perf(ci): fold the matrix job into the image job and stream its output

Computing the distro list no longer justifies a runner of its own: it is
two steps, and the job that consumes them already checks the repository
out. The workflow now occupies one runner instead of seven.

The step also went silent for minutes at a time, printing five pids and
then nothing until every build had finished. Each build's output is piped
through a [distro][HH:MM:SS] stamp as it arrives, so the log shows what is
happening while it happens; tee still files the per-distro logs for the
artifact, and the replay block at the end is gone as duplication.

A pipeline hands $! the pid of tee rather than of the build, which would
have swallowed every failure, so each build runs in a subshell under
pipefail and wait reads that.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

.github/workflows/call-images-build-ci.yml

@@ -41,25 +41,8 @@ concurrency:
   cancel-in-progress: false
 
 jobs:
-  prepare:
-    name: 📋 Build Matrix
-    runs-on: ubuntu-latest
-    outputs:
-      matrix: ${{ steps.out.outputs.matrix }}
-      image_tag: ${{ steps.out.outputs.image_tag }}
-    steps:
-      - uses: actions/checkout@v7.0.0
-
-      - name: 📦 Install jq
-        run: ./scripts/install/apt.sh jq
-
-      - name: 🧮 Compute matrix JSON
-        id: out
-        run: scripts/github/runner/images_build_outputs.sh "${{ inputs.distros }}" "${{ inputs.image_tag }}"
-
   build:
     name: 💿 Image
-    needs: prepare
     runs-on: ubuntu-latest
     permissions:
       contents: read
@@ -81,6 +64,13 @@ jobs:
           persist-credentials: false
           allow-unsafe-pr-checkout: ${{ inputs.allow_unsafe_checkout }}
 
+      - name: 📦 Install jq
+        run: ./scripts/install/apt.sh jq
+
+      - name: 🧮 Compute the distro list and image tag
+        id: out
+        run: scripts/github/runner/images_build_outputs.sh "${{ inputs.distros }}" "${{ inputs.image_tag }}"
+
       - name: 💽 Disk pressure (start)
         shell: bash
         run: bash scripts/github/runner/disk_pressure_report.sh START
@@ -129,8 +119,8 @@ jobs:
         env:
           GITHUB_REPOSITORY_OWNER: ${{ steps.owner.outputs.owner }}
           BUILD_CONTEXT_DIR: _src
-          INFINITO_DISTROS: ${{ join(fromJson(needs.prepare.outputs.matrix), ' ') }}
-          IMAGE_TAG: ${{ needs.prepare.outputs.image_tag }}
+          INFINITO_DISTROS: ${{ join(fromJson(steps.out.outputs.matrix), ' ') }}
+          IMAGE_TAG: ${{ steps.out.outputs.image_tag }}
           USE_NIX_TOKEN: ${{ !(github.event_name == 'pull_request_target' && github.event.pull_request.head.repo.full_name != github.repository) }}
           NIX_GITHUB_TOKEN: ${{ github.token }}
           MAX_ATTEMPTS: "7"

scripts/image/push_all.sh

@@ -12,21 +12,15 @@ if ((${#distros[@]} == 0)); then
 	read -r -a distros <<<"${INFINITO_DISTROS}"
 fi
 
-log_dir="${INFINITO_BUILD_LOG_DIR:-${repo_root}/build/image-logs}"
+log_dir="${BUILD_LOG_DIR:-${repo_root}/build/image-logs}"
 mkdir -p "${log_dir}"
 
-group_open() {
-	if [[ -n "${GITHUB_ACTIONS:-}" ]]; then
-		echo "::group::$1"
-	else
-		echo "──────── $1 ────────"
-	fi
-}
-
-group_close() {
-	if [[ -n "${GITHUB_ACTIONS:-}" ]]; then
-		echo "::endgroup::"
-	fi
+stamp() {
+	local distro="$1"
+	local line
+	while IFS= read -r line; do
+		printf '[%s][%(%H:%M:%S)T] %s\n' "${distro}" -1 "${line}"
+	done
 }
 
 # shellcheck source=scripts/meta/env/load.sh
@@ -48,10 +42,13 @@ for distro in "${distros[@]}"; do
 		gap="${gap_next}"
 	fi
 
-	MATRIX_DISTRO="${distro}" \
-		bash "${script_dir}/push.sh" >"${log_dir}/${distro}.log" 2>&1 &
+	(
+		set -o pipefail
+		MATRIX_DISTRO="${distro}" bash "${script_dir}/push.sh" 2>&1 |
+			stamp "${distro}" |
+			tee "${log_dir}/${distro}.log"
+	) &
 	pids+=("$!")
-	echo "    → ${distro} started as pid $!"
 	started=$((started + 1))
 done
 
@@ -68,12 +65,6 @@ for pid in "${pids[@]}"; do
 	index=$((index + 1))
 done
 
-for distro in "${distros[@]}"; do
-	group_open "${distro}"
-	cat "${log_dir}/${distro}.log" || true # nocheck: shell-or-true -- a missing log must not mask the build verdict below
-	group_close
-done
-
 if ((${#failed[@]} > 0)); then
 	echo "❌ Failed distros: ${failed[*]}"
 	exit 1