feat(audio): ASIO/exclusive — renderer-bus in streamer mix, loopback plumbing, cache clear (#98)

* feat(audio): renderer-bus in streamer mix + whole-app loopback plumbing

Two tester-confirmed gaps under ASIO/exclusive output:

1. Streamer mix carried guitar only when the song rode the renderer bus:
   composeAndPushStreamMix mixed guitar + native backing, never the bus.
   The bus ring is single-consumer, so the consumer step is reworked from
   mixRendererBusInto (drain+add) to pullRendererBus (drain once into a
   fixed scratch); both output callbacks then share the pulled block
   between the device output and the stream submix (rides includeBacking
   — it IS song audio).

2. Previews/UI sounds bypass the per-surface feeder taps entirely and
   leak to the default WASAPI device (audible under ASIO, which doesn't
   silence that endpoint). New plumbing lets the static bundle capture
   ALL app audio: setDisplayMediaRequestHandler answers with this
   window's own frame as audio source (frame-scoped — no other apps'
   audio), plus audio:setPageMuted IPC + preload setPageMuted() as the
   local-silence fallback when suppressLocalAudioPlayback is unsupported.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* feat(diag): engine health metrics on every [asio-diag] line

Tester symptom: all audio dead after stopping a song with tones active.
The snapshot showed routing state but not whether the engine was still
producing. Append volatile fields (outside change-detection): in/out/
backing levels, bus fill, input overflows, output underflows, split-ring
fill — outputLevel≈0 with running=true is the silent-engine signature.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* fix(main): clear Chromium HTTP cache before first load

Testers hop between portable builds sharing one userData dir; an older
build's server sent no Cache-Control, so its cached /static/app.js
outlived it and silently replaced the new build's renderer code (the
fix14 'watcher never installed' log). One cheap clearCache() per launch
makes stale-bundle states impossible even against old-server caches.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

src/main/main.ts

@@ -56,7 +56,7 @@ if (process.platform !== 'linux') {
 }
 // ──────────────────────────────────────────────────────────────────────────
 
-import { app, BrowserWindow, ipcMain, dialog, shell, session, crashReporter, powerSaveBlocker, systemPreferences, screen } from 'electron';
+import { app, BrowserWindow, ipcMain, dialog, shell, session, crashReporter, powerSaveBlocker, systemPreferences, desktopCapturer, screen } from 'electron';
 import * as path from 'path';
 import * as fs from 'fs';
 import { execFileSync } from 'child_process';
@@ -500,10 +500,49 @@ function createWindow(port: number): void {
         console.log(`${prefix} ${message}`);
     });
 
+    // Whole-app audio capture for exclusive-style outputs (ASIO / WASAPI
+    // exclusive). The renderer-bus feeder in the static bundle calls
+    // getDisplayMedia({audio, video}) to capture EVERY sound the app makes
+    // (song, previews, UI) and push it into the engine's renderer bus —
+    // per-surface taps can't cover plugin-private AudioContexts. Answer the
+    // request with this window's own frame as the audio source (frame-scoped:
+    // other applications' audio is NOT captured — a system 'loopback' would
+    // leak Discord/etc. into the performance mix) and any screen as the
+    // required-but-unused video track (the feeder stops it immediately).
+    session.defaultSession.setDisplayMediaRequestHandler((_request, callback) => {
+        desktopCapturer.getSources({ types: ['screen'] }).then((sources) => {
+            if (!mainWindow || sources.length === 0) { callback({}); return; }
+            callback({ video: sources[0], audio: mainWindow.webContents.mainFrame });
+        }).catch(() => callback({}));
+    });
+
+    // Local-mute companion for the capture above: when the feeder engages
+    // loopback it must stop the page's audio from ALSO reaching the default
+    // WASAPI device. Preferred path is the suppressLocalAudioPlayback track
+    // constraint; this IPC is the fallback when the constraint is
+    // unsupported. Chromium's capture pipeline taps frame audio before the
+    // output mute, so a muted page still feeds the captured stream.
+    ipcMain.handle('audio:setPageMuted', (_event, muted: unknown) => {
+        if (!mainWindow) return false;
+        mainWindow.webContents.setAudioMuted(muted === true);
+        return mainWindow.webContents.isAudioMuted();
+    });
+
     const serverUrl = `http://127.0.0.1:${port}`;
 
+    // Clear the Chromium HTTP cache before the first load. The server
+    // historically sent no Cache-Control on /static, so heuristic freshness
+    // let a NEW build's window run the PREVIOUS build's app.js from disk
+    // cache (2026-07-11 ASIO investigation: the whole exclusive-reroute chain
+    // silently missing). The server now sends no-cache, but testers hop
+    // between portable builds sharing one userData dir — one cheap clear per
+    // launch makes stale-bundle states impossible regardless of what an
+    // older build's server cached.
+    const clearCachePromise = mainWindow.webContents.session.clearCache()
+        .catch((e) => console.warn(`[main] clearCache failed (continuing): ${e.message}`));
+
     // Small delay to ensure server is fully accepting connections, then load
-    setTimeout(() => mainWindow?.loadURL(serverUrl), 500);
+    setTimeout(() => { void clearCachePromise.then(() => mainWindow?.loadURL(serverUrl)); }, 500);
 
     // Retry loading if the server wasn't reachable yet. Previously this
     // retried just once, which left the window stuck on Chromium's