ci: share Linux restore artifacts before builds [CI]

packaging/container/Agent.NativeBuild.Containerfile

@@ -1,24 +1,13 @@
 # Cross-compile Linux binaries on amd64; consumers package these outputs directly.
-ARG NATIVEAOT_BUILDER_IMAGE=localhost/moshiro-dotnet10-nativeaot-aotanywhere:ci
-FROM --platform=linux/amd64 ${NATIVEAOT_BUILDER_IMAGE} AS toolchain
-FROM toolchain AS restore
+ARG NATIVEAOT_RESTORE_IMAGE
+FROM ${NATIVEAOT_RESTORE_IMAGE} AS restore
 WORKDIR /src/backend
-COPY restore/backend/ ./
+COPY source/backend/ ./
+COPY source/packaging/native/msquic/ /src/packaging/native/msquic/
 ARG NODE_RID=linux-musl-arm64
 ARG STATIC_MSQUIC=true
 ENV NUGET_PACKAGES=/root/.nuget/packages
-# Layer hits skip restore. A dependency change still reuses downloaded packages.
-# Seed an empty cache from the baked toolchain instead of downloading SDK/Zig again.
-RUN --mount=type=cache,id=moshiro-nuget,target=/root/.nuget/packages,sharing=locked \
-    --mount=type=bind,from=toolchain,source=/root/.nuget/packages,target=/opt/nuget-seed,ro \
-    cp -a --update=none /opt/nuget-seed/. /root/.nuget/packages/ \
-    && dotnet restore Agent.Native.proj -r "$NODE_RID" -p:PublishAot=true -p:UseAotAnywhere=true -p:SelfContained=true \
-       -p:StaticMsQuic="$STATIC_MSQUIC" -p:StaticExecutable="$STATIC_MSQUIC" \
-       -p:RuntimeFrameworkVersion=10.0.12 -p:InvariantGlobalization=true --artifacts-path /artifacts
-
 FROM restore AS managed
-COPY source/backend/ ./
-COPY source/packaging/native/msquic/ /src/packaging/native/msquic/
 ARG APP_VERSION=0.0.0-dev
 ARG MOSHIRO_TAG=
 ARG MOSHIRO_COMMIT=