step E.1: absolute minimum C++ file (no STL, no includes)

Last bisection step. cpp/cpp_smoke.cpp reduced to a single extern 'C'
function that returns 42. No #include, no std::atomic, no std::mutex,
no std::thread. Only C++ things remaining are:
  - cc::Build::new().cpp(true) in build.rs (C++ mode compile)
  - cpp_link_stdlib('c++_shared') emitting -lc++_shared

If this still crashes with the same __init_tcb+4 / pthread_create
stack, we've conclusively proven the trigger is NOT any C++ code
that ends up in the final .so (everything gets dead-stripped
anyway because Rust never references wzp_cpp_hello). The trigger
must be either:
  a) cargo:rustc-link-lib=c++_shared (adds NEEDED entry for
     libc++_shared.so in the .so's dynamic table, causing the
     dynamic linker to load libc++_shared.so at dlopen() time
     alongside our .so), or
  b) Some interaction between cpp(true) mode and the rest of the
     build pipeline (toolchain flags, symbol visibility, etc.)

After this build we stop and write an incident report for the
WarzonePhone Tauri Android rewrite bisection so far.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

desktop/src-tauri/cpp/cpp_smoke.cpp

@@ -1,19 +1,14 @@
-// cpp_smoke.cpp — Step E.2 minimal stub: std::atomic only, no thread/mutex.
+// cpp_smoke.cpp — Step E.1: the absolute minimum C++ file.
+// No #include, no STL, no atomics, no thread, no mutex. Just one function.
+// Still compiled as .cpp(true) with cpp_link_stdlib("c++_shared"), so the
+// only delta vs the non-crashing baseline is:
+//   1. cc::Build using cpp(true) (vs plain C in hello.c)
+//   2. cargo:rustc-link-lib=c++_shared emitted by cc-rs (adds NEEDED
+//      entry for libc++_shared.so in the final .so)
 //
-// Linked via cpp_link_stdlib("c++_shared") so the resulting .so still carries
-// a NEEDED entry for libc++_shared.so exactly like the Oboe build would.
-//
-// Same extern "C" export as E.4 so the linker CAN pull the symbol in if it
-// chooses to, but since Rust never calls it, it'll typically be dead-stripped.
-// The diagnostic value is in the build.rs link directives this compile
-// produces, not in the file's actual code being linked.
+// If this crashes, we've conclusively proven the trigger is one of those
+// two things — not any C++ code behavior.
 
-#include <atomic>
-
-namespace {
-    std::atomic<int> g_counter{0};
-}
-
-extern "C" int wzp_cpp_smoke(void) {
-    return g_counter.fetch_add(1);
+extern "C" int wzp_cpp_hello(void) {
+    return 42;
 }