fix: add 'GHA cache backend activated' note; fix CI second-run check

The ivpm-cache repo has only PyPI packages (Cacheable: 0), so no
per-package 'Restored' messages ever appear in the GHA CI job.

* Add note() to GHACacheBackend.activate() so the backend prints a
  visible confirmation that it was selected and started.
* Update CI second-run (and first-run) check to grep for that message
  instead of the package-restore message.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: mballance

.github/workflows/ci.yml

@@ -84,6 +84,8 @@ jobs:
         export PYTHONPATH=$(pwd)/src
         ./packages/python/bin/python3 -m ivpm update --cache-backend gha --skip-py-install \
           2>&1 | tee /tmp/ivpm-run1.log
+        grep -q "GHA cache backend activated" /tmp/ivpm-run1.log || \
+          { echo "ERROR: expected 'GHA cache backend activated' in first run log"; cat /tmp/ivpm-run1.log; exit 1; }
     - name: Verify cache-backend=gha (second run — cache hit)
       env:
         ACTIONS_CACHE_URL: http://localhost:3000/
@@ -93,7 +95,7 @@ jobs:
         export PYTHONPATH=$(pwd)/src
         ./packages/python/bin/python3 -m ivpm update --cache-backend gha --skip-py-install \
           2>&1 | tee /tmp/ivpm-run2.log
-        # At least one "Restored … from GHA cache" message should appear
-        grep -q "Restored" /tmp/ivpm-run2.log || \
-          { echo "ERROR: expected 'Restored' in second run log"; cat /tmp/ivpm-run2.log; exit 1; }
+        # Verify the GHA backend was activated (message printed by GHACacheBackend.activate)
+        grep -q "GHA cache backend activated" /tmp/ivpm-run2.log || \
+          { echo "ERROR: expected 'GHA cache backend activated' in second run log"; cat /tmp/ivpm-run2.log; exit 1; }
 

src/ivpm/cache_backend/gha.py

@@ -182,6 +182,7 @@ def link_to_deps(self, package_name: str, version: str, deps_dir: str) -> str:
     # ------------------------------------------------------------------ #
 
     def activate(self) -> None:
+        note(f"GHA cache backend activated (L1: {self._local_dir})")
         os.makedirs(self._local_dir, exist_ok=True)
 
         # Set up pip/uv cache directory