step E fix (Option 3): bake android24→26 clang shim into image

Incremental Step E (commit 4250f1b) proved that merely compiling the
Oboe C++ bridge into libwzp_desktop_lib.so — with NO Rust-side FFI
bindings, no function calls — resurrects the __init_tcb+4 / pthread_
create SIGSEGV at WryActivity.onCreate. Bisection:

  build #17 (baseline)   ✓
  build #18 (Step A, hello.c)              ✓
  build #19 (Step B, wzp-client dep)       ✓
  build #21 (Step C, engine mod compiled)  ✓
  build #22 (Step D, getauxval_fix.c)      ✓
  build #23 (Step E, Oboe C++ compiled)    ✗ — __init_tcb+4 crash

Root cause: tauri-cli hard-codes `aarch64-linux-android24-clang` as the
Rust linker. Without any C++ code in the .so, libstd's pthread_create
reference gets resolved against the dynamic libc.so. The moment we add
a C++ static library that links against libc++_shared, the link-time
resolution pulls in the API-24 libc.a static pthread_create stub — and
Rust's libstd then also calls that stub instead of libc.so's real one.
The stub calls __init_tcb which SIGSEGVs because bionic's TCB state
only exists for static-libc main executables, not .so's loaded via
dlopen. API-26 NDK has proper dynamic bindings that resolve correctly.

Option 3 fix: at image build time, replace every NDK
aarch64-linux-android24-clang (and armv7/x86_64/i686, clang/clang++)
binary with a one-line shell script that exec()s the corresponding
android26-clang. Since tauri-cli invokes the linker via absolute path,
PATH and env var overrides fail — but replacing the binary on disk
inside the image is guaranteed to take effect. The legacy wzp-android
crate doesn't need this because cargo-ndk respects .cargo/config.toml
where a crate-level linker override is set.

Only changing the Dockerfile here. Next: rebuild the image no-cache,
retry Step E, and if the baseline holds, proceed to Steps F/G.

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

scripts/Dockerfile.android-builder

@@ -74,6 +74,30 @@ RUN yes | $ANDROID_HOME/cmdline-tools/latest/bin/sdkmanager --licenses > /dev/nu
         "platform-tools" \
         2>&1 | grep -v '^\[' > /dev/null
 
+# Work around the API-24 libc.a stub in the NDK. Any C++ static lib we
+# link into libwzp_desktop_lib.so (e.g. the Oboe audio bridge) pulls in
+# bionic's static pthread_create from API-24 libc.a via libc++_shared,
+# and that pthread_create crashes at __init_tcb+4 when called from a
+# .so loaded via dlopen (the static stub expects libc init state that
+# only exists for main executables). API-26 has the proper runtime
+# bindings. Tauri-cli hard-codes aarch64-linux-android24-clang as the
+# linker and ignores .cargo/config.toml overrides, so the only sure
+# fix is to replace the NDK's ${abi}24-clang binary itself with a
+# shim that exec()s the ${abi}26-clang equivalent. Applies to all four
+# ABIs × {clang, clang++}. The legacy wzp-android crate works without
+# this because cargo-ndk honours a crate-level linker override; the
+# shim is the minimal targeted fix for the cargo-tauri build path.
+# Added as Option 3 for the incremental Step E regression (commit 4250f1b).
+RUN set -eux; \
+    BIN=$ANDROID_NDK_HOME/toolchains/llvm/prebuilt/linux-x86_64/bin; \
+    for abi in aarch64-linux-android armv7a-linux-androideabi i686-linux-android x86_64-linux-android; do \
+        for suffix in clang clang++; do \
+            mv "$BIN/${abi}24-${suffix}" "$BIN/${abi}24-${suffix}.orig"; \
+            printf '#!/bin/sh\nexec "%s/%s26-%s" "$@"\n' "$BIN" "$abi" "$suffix" > "$BIN/${abi}24-${suffix}"; \
+            chmod +x "$BIN/${abi}24-${suffix}"; \
+        done; \
+    done
+
 # Make SDK world-readable so builder user can access it
 RUN chmod -R a+rX $ANDROID_HOME