r27: WORKDIR in builder stages (stage split dropped inherited cwd)

docker-images/glm53-jovian-r27/Dockerfile

@@ -85,6 +85,7 @@ COPY fetch-deps.sh /tmp/fetch-deps.sh
 RUN bash /tmp/fetch-deps.sh
 
 FROM deps-fetched AS vllm-builder
+WORKDIR /workspace/vllm
 ARG DEEPGEMM_REF
 ARG VLLM_PRETEND_VERSION
 ARG SOURCE_DATE_EPOCH
@@ -154,6 +155,7 @@ RUN set -eux; \
     git config --global --add safe.directory /workspace/b12x
 
 FROM b12x-clone AS b12x-builder
+WORKDIR /workspace/b12x
 ARG B12X_PRETEND_VERSION
 RUN --mount=type=cache,id=uv-cache,target=/root/.cache/uv \
     SETUPTOOLS_SCM_PRETEND_VERSION_FOR_B12X="${B12X_PRETEND_VERSION}" \
@@ -171,6 +173,7 @@ RUN set -eux; \
     cd /workspace/lmcache; \
     test "$(git rev-parse HEAD^{tree})" = "${LMCACHE_TREE}"; \
     git config --global --add safe.directory /workspace/lmcache
+WORKDIR /workspace/lmcache
 RUN --mount=type=cache,id=uv-cache,target=/root/.cache/uv \
     uv pip install "setuptools>=77.0.3,<81.0.0" setuptools_scm wheel packaging ninja \
     && SETUPTOOLS_SCM_PRETEND_VERSION_FOR_LMCACHE="${LMCACHE_VERSION}" \