feedBack-desktop/scripts/VST_TRACE_README.md

VST trace — runtime-gated diagnostic logging

src/audio/VSTTrace.h defines a VST_TRACE(...) macro the addon, the VST host code, and the sandbox subprocess all use to emit lines into %TEMP%\slopsmith-vst-trace-<pid>.log (Linux/macOS: /tmp/slopsmith-vst-trace-<pid>.log) and stderr. The filename is per-PID so concurrent runs (e.g. addon spawning a sandbox subprocess) each get their own log without interleaving. It's compiled into every build but no-ops at runtime unless the SLOPSMITH_SANDBOX_DEBUG environment variable is set to a non-empty value other than "0".

The first call caches the env var, so flipping the variable mid-process has no effect — set it before launching the host process (node ..., electron ..., or the sandbox subprocess via the parent's environment).

What you'll see when it's enabled

• [ctrl] ... — control-channel framing from ControlChannel.cpp (ConnectNamedPipe, readFrame got N bytes, event: ready, error codes).
• Sandbox subprocess startup steps from slopsmith-vst-host.exe: args ok, audio shm opened, control pipe connected, plugin loaded: <name>, sending ready event.
• LoadVST: path='...', SubprocessHandle.start: spawned pid=N, the full CreateProcess command line.
• VSTHost.loadPlugin / VST3ComponentHolder.initialise host-callback traces from the JUCE VST3 host context (in-process load path only).

The sandbox host also opens a per-PID file at %TEMP%\slopsmith-vst-host-<pid>.log unconditionally — this is by design and intentionally not gated on SLOPSMITH_SANDBOX_DEBUG. The sandbox subprocess runs hidden (no console window) and can die before the env var has propagated, so an always-on per-PID file is the only reliable way to diagnose "the subprocess died and I have no console" crashes in the field. The file is small (a handful of lines per session), written from a single process, and rotates per PID so they cap naturally.

Turning it on

:: Windows — set before launching node / electron / the desktop app:
set SLOPSMITH_SANDBOX_DEBUG=1
node load-gr6.js

# macOS / Linux:
SLOPSMITH_SANDBOX_DEBUG=1 node load-gr6.js

Reading the log

The <pid> portion is the OS process ID of the writer — find your most recent run via dir %TEMP%\slopsmith-vst-trace-*.log (Windows) or ls -t /tmp/slopsmith-vst-trace-*.log | head (POSIX).

:: Windows — view the most recently modified trace file:
for /f "delims=" %f in ('dir /b /o-d %%TEMP%%\slopsmith-vst-trace-*.log') do @type "%%TEMP%%\%f" & exit /b

# macOS / Linux
cat "$(ls -t /tmp/slopsmith-vst-trace-*.log | head -1)"

Per-PID naming means files accumulate over time. Clean up periodically with del %TEMP%\slopsmith-vst-trace-*.log (Windows) or rm /tmp/slopsmith-vst-trace-*.log (POSIX) when they're no longer needed.