workflows: add build workflow

wip ...

Author: fvalette

.github/workflows/build.yml

@@ -0,0 +1,86 @@
+# SPDX-FileCopyrightText: 2026 H2Lab Development Team
+# SPDX-License-Identifier: Apache-2.0
+
+name: Build cross-toolchain
+
+on:
+  push:
+    branches:
+      - main
+
+jobs:
+
+  changes:
+    runs-on: ubuntu-latest
+    permissions:
+      pull-requests: read
+    outputs:
+      devcontainer: ${{ steps.filter.outputs.devcontainer }}
+      configs: ${{ steps.filter.outputs.configs }}
+      configs_files: ${{ steps.filter.outputs.configs_files }}
+    steps:
+      - uses: dorny/paths-filter@v4
+        id: filter
+        with:
+          filters: |
+            devcontainer:
+              - '.devcontainer/devcontainer.json'
+            configs:
+              - 'configs/**'
+
+  prebuilt:
+    needs: changes
+    if: ${{ needs.changes.outputs.devcontainer == 'true' }}
+    runs-on: ubuntu-latest
+    permissions:
+      packages: write
+    steps:
+      - uses: actions/checkout@v6
+
+      - name: Login to GitHub Container Registry
+        uses: docker/login-action@v4
+        with:
+          registry: ghcr.io
+          username: ${{ github.repository_owner }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Pre-build dev container image
+        uses: devcontainers/ci@v0.3
+        with:
+          imageName: ghcr.io/camelot-os/prebuilt-ctng-devcontainer
+          cacheFrom: ghcr.io/camelot-os/prebuilt-ctng-devcontainer
+          push: always
+
+  cache_update:
+    needs: [changes, prebuilt]
+    # if: ${{ !cancelled() && needs.changes.outputs.configs == 'true' }}
+    if: ${{ !cancelled() }}
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v6
+      - name: Restore cached sources dir
+        id: cache-restore
+        uses: actions/cache/restore@v5
+        with:
+          path: |
+            src
+          key: package-sources
+      - name: Download sources
+        uses: devcontainers/ci@v0.3
+        with:
+          cacheFrom: ghcr.io/camelot-os/prebuilt-ctng-devcontainer
+          push: never
+          runCmd: |
+            DEFCONFIG=configs/arm-none-eabi.defconfig ct-ng defconfig
+            # patch config for donwload only in cache directory
+            sed -i `s/.*CT_ONLY_DOWNLOAD.*/CT_ONLY_DOWNLOAD=y/` .config
+            sed -i `s/.*CT_LOCAL_TARBALLS_DIR.*/CT_LOCAL_TARBALLS_DIR=src/` .config
+            sed -i `s/.*CT_SAVE_TARBALLS.*/CT_SAVE_TARBALLS=y/` .config
+            ct-ng build
+      - name: Save cached sources dir
+        id: cache-save
+        uses: actions/cache/save@v5
+        with:
+          path: |
+            src
+          key: ${{ steps.cache-restore.outputs.cache-primary-key }}