initial: action/cascade-from @v1

README.md

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+# action/cascade-from
+
+Composite Gitea Action that bumps a `FROM <image>:<tag>` line in a target
+repo's Dockerfile, then commits and pushes. The target repo's CI fires on
+that push, rebuilding against the new base.
+
+The only consumer today is `fritzlab/base` triggering a rebuild of
+`fritzlab/runner` whenever the base image changes. This action is the
+generalization of that pattern.
+
+## Usage
+
+```yaml
+- uses: actions/checkout@v4
+- uses: https://code.fritzlab.net/action/image-build@v1
+  with:
+    image: code.fritzlab.net/fritzlab/base
+- uses: https://code.fritzlab.net/action/image-push@v1
+  with:
+    image: code.fritzlab.net/fritzlab/base
+    token: ${{ secrets.CI_BOT_TOKEN }}
+    org: fritzlab
+    name: base
+- uses: https://code.fritzlab.net/action/cascade-from@v1
+  with:
+    target-repo: fritzlab/runner
+    image: code.fritzlab.net/fritzlab/base
+    token: ${{ secrets.CI_BOT_TOKEN }}
+```
+
+## Inputs
+
+| Name | Required | Default | Description |
+|---|---|---|---|
+| `target-repo` | yes | — | Target repo to edit (e.g. `fritzlab/runner`). |
+| `image` | yes | — | Image to look for in the FROM line. |
+| `tag` | no | `github.run_number` | New tag to write into FROM. |
+| `file` | no | `Dockerfile` | File inside target-repo to edit. |
+| `token` | yes | — | `CI_BOT_TOKEN` with write to target-repo. |
+| `host` | no | `code.fritzlab.net` | Gitea host without protocol. |
+| `message` | no | `bump <name> to #<tag>` | Commit message override. |
+
+## Behavior
+
+1. Shallow-clone target-repo to a temp dir.
+2. `sed -i "s|^FROM <image>:.*|FROM <image>:<tag>|" <file>`.
+3. Verify sed actually matched a line — fail if not (catches typos in image
+   name).
+4. If no diff (target already on this tag): exit 0 silently.
+5. Otherwise commit + push to `main` with rebase-on-conflict retry up to
+   3 times.
+
+## Notes
+
+- Only matches lines starting with `FROM <image>:` (anchored to start). Multi-stage
+  Dockerfiles with a non-anchored `FROM <image>:tag AS stage` will be missed —
+  add the AS-aware pattern as a future enhancement if needed.
+- Pushing to target-repo triggers its CI, which produces a new image of its
+  own. There is no end-to-end orchestration: the upstream repo's CI completes
+  the moment cascade-from pushes, regardless of whether the downstream build
+  succeeds.

action.yaml

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+name: Cascade FROM bump
+description: |
+  Bump a `FROM <image>:<tag>` line in a target repo's Dockerfile to trigger that
+  repo's CI. Used when a base image rebuild needs to cascade rebuilds in
+  downstream image repos.
+inputs:
+  target-repo:
+    description: Target repo to edit (e.g. fritzlab/runner)
+    required: true
+  image:
+    description: Image referenced in the target file's FROM line (e.g. code.fritzlab.net/fritzlab/base)
+    required: true
+  tag:
+    description: New tag. Defaults to github.run_number when empty.
+    required: false
+    default: ''
+  file:
+    description: File path inside target-repo to edit
+    required: false
+    default: Dockerfile
+  token:
+    description: CI_BOT_TOKEN with write access to target-repo
+    required: true
+  host:
+    description: Gitea host (without protocol)
+    required: false
+    default: code.fritzlab.net
+  message:
+    description: Commit message override. Defaults to "bump <image> to #<tag>".
+    required: false
+    default: ''
+runs:
+  using: composite
+  steps:
+    - name: Clone, edit, push
+      shell: bash
+      env:
+        TARGET_REPO: ${{ inputs.target-repo }}
+        IMAGE: ${{ inputs.image }}
+        TAG_INPUT: ${{ inputs.tag }}
+        FILE: ${{ inputs.file }}
+        TOKEN: ${{ inputs.token }}
+        HOST: ${{ inputs.host }}
+        MESSAGE: ${{ inputs.message }}
+        RUN_NUMBER: ${{ github.run_number }}
+      run: |
+        set -euo pipefail
+
+        TAG="${TAG_INPUT:-$RUN_NUMBER}"
+        NAME="$(basename "$IMAGE")"
+        MSG="${MESSAGE:-bump ${NAME} to #${TAG}}"
+
+        WORK="$(mktemp -d)"
+        trap 'rm -rf "$WORK"' EXIT
+
+        git clone --depth 1 "https://ci-bot:${TOKEN}@${HOST}/${TARGET_REPO}.git" "$WORK"
+        cd "$WORK"
+        git config user.name ci-bot
+        git config user.email ci-bot@fritzlab.net
+
+        if [ ! -f "$FILE" ]; then
+          echo "FATAL: ${FILE} not found in ${TARGET_REPO}"
+          exit 1
+        fi
+
+        # Escape forward slashes for sed pattern
+        ESC_IMAGE="${IMAGE//\//\\/}"
+        sed -i "s|^FROM ${IMAGE}:.*|FROM ${IMAGE}:${TAG}|" "$FILE"
+
+        if ! grep -q "^FROM ${IMAGE}:${TAG}\b" "$FILE"; then
+          echo "FATAL: sed did not match a FROM line for ${IMAGE} in ${FILE}"
+          grep "^FROM" "$FILE" || true
+          exit 1
+        fi
+
+        if git diff --quiet; then
+          echo "${TARGET_REPO} already on ${NAME}:${TAG}, skipping"
+          exit 0
+        fi
+
+        git add "$FILE"
+        git commit -m "$MSG"
+
+        ATTEMPTS=0
+        until git push origin main; do
+          ATTEMPTS=$((ATTEMPTS + 1))
+          if [ "$ATTEMPTS" -ge 3 ]; then
+            echo "FATAL: push to ${TARGET_REPO} failed after ${ATTEMPTS} attempts"
+            exit 1
+          fi
+          echo "push rejected, attempt ${ATTEMPTS}; rebasing and retrying"
+          git pull --rebase origin main
+          sleep $((ATTEMPTS * 2))
+        done
+
+        echo "cascaded ${NAME}:${TAG} → ${TARGET_REPO}"