fix(ci): copy app/ to modules/lib/arbiter/ so Zephyr CMake finds the module

west skips cloning the manifest project to its declared module path; the
cp ensures modules/lib/arbiter/ exists with the correct content and is
captured in the west workspace cache for subsequent runs.

Drop ZEPHYR_EXTRA_MODULES which was not resolving the missing Kconfig issue.

Co-Authored-By: Oz <oz-agent@warp.dev>

Author: tbitcs

.github/workflows/ci.yml

@@ -61,9 +61,6 @@ jobs:
     env:
       # native_sim uses host GCC; skip cross-compiler toolchain lookup.
       ZEPHYR_TOOLCHAIN_VARIANT: host
-      # app/ is the arbiter module checkout; register it as an extra module
-      # so Zephyr CMake loads its Kconfig and cmake files.
-      ZEPHYR_EXTRA_MODULES: ${{ github.workspace }}/app
     steps:
       - uses: actions/checkout@v4
         with:
@@ -106,6 +103,18 @@ jobs:
         if: steps.cache-west.outputs.cache-hit != 'true'
         run: west update --narrow -o=--depth=1
 
+      # west treats the manifest project as already-present at app/ and will
+      # NOT clone it to modules/lib/arbiter/ (its declared path).  Copy it
+      # there so Zephyr CMake can discover the module's Kconfig + cmake files.
+      # This runs only on cache miss so the copy ends up in the restored cache.
+      - name: Place arbiter at canonical module path
+        if: steps.cache-west.outputs.cache-hit != 'true'
+        run: |
+          mkdir -p modules/lib
+          if [ ! -d modules/lib/arbiter ]; then
+            cp -rp app modules/lib/arbiter
+          fi
+
       - name: Install Zephyr Python requirements
         run: pip install -r zephyr/scripts/requirements.txt