feat(audio): loopback feeder mode + static no-cache — all app audio under exclusive/ASIO (#877)

* feat(audio): route feedpak full-mix natively under exclusive output

Song playback runs through the renderer, which WASAPI-exclusive (and
ASIO) output silences. Route single-mix feedpaks (stem-less
original_audio packs AND single-stem packs) onto the engine's backing
transport when the output device type is exclusive-style, and migrate
back to HTML5 when it isn't. Extends /api/audio-local-path to resolve
/api/sloppak/.../file/... URLs via the same containment guards as
serve_sloppak_file. Multi-stem packs stay on the WebAudio path
(Phase 2). Includes [feedpak-route] transition-gated diagnostics
logging.

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

* feat(audio): renderer-bus feeder — mix renderer song audio into engine output (Phase 2)

Under exclusive-style output the native backing transport (Phase 1, #824)
carries loose /audio/ songs and feedpak full-mixes, but not the stems
plugin's multi-stem WebAudio graph or tracks JUCE rejected. The feeder taps
the renderer-side master with an AudioWorklet, re-points the owning
AudioContext at a null sink so it keeps rendering without a device, and
pushes ~10 ms chunks over IPC into the desktop engine's renderer bus
(feedBack-desktop#90 follow-up). Inert in the Docker sphere and in shared
mode. Validated by the fix12 tester spike: null-sink rendering works,
clocks hold, no overflow.

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

* feat(diag): --debug ASIO routing diagnostics in static bundle

Gated on window.feedBackDesktop.audio.debugEnabled() (desktop --debug);
inert in the Docker sphere and normal desktop runs.

- [asio-diag] getCurrentDevice= full device object on outputType change
  (catches ASIO drivers reporting a non-'ASIO' type name)
- [asio-diag] renderer-bus: full feeder decision vector, change-gated
  (running/exclusive/stems/juceMode/elementSong/want/mode)
- [asio-diag] setSink: every sink flip with ctx state + rate

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

* feat(audio): loopback feeder mode — all app audio under exclusive/ASIO

Tester-confirmed (2026-07-11 log): song previews and other
plugin-private audio bypass the per-surface feeder taps and leak to the
default WASAPI device under ASIO output. Also confirmed: the element
capture path poisons itself when highway_3d already owns #audio's
one-shot MediaElementSource (InvalidStateError with _elCtx assigned
pre-throw → TypeError every later tick).

- New preferred mode 'loopback': one getDisplayMedia frame-audio capture
  (desktop main answers with the app's own frame) covers song, previews,
  and UI sounds for the whole exclusive session — engages even with no
  song loaded. Local playback silenced via suppressLocalAudioPlayback,
  page-mute IPC fallback otherwise.
- Sticky fallback to the existing stems/element surface modes when
  capture is unavailable (old desktop main, denied, Docker sphere).
- Element capture: assign module state only after the whole chain
  succeeds; close the context on failure — collision now retries clean.
- Failed engage now disables the bus and tears down loopback (no more
  bus-enabled-with-no-producer stranding).
- Tests: 12 (5 new — loopback engage/preference/mute-fallback/sticky
  fallback, collision retry).

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

* feat(audio): loopback feeder mode — all app audio under exclusive/ASIO

Tester-confirmed (2026-07-11 log): song previews and other
plugin-private audio bypass the per-surface feeder taps and leak to the
default WASAPI device under ASIO output. Also confirmed: the element
capture path poisons itself when highway_3d already owns #audio's
one-shot MediaElementSource (InvalidStateError with _elCtx assigned
pre-throw → TypeError every later tick).

- New preferred mode 'loopback': one getDisplayMedia frame-audio capture
  (desktop main answers with the app's own frame) covers song, previews,
  and UI sounds for the whole exclusive session — engages even with no
  song loaded. Local playback silenced via suppressLocalAudioPlayback,
  page-mute IPC fallback otherwise.
- Sticky fallback to the existing stems/element surface modes when
  capture is unavailable (old desktop main, denied, Docker sphere).
- Element capture: assign module state only after the whole chain
  succeeds; close the context on failure — collision now retries clean.
- Failed engage now disables the bus and tears down loopback (no more
  bus-enabled-with-no-producer stranding).
- Tests: 12 (5 new — loopback engage/preference/mute-fallback/sticky
  fallback, collision retry).

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

* fix(audio): close loopback capture context on teardown (release tap worklet)

The loopback context was reused across engages (_lbCtx || new), but teardown
only stopped the stream + deactivated the tap — never closing the context or
detaching the worklet node. Each exclusive<->shared switch orphaned a live
tap worklet on the long-lived context. Use a fresh context per session and
close it on disengage. Adds a test asserting the context is closed on teardown.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* feat(diag): install-time + uncaught-error diagnostics for the reroute chain

2026-07-11 tester log showed the routing watcher and renderer-bus feeder
never installed (zero [feedpak-route]/[renderer-bus] lines) plus an
uncaught SyntaxError with no source location — nothing in the log said
why. New:

- global error/unhandledrejection tap logging message + filename:line:col
  (error events carry the location even for parse errors in other scripts)
- explicit install / NOT-installed lines for watcher and feeder (incl.
  loopback capability probe)
- DOMException detail (name/message/stack head) in the feeder retry warn
  — the console-message forward stringified it to [object DOMException]

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

* fix(static): force conditional revalidation on /static (Cache-Control: no-cache)

Without Cache-Control Chromium's heuristic freshness (10% of file age)
serves /static/app.js from disk cache for hours-to-days without
revalidating. Desktop consequence: a new build's window ran the previous
build's app.js — the 2026-07-11 ASIO investigation traced 'routing
watcher never installed' + a stems module-plugin SyntaxError to exactly
this (stale loader predating scriptType support). no-cache keeps caching
but revalidates via ETag — unchanged files still cost only a 304.

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

* fix(diag): gate install-time + uncaught-error [asio-diag] lines on --debug

The error tap and install lines from the previous diag commit were
unconditional. Now: error/rejection taps check _asioDiagEnabled() at
event time; install lines log deferred once the async debugEnabled()
resolves true. The NOT-installed anomaly lines stay bridge-gated
(window.feedBackDesktop present) instead — a broken bridge can't deliver
the debug flag, they fire at most once, and only in the broken state
they exist to witness. Docker sphere: fully silent.

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

---------

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>
Co-authored-by: Byron Gamatos <xasiklas@gmail.com>

server.py

@@ -2386,7 +2386,25 @@ app.include_router(ws_highway.router)
 
 
 
-app.mount("/static", StaticFiles(directory=str(STATIC_DIR)), name="static")
+class _RevalidatedStaticFiles(StaticFiles):
+    """StaticFiles that forces conditional revalidation on every request.
+
+    Without Cache-Control, Chromium applies heuristic freshness (10% of the
+    file's age since Last-Modified) and serves /static/app.js from its disk
+    cache for hours-to-days without asking the server. In the desktop app that
+    meant a new build's renderer ran the PREVIOUS build's app.js — the
+    2026-07-11 ASIO investigation lost a day to a stale loader that couldn't
+    even load module plugins. `no-cache` does NOT disable caching: the browser
+    keeps the cached copy and revalidates with If-None-Match; unchanged files
+    still cost only a 304."""
+
+    async def get_response(self, path, scope):
+        response = await super().get_response(path, scope)
+        response.headers.setdefault("Cache-Control", "no-cache")
+        return response
+
+
+app.mount("/static", _RevalidatedStaticFiles(directory=str(STATIC_DIR)), name="static")
 
 
 @app.get("/")