perf: incremental cargo builds, skip apt when cached

- Build in $HOME/archy to reuse target/ cache across CI runs
- Skip apt-get install when ISO build deps already present
- Cargo tests also use persistent target dir

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.gitea/workflows/build-iso-dev.yml

@@ -28,17 +28,28 @@ jobs:
 
       - name: Install ISO build dependencies
         run: |
+          # Skip apt if packages already installed (persistent runner)
+          if dpkg -s debootstrap squashfs-tools xorriso isolinux syslinux-common mtools \
+               grub-efi-amd64-bin grub-pc-bin grub-common >/dev/null 2>&1; then
+            echo "ISO build deps already installed, skipping apt"
+          else
             sudo apt-get update -qq
             sudo apt-get install -y -qq \
               debootstrap squashfs-tools xorriso \
               isolinux syslinux-common mtools \
               grub-efi-amd64-bin grub-pc-bin grub-common
+          fi
 
-      - name: Build backend
+      - name: Build backend (incremental)
         run: |
           source $HOME/.cargo/env 2>/dev/null || true
+          # Build in persistent repo dir to reuse target/ cache
+          cd "$HOME/archy"
           export GIT_HASH=$(git rev-parse --short HEAD)
           cargo build --release --manifest-path core/Cargo.toml
+          # Copy binary to workspace for downstream steps
+          mkdir -p "$GITHUB_WORKSPACE/core/target/release"
+          cp core/target/release/archipelago "$GITHUB_WORKSPACE/core/target/release/"
 
       - name: Build frontend
         run: cd neode-ui && npm ci && npm run build
@@ -52,6 +63,7 @@ jobs:
       - name: Run container orchestration unit tests
         run: |
           source $HOME/.cargo/env 2>/dev/null || true
+          cd "$HOME/archy"
           echo "=== Container crate tests ==="
           cargo test -p archipelago-container --no-fail-fast --manifest-path core/Cargo.toml
           echo ""