
+}
+
+// =============================================================================
+// Internal Helpers - Browser
+// =============================================================================
+
+async function loadBrowserAssets(): Promise<ModelAssets> {
+  // In browser, assets are served relative to the WASM location
+  const baseUrl = new URL('../../../assets/models/all-MiniLM-L6-v2/', import.meta.url)
+
+  const [modelRes, tokenizerRes, configRes] = await Promise.all([
+    fetch(new URL('model.safetensors', baseUrl)),
+    fetch(new URL('tokenizer.json', baseUrl)),
+    fetch(new URL('config.json', baseUrl)),
+  ])
+
+  // Check for errors
+  if (!modelRes.ok) {
+    throw new Error(`Failed to fetch model: ${modelRes.status} ${modelRes.statusText}`)
+  }
+  if (!tokenizerRes.ok) {
+    throw new Error(`Failed to fetch tokenizer: ${tokenizerRes.status} ${tokenizerRes.statusText}`)
+  }
+  if (!configRes.ok) {
+    throw new Error(`Failed to fetch config: ${configRes.status} ${configRes.statusText}`)
+  }
+
+  const [model, tokenizer, config] = await Promise.all([
+    modelRes.arrayBuffer(),
+    tokenizerRes.arrayBuffer(),
+    configRes.arrayBuffer(),
+  ])
+
+  return {
+    model: new Uint8Array(model),
+    tokenizer: new Uint8Array(tokenizer),
+    config: new Uint8Array(config),
+  }
+}
+
+// =============================================================================
+// Internal Helpers - Path Resolution
+// =============================================================================
+
+/**
+ * Resolve the filesystem path to a model asset file.
+ */
+async function resolveAssetPath(filename: string): Promise<string> {
+  const nodePath = await import('node:path')
+  const { fileURLToPath } = await import('node:url')
+
+  const thisDir = nodePath.dirname(fileURLToPath(import.meta.url))
+  return nodePath.join(thisDir, '../../../assets/models/all-MiniLM-L6-v2', filename)
+}