ci: add debugging to investigate cache behavior

Author: xdustinface

.github/workflows/build-and-test.yml

@@ -24,12 +24,30 @@ jobs:
       - uses: dtolnay/rust-toolchain@stable
       - uses: Swatinem/rust-cache@v2
         with:
-          prefix-key: "v2-rust"
+          prefix-key: "v3-rust"
           shared-key: "${{ inputs.os }}"
           cache-on-failure: true
           cache-all-crates: true
+      - name: Debug cache state (before build)
+        run: |
+          echo "=== target/ directory ==="
+          ls -la target/ 2>/dev/null | head -20 || echo "No target dir"
+          echo "=== fingerprint count ==="
+          ls target/.fingerprint/ 2>/dev/null | wc -l || echo "No fingerprints"
+          echo "=== registry/src ==="
+          ls ~/.cargo/registry/src/ 2>/dev/null | head -5 || echo "No registry src"
+          echo "=== sample dep fingerprint (memchr) ==="
+          ls -la target/.fingerprint/memchr-* 2>/dev/null || echo "No memchr fingerprint"
+        shell: bash
       - name: Build workspace
         run: cargo test --workspace --all-features --no-run ${{ inputs.exclude-crates && format('--exclude {0}', inputs.exclude-crates) || '' }}
+      - name: Debug cache state (after build)
+        run: |
+          echo "=== fingerprint count ==="
+          ls target/.fingerprint/ | wc -l
+          echo "=== sample dep fingerprint (memchr) ==="
+          ls -la target/.fingerprint/memchr-*
+        shell: bash
       - name: Upload build artifacts
         uses: actions/upload-artifact@v4
         with:
@@ -54,15 +72,33 @@ jobs:
       - uses: dtolnay/rust-toolchain@stable
       - uses: Swatinem/rust-cache@v2
         with:
-          prefix-key: "v2-rust"
+          prefix-key: "v3-rust"
           shared-key: "${{ inputs.os }}"
           save-if: false
           cache-all-crates: true
+      - name: Debug cache state (after cache restore, before artifact)
+        run: |
+          echo "=== target/ directory ==="
+          ls -la target/ 2>/dev/null | head -20 || echo "No target dir"
+          echo "=== fingerprint count ==="
+          ls target/.fingerprint/ 2>/dev/null | wc -l || echo "No fingerprints"
+          echo "=== registry/src ==="
+          ls ~/.cargo/registry/src/ 2>/dev/null | head -5 || echo "No registry src"
+          echo "=== sample dep fingerprint (memchr) ==="
+          ls -la target/.fingerprint/memchr-* 2>/dev/null || echo "No memchr fingerprint"
+        shell: bash
       - name: Download build artifacts
         uses: actions/download-artifact@v4
         with:
           name: build-${{ inputs.os }}
           path: target/
+      - name: Debug state (after artifact download)
+        run: |
+          echo "=== fingerprint count ==="
+          ls target/.fingerprint/ | wc -l
+          echo "=== sample dep fingerprint (memchr) ==="
+          ls -la target/.fingerprint/memchr-*
+        shell: bash
       - uses: actions/setup-python@v5
         with:
           python-version: "3.12"