fix(sandbox): force PolyChrome DSP plugins out-of-process (in-process WndProc DEP crash) (#34)

* fix(sandbox): force PolyChrome DSP plugins out-of-process (in-process WndProc DEP crash)

A tester crash dump (feedback.exe 0.3.0, Windows) showed an execute-DEP access
violation (0xC0000005) killing the app while McRocklin Suite.vst3 (PolyChrome
DSP) was loaded IN-PROCESS:

  Rax == Rip == McRocklin Suite.vst3 + 0x1D57050   (non-executable module data)
  caller [Rsp] = USER32.dll+0xEF5C
  WndProc(hwnd=0x51CCA, msg=0x1C WM_ACTIVATEAPP, wParam=1, lParam=0x1838)
  crash thread = the addon's background JUCE MessageManager thread (unnamed;
  start frame slopsmith_audio.node), NOT Electron's CrBrowserMain.

PolyChrome creates a top-level window during in-process init on JUCE's
*background* message thread. Its WndProc lands in non-executable memory there, so
when Windows broadcasts WM_ACTIVATEAPP the OS message pump executes it → DEP AV.
The plugin assumes a real host main UI thread (STA/main); the sandbox child
provides exactly that, so routing it out-of-process both isolates the fault and
gives the plugin the environment it needs.

Crucially this crash cannot be caught by the SignalChain in-process fault guard:
it arrives asynchronously via USER32→WndProc with NO host frame on the stack, so
guarding prepareToPlay/processBlock (or even instantiation) never sees it. Under
the current in-process-by-default policy (#24) the only fix is to not host these
plugins in-process. Graphene (same vendor) was already pre-seeded; this extends
the pre-seed to the whole PolyChrome vendor via a path-fragment match so McRocklin
Suite and any other PolyChrome product route to the sandbox too.

- Add kDefaultNeedsSandboxPathFragments (vendor/path match) + the loop in
  shouldSandbox; seed it with "PolyChrome".
- Refresh the stale kDefaultNeedsSandboxFilenames comment (it still claimed
  sandbox-by-default; #24 made the list authoritative again).
- e2e_test: add testShouldSandboxRouting() — pure shouldSandbox assertions
  (PolyChrome→sandbox, clean VST3→in-process, non-VST3→in-process).

Verified: audio addon builds clean; sandbox_e2e_test green (16/16, routing
assertions included).

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

* review: tighten PolyChrome match + dedupe path + harden routing test

Local high-effort review of the pre-seed fix surfaced four items; addressed:

- False-positive risk (no in-process fallback exists here — loadVstSandboxAware
  hard-fails a force-sandboxed load that can't spawn the child): narrow the
  fragment from the bare brand word "PolyChrome" to the vendor install folder
  "PolyChrome DSP", so an unrelated path (e.g. a username "polychrome") no
  longer forces the sandbox. Still matches McRocklin Suite + Graphene, which
  ship under Common Files/VST3/PolyChrome DSP/.
- Dedupe: getFullPathName() was computed twice (blocklist `canonical` +
  vendor `fullPath`); hoist one `fullPath` above the mutex block and reuse it.
- Test isolation: assert McRocklin Suite (NOT in the filename pre-seed) on both
  Windows- and POSIX-style paths so the case can only pass via the new vendor
  match; drop the redundant Graphene-in-folder line (Graphene already routes via
  the filename list).
- Test specificity + exit-code masking: add a negative proving a bare
  "polychrome" path is NOT sandboxed (guards the tightening), and surface
  routing CHECK failures on the no-args path (return 1, not the usage code 2)
  so a regression isn't masked on a manual/argless run.

Addon builds clean; sandbox_e2e_test 17/17 green (routing included).

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

---------

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

tests/sandbox/e2e/e2e_test.cpp

@@ -31,9 +31,50 @@ static bool allClose(const juce::AudioBuffer<float>& b, float v)
     return true;
 }
 
+// Pure routing checks for shouldSandbox() — no spawn / fixture needed. Guards
+// the pre-seed policy: under in-process-by-default, a PolyChrome plugin (whose
+// in-process WndProc DEP-faults via the OS message pump — uncatchable by the
+// SignalChain guard) MUST be forced to the out-of-process sandbox, while an
+// ordinary scanned-clean VST3 stays in-process. See dmp a06f48e1 / McRocklin.
+static void testShouldSandboxRouting()
+{
+    std::printf("--- shouldSandbox routing ---\n");
+    auto desc = [](const char* p)
+    {
+        juce::PluginDescription d;
+        d.fileOrIdentifier = juce::String::fromUTF8(p);
+        return d;
+    };
+    // PolyChrome DSP vendor folder → sandbox. McRocklin Suite is NOT in the
+    // filename pre-seed, so these can only pass via the new vendor/path match —
+    // they directly guard the fix on both Windows- and POSIX-style paths.
+    CHECK(shouldSandbox(desc("C:\\Program Files\\Common Files\\VST3\\PolyChrome DSP\\McRocklin Suite.vst3")));
+    CHECK(shouldSandbox(desc("/Library/Audio/Plug-Ins/VST3/PolyChrome DSP/McRocklin Suite.vst3")));
+    // Filename pre-seed still independently routes Graphene by name.
+    CHECK(shouldSandbox(desc("/plugins/Graphene.vst3")));
+    // Ordinary scanned-clean VST3 stays in-process.
+    CHECK(! shouldSandbox(desc("/Library/Audio/Plug-Ins/VST3/SomeCleanAmp.vst3")));
+    // Specificity: the fragment is the vendor FOLDER, not a bare brand word — a
+    // clean plugin under a path that merely contains 'polychrome' (e.g. a
+    // username) must NOT be force-sandboxed (no in-process fallback exists, so a
+    // false positive could hard-fail the load).
+    CHECK(! shouldSandbox(desc("/Users/polychrome/VST3/SomeCleanAmp.vst3")));
+    // Non-VST3 (NAM/IR) always in-process.
+    CHECK(! shouldSandbox(desc("/models/AwesomeAmp.nam")));
+}
+
 int main(int argc, char** argv)
 {
-    if (argc < 3) { std::fprintf(stderr, "usage: e2e_test <vst-host> <plugin.vst3>\n"); return 2; }
+    testShouldSandboxRouting();
+
+    // Surface routing failures even on the no-args path: the pure routing checks
+    // above need no fixture, so a regression must not be masked by the usage
+    // sentinel (return 1 if a routing CHECK failed, else the usage code 2).
+    if (argc < 3)
+    {
+        std::fprintf(stderr, "usage: e2e_test <vst-host> <plugin.vst3>\n");
+        return g_fail == 0 ? 2 : 1;
+    }
 
     SandboxedProcessor::SpawnConfig cfg;
     cfg.pluginPath     = juce::String::fromUTF8(argv[2]);