fix(ci): expose GHA sccache env in shadow-shared-cpu-spike (#950)

Signed-off-by: Jonas Toelke <jtoelke@nvidia.com>

Author: jtoelke2

.github/workflows/shadow-shared-cpu-spike.yml

@@ -43,6 +43,14 @@ jobs:
       - name: Install tools
         run: mise install
 
+      - name: Configure GHA sccache backend
+        # Exposes ACTIONS_CACHE_URL / ACTIONS_RUNTIME_TOKEN to subsequent steps
+        # so sccache (wrapped around rustc via RUSTC_WRAPPER in mise.toml) can
+        # initialize the GHA cache. Without this, sccache fails at startup with
+        # "cache url for ghac not found". The action also installs its own
+        # sccache binary; harmless since mise's sccache remains on PATH.
+        uses: mozilla-actions/sccache-action@7d986dd989559c6ecdb630a3fd2557667be217ad # v0.0.9
+
       - name: Cache Rust target and registry
         uses: Swatinem/rust-cache@779680da715d629ac1d338a641029a2f4372abb5 # v2
         with: