Speed up startup: parallel JS loading + versioned asset caching

loader.js:
- Fetch /api/version first; append ?v=<version> to every script URL
- Load scripts with async=false (fetch in parallel, execute in DOM order)
- 4 sequential batches instead of 17 sequential awaits:
    utils → settings → [9 feature modules] → init → [4 post-init] → nav
- 17 round-trips → 6 round-trips; 9 and 4 files now download in parallel
- Section HTML keeps ?v=<timestamp> (no-store, always fresh)

server.py:
- Add static_cache_headers middleware:
    /static/js/*?v=...  → Cache-Control: max-age=31536000, immutable
    /static/sections/*  → Cache-Control: no-store
    /static/* (no v=)   → Cache-Control: max-age=3600

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

CHANGELOG.md

@@ -7,6 +7,22 @@ Follows [Keep a Changelog](https://keepachangelog.com/en/1.0.0/) · versioned wi
 
 ## [Unreleased]
 
+### Performance
+
+- **Parallel JS module loading** — `loader.js` previously loaded all 16
+  modules sequentially (17 round-trips). Restructured into 4 ordered batches
+  with `async=false` so files are fetched in parallel but execute in the
+  correct dependency order:
+  `utils` → `settings` → *(9 feature modules in parallel)* → `init` →
+  *(4 post-init modules in parallel)* → `nav`
+  Round-trips reduced from 17 to 6; 9 files now download simultaneously.
+- **Version-based JS/CSS cache busting** — `loader.js` fetches
+  `/api/version` first and appends `?v=<version>` to every script URL.
+  A new `Cache-Control: public, max-age=31536000, immutable` middleware in
+  `server.py` lets the browser cache versioned assets for a full year.
+  Bumping the version (via `scripts/release.py`) invalidates the cache.
+  Section HTML keeps `?v=<timestamp>` (no-store) so it is always fresh.
+
 ### Changed
 
 - **Config and logs are now bind-mounted local folders** — replaced the

server.py

@@ -6,7 +6,8 @@ import os
 from logging.handlers import RotatingFileHandler
 from pathlib import Path
 
-from fastapi import FastAPI
+from fastapi import FastAPI, Request
+from fastapi.responses import Response
 from fastapi.staticfiles import StaticFiles
 
 from core.constants import STATIC_DIR, _BufferHandler
@@ -44,6 +45,24 @@ try:
 except Exception as _log_err:
     logger.warning("Could not set up file logging at %s: %s", _LOG_DIR, _log_err)
 
+# ── Static-asset caching middleware ──────────────────────────────────────────
+# JS and CSS are served with ?v=<version> by loader.js — safe to cache for 1 year.
+# Section HTML uses ?v=<timestamp> (always fresh) so no long-term cache there.
+
+@app.middleware("http")
+async def static_cache_headers(request: Request, call_next):
+    response: Response = await call_next(request)
+    path = request.url.path
+    has_version = bool(request.query_params.get("v"))
+    if has_version and (path.startswith("/static/js/") or path.endswith(".css")):
+        response.headers["Cache-Control"] = "public, max-age=31536000, immutable"
+    elif path.startswith("/static/sections/"):
+        response.headers["Cache-Control"] = "no-store"
+    elif path.startswith("/static/") and not has_version:
+        response.headers["Cache-Control"] = "public, max-age=3600"
+    return response
+
+
 # ── Routers ───────────────────────────────────────────────────────────────────
 
 app.include_router(admin.router)

static/loader.js

@@ -1,58 +1,96 @@
 (async function () {
   'use strict';
 
-  const SECTIONS = ['s-voices', 's-clone', 's-design', 's-studio', 's-tryout', 's-performance', 's-routing', 's-connect', 's-settings', 's-llms', 's-conversation'];
+  const SECTIONS = [
+    's-voices', 's-clone', 's-design', 's-studio', 's-tryout',
+    's-performance', 's-routing', 's-connect', 's-settings',
+    's-llms', 's-conversation',
+  ];
 
-  function loadScript(src) {
+  // ── Fetch app version once for JS cache-busting ──────────────────────────
+  // JS files are served with ?v=<version> so the browser can cache them
+  // aggressively.  Sections use Date.now() to always get fresh HTML.
+  var _appVersion = 'dev';
+  try {
+    var _vr = await fetch('/api/version');
+    var _vd = await _vr.json();
+    _appVersion = _vd.version || _appVersion;
+  } catch (_) {}
+
+  // ── 1. Fetch all section HTML partials in parallel ────────────────────────
+  var _ts = Date.now(); // sections always fresh during a session
+  await Promise.all(SECTIONS.map(async function (id) {
+    try {
+      var res = await fetch('/static/sections/' + id + '.html?v=' + _ts);
+      if (!res.ok) throw new Error(res.status + ' ' + res.statusText);
+      var el = document.getElementById(id);
+      if (el) el.innerHTML = await res.text();
+    } catch (e) {
+      console.error('[loader] section', id, 'failed:', e.message);
+      var el = document.getElementById(id);
+      if (el) el.innerHTML =
+        '<p style="color:var(--red);padding:24px">Failed to load section <b>' +
+        id + '</b>: ' + e.message + '</p>';
+    }
+  }));
+
+  // ── 2. Load JS in parallel batches ────────────────────────────────────────
+  // Scripts with async=false are FETCHED in parallel but EXECUTED in DOM
+  // insertion order — safe for modules that share a global scope.
+  //
+  // Batch order:
+  //   A) utils.js          — defines $, toast, escHtml; needed by everything
+  //   B) settings.js       — declares _appSettings; needed before features read it
+  //   C) Feature modules   — parallel fetch + ordered execute
+  //   D) init.js           — calls loadSettings() + initBenchmarkSampleControls()
+  //   E) Post-init modules — parallel fetch + ordered execute
+  //   F) nav.js            — navigation overrides; must be last
+
+  function _load(src) {
     return new Promise(function (resolve, reject) {
       var s = document.createElement('script');
-      s.src = src;
+      s.src = src + '?v=' + _appVersion;
+      s.async = false;   // fetch in parallel, execute in DOM order
       s.onload  = resolve;
       s.onerror = function () { reject(new Error('Failed to load ' + src)); };
       document.body.appendChild(s);
     });
   }
 
-  // 1. Fetch all section partials in parallel and inject into their shells.
-  //    ?v= busts the browser cache so updated HTML is always used.
-  var _v = Date.now();
-  await Promise.all(SECTIONS.map(async function (id) {
-    try {
-      var res = await fetch('/static/sections/' + id + '.html?v=' + _v);
-      if (!res.ok) throw new Error(res.status + ' ' + res.statusText);
-      var html = await res.text();
-      var el = document.getElementById(id);
-      if (el) el.innerHTML = html;
-    } catch (e) {
-      console.error('[loader] section', id, 'failed:', e.message);
-      var el = document.getElementById(id);
-      if (el) el.innerHTML = '<p style="color:var(--red);padding:24px">Failed to load section <b>' + id + '</b>: ' + e.message + '</p>';
+  function _loadBatch(srcs) {
+    // Append all <script async=false> at once → browser fetches all in parallel
+    // and executes them in the order they were appended.
+    return Promise.all(srcs.map(_load));
   }
-  }));
 
-  // 2. Load main application logic (runs init immediately on parse — sections must exist first)
-  const JS_MODULES = [
-    '/static/js/utils.js',
+  // A — foundation (sequential: each must finish before the next batch starts)
+  await _load('/static/js/utils.js');
+  await _load('/static/js/settings.js');
+
+  // C — feature modules (9 files fetched in parallel, executed in order)
+  await _loadBatch([
     '/static/js/voice-inspector.js',
     '/static/js/voice-sources.js',
     '/static/js/integrations.js',
     '/static/js/routing.js',
-    '/static/js/settings.js',
     '/static/js/voice-clone.js',
     '/static/js/voice-library.js',
     '/static/js/tts-preview.js',
     '/static/js/benchmark.js',
     '/static/js/stt.js',
-    '/static/js/init.js',
+  ]);
+
+  // D — init (needs everything above to be defined)
+  await _load('/static/js/init.js');
+
+  // E — post-init modules (4 files fetched in parallel, executed in order)
+  await _loadBatch([
     '/static/js/engines.js',
     '/static/js/ai-backends.js',
     '/static/js/generation.js',
     '/static/js/conversation.js',
-  ];
-  for (const src of JS_MODULES) {
-    await loadScript(src);
-  }
+  ]);
 
-  // 3. Apply scroll-based navigation overrides (must run after app.js defines switchTab etc.)
-  await loadScript('/static/nav.js');
+  // F — navigation
+  await _load('/static/nav.js');
 })();