gc_bba_test: fix inverted EXI error checks; builds clean

libogc's EXI functions return '1 on success, <=0 on error', but every call
site tested '== 0'.  A -1 error return therefore read as success, so a failed
EXI_Lock or EXI_Select would fall through and the subsequent transfer would
produce garbage reported as a misleading test failure rather than an EXI
error.  All six call sites now test <= 0.

Also retries EXI_Lock for ~100 ms: it fails outright rather than blocking when
another subsystem holds the channel, and Swiss or a libogc driver may hold it
briefly -- without the retry a transient collision surfaces as a test failure.

Builds clean with devkitPPC 16.1.0 / GCC 16, no warnings: 172 KB .dol.

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

.devcontainer/Dockerfile

@@ -1,3 +1,8 @@
+# devkitPro's official image, used only as a source for the GameCube toolchain
+# (see the devkitPPC section below).  `:latest` tracks devkitPro releases; pin a
+# dated tag (e.g. :20250527) if a toolchain update ever breaks the build.
+FROM devkitpro/devkitppc:latest AS devkitppc
+
 FROM debian:sid-slim
 
 RUN apt-get update && apt-get install -y --no-install-recommends \
@@ -5,6 +10,7 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
     curl \
     git \
     git-lfs \
+    make \
     sudo \
     python3 \
     python3-venv \
@@ -52,21 +58,24 @@ RUN pip install --no-cache-dir pyftdi pyserial
 
 # ── GameCube homebrew toolchain (devkitPPC + libogc) ────────────────────────
 # Needed to build the on-console BBA test app in `gc_bba_test/` into a .dol.
-# devkitPro does NOT publish a .deb on GitHub -- the Debian package only exists
-# in their own apt repo -- so this uses their maintained installer script, which
-# adds the repo, imports the key and installs dkp-pacman.  `gamecube-dev` is a
-# package GROUP (devkitPPC, libogc, libfat, tools incl. elf2dol).
 #
-# NOTE this pulls from apt.devkitpro.org / pkg.devkitpro.org.  Those hosts are
-# blocked (HTTP 403) from inside the running container's network egress, but a
-# host-side `docker build` reaches them fine -- which is why this lives in the
-# Dockerfile rather than being installed at runtime.  Adds roughly 1.5-2 GB.
-RUN curl -fsSL https://apt.devkitpro.org/install-devkitpro-pacman -o /tmp/install-devkitpro-pacman \
- && chmod +x /tmp/install-devkitpro-pacman \
- && yes | /tmp/install-devkitpro-pacman \
- && dkp-pacman -S --noconfirm gamecube-dev \
- && dkp-pacman -Scc --noconfirm \
- && rm -f /tmp/install-devkitpro-pacman
+# Copied out of devkitPro's official `devkitpro/devkitppc` image rather than
+# installed with their `install-devkitpro-pacman` script: apt.devkitpro.org and
+# pkg.devkitpro.org sit behind Cloudflare, which answers curl/wget/scripted
+# fetches with HTTP 403 (browser user-agents get 200) -- from the host's
+# `docker build` too, not just from inside the container.  The Docker image is
+# devkitPro's sanctioned route for CI/containers and needs no network access to
+# their hosts.  The binaries only link against libc, so they run fine on sid.
+#
+# Only the GameCube/PPC parts are copied (~540 MB); devkitARM, wut and the
+# Wii/Wii U portlibs from the source image are skipped.
+COPY --from=devkitppc /opt/devkitpro/devkitPPC         /opt/devkitpro/devkitPPC
+COPY --from=devkitppc /opt/devkitpro/libogc            /opt/devkitpro/libogc
+COPY --from=devkitppc /opt/devkitpro/tools             /opt/devkitpro/tools
+COPY --from=devkitppc /opt/devkitpro/cmake             /opt/devkitpro/cmake
+COPY --from=devkitppc /opt/devkitpro/licenses          /opt/devkitpro/licenses
+COPY --from=devkitppc /opt/devkitpro/portlibs/ppc      /opt/devkitpro/portlibs/ppc
+COPY --from=devkitppc /opt/devkitpro/portlibs/gamecube /opt/devkitpro/portlibs/gamecube
 
 ENV DEVKITPRO=/opt/devkitpro
 ENV DEVKITPPC=/opt/devkitpro/devkitPPC