qemu-eest: split rustup install into its own step

The previous attempt bundled rustup-init into the install-deps step.
rustup-init's HOME-vs-euid handling left the verify step unable to find
riscv-none-elf-gcc (PATH was not getting the cargo entry, suggesting the
previous step terminated before \$GITHUB_PATH was written).

Split rustup-init into its own step after verify, with CARGO_HOME and
RUSTUP_HOME pinned to /opt so the install does not depend on HOME, and
add --no-modify-path so rustup-init never touches shell rc files.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: somnergy

.github/workflows/qemu-eest-blockchain-rv64.yml

@@ -32,11 +32,6 @@ jobs:
           xpm install @xpack-dev-tools/riscv-none-elf-gcc@latest --global --verbose
           echo 'export PATH=$HOME/.local/xPacks/@xpack-dev-tools/riscv-none-elf-gcc/15.2.0-1.1/.content/bin:$PATH' >> ~/.bashrc
           echo "PATH=$HOME/.local/xPacks/@xpack-dev-tools/riscv-none-elf-gcc/15.2.0-1.1/.content/bin:$PATH" >> $GITHUB_ENV
-          # Rust is needed by `make eest-rlp-build` (z6m_eest_convert converter).
-          # rustup auto-installs the toolchain in prover/rust-toolchain.toml on
-          # the first cargo invocation, so no --default-toolchain pin here.
-          curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y --default-toolchain none --profile minimal
-          echo "$HOME/.cargo/bin" >> $GITHUB_PATH
 
       - name: Verify tool versions
         run: |
@@ -50,6 +45,21 @@ jobs:
           ctest --version
           qemu-system-riscv64 --version
 
+      - name: Install Rust toolchain
+        env:
+          CARGO_HOME: /opt/cargo
+          RUSTUP_HOME: /opt/rustup
+        # cargo is needed by `make eest-rlp-build` (z6m_eest_convert).
+        # CARGO_HOME/RUSTUP_HOME are pinned to /opt so rustup-init does not
+        # trip on the container's HOME vs euid-home mismatch. The toolchain
+        # itself is resolved from prover/rust-toolchain.toml on first call.
+        run: |
+          mkdir -p "$CARGO_HOME" "$RUSTUP_HOME"
+          curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y --no-modify-path --default-toolchain none --profile minimal
+          echo "CARGO_HOME=$CARGO_HOME" >> $GITHUB_ENV
+          echo "RUSTUP_HOME=$RUSTUP_HOME" >> $GITHUB_ENV
+          echo "$CARGO_HOME/bin" >> $GITHUB_PATH
+
       - name: Checkout repository
         uses: actions/checkout@v4
         with:

.github/workflows/qemu-eest-blockchain.yml

@@ -32,11 +32,6 @@ jobs:
           xpm install @xpack-dev-tools/riscv-none-elf-gcc@latest --global --verbose
           echo 'export PATH=$HOME/.local/xPacks/@xpack-dev-tools/riscv-none-elf-gcc/15.2.0-1.1/.content/bin:$PATH' >> ~/.bashrc
           echo "PATH=$HOME/.local/xPacks/@xpack-dev-tools/riscv-none-elf-gcc/15.2.0-1.1/.content/bin:$PATH" >> $GITHUB_ENV
-          # Rust is needed by `make eest-rlp-build` (z6m_eest_convert converter).
-          # rustup auto-installs the toolchain in prover/rust-toolchain.toml on
-          # the first cargo invocation, so no --default-toolchain pin here.
-          curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y --default-toolchain none --profile minimal
-          echo "$HOME/.cargo/bin" >> $GITHUB_PATH
 
       - name: Verify tool versions
         run: |
@@ -50,6 +45,21 @@ jobs:
           ctest --version
           qemu-system-riscv32 --version
 
+      - name: Install Rust toolchain
+        env:
+          CARGO_HOME: /opt/cargo
+          RUSTUP_HOME: /opt/rustup
+        # cargo is needed by `make eest-rlp-build` (z6m_eest_convert).
+        # CARGO_HOME/RUSTUP_HOME are pinned to /opt so rustup-init does not
+        # trip on the container's HOME vs euid-home mismatch. The toolchain
+        # itself is resolved from prover/rust-toolchain.toml on first call.
+        run: |
+          mkdir -p "$CARGO_HOME" "$RUSTUP_HOME"
+          curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y --no-modify-path --default-toolchain none --profile minimal
+          echo "CARGO_HOME=$CARGO_HOME" >> $GITHUB_ENV
+          echo "RUSTUP_HOME=$RUSTUP_HOME" >> $GITHUB_ENV
+          echo "$CARGO_HOME/bin" >> $GITHUB_PATH
+
       - name: Checkout repository
         uses: actions/checkout@v4
         with: