Fix matrix generation; add local test

Author: build-failure

.github/workflows/sync-base-images.yml

@@ -1,6 +1,7 @@
 ---
 # Download Hetzner bootimages, import as Docker images, push to GHCR (multi-arch).
 # Runs monthly and on workflow_dispatch (manual). Image set from config/images.yaml.
+# Test the prepare step locally: ./test/scripts/test-prepare.sh (requires yq; optional jq to validate JSON).
 name: Sync Hetzner Base Images
 
 on:
@@ -31,14 +32,14 @@ jobs:
             echo "ERROR: config/images.yaml not found" >&2
             exit 1
           fi
-          json=$(bash scripts/list.sh --json)
+          json=$(bash scripts/list.sh --json | tr -d '\n')
           if [ -z "$json" ] || [ "$json" = "[]" ]; then
             echo "ERROR: list.sh produced no image/arch pairs (check config/images.yaml)" >&2
             exit 1
           fi
           echo "Matrix JSON length: ${#json} chars (output written to GITHUB_OUTPUT)"
-          # Single-line matrix required for strategy.matrix fromJson(); % must be escaped for GITHUB_OUTPUT
-          printf '%s\n' "matrix=${json//%/%25}" >> "$GITHUB_OUTPUT"
+          # Single-line matrix required: GITHUB_OUTPUT is newline-delimited and fromJson() needs valid JSON
+          printf 'matrix=%s\n' "${json//%/%25}" >> "$GITHUB_OUTPUT"
           images=$(yq -r '.images | keys | .[]' config/images.yaml | sort -u)
           echo "names<<NAMES_EOF" >> "$GITHUB_OUTPUT"
           echo "$images" >> "$GITHUB_OUTPUT"

.gitignore

@@ -1 +1,3 @@
 .env
+.github-output
+.local/

test/scripts/test-prepare.sh

@@ -0,0 +1,64 @@
+#!/usr/bin/env bash
+# Run the prepare job logic locally. Writes the same outputs to a file so you can
+# verify matrix/names and simulate fromJson() without running the full workflow.
+# Usage: ./test/scripts/test-prepare.sh [output-file]
+#   Default output: .github-output (repo root). Pass - to print only to stdout.
+
+set -euo pipefail
+
+REPO_ROOT="$(cd "$(dirname "$0")/../.." && pwd)"
+OUTPUT_FILE="${1:-$REPO_ROOT/.github-output}"
+
+cd "$REPO_ROOT"
+
+if [ ! -f config/images.yaml ]; then
+  echo "ERROR: config/images.yaml not found" >&2
+  exit 1
+fi
+
+if ! command -v yq &>/dev/null; then
+  echo "ERROR: yq not installed. Install from https://github.com/mikefarah/yq" >&2
+  exit 1
+fi
+
+# Same logic as .github/workflows/sync-base-images.yml prepare job
+json=$(bash scripts/list.sh --json | tr -d '\n')
+if [ -z "$json" ] || [ "$json" = "[]" ]; then
+  echo "ERROR: list.sh produced no image/arch pairs (check config/images.yaml)" >&2
+  exit 1
+fi
+
+echo "Matrix JSON length: ${#json} chars"
+
+# Build GITHUB_OUTPUT-style file (same as in workflow)
+if [ "$OUTPUT_FILE" = "-" ]; then
+  TARGET="/dev/stdout"
+else
+  TARGET="$OUTPUT_FILE"
+  : > "$TARGET"
+fi
+
+printf 'matrix=%s\n' "${json//%/%25}" >> "$TARGET"
+images=$(yq -r '.images | keys | .[]' config/images.yaml | sort -u)
+echo "names<<NAMES_EOF" >> "$TARGET"
+echo "$images" >> "$TARGET"
+echo "NAMES_EOF" >> "$TARGET"
+
+if [ "$OUTPUT_FILE" != "-" ]; then
+  echo "Wrote outputs to $OUTPUT_FILE"
+fi
+
+# Validate: simulate fromJson() on matrix (requires jq)
+if command -v jq &>/dev/null; then
+  if echo "$json" | jq -e . >/dev/null 2>&1; then
+    count=$(echo "$json" | jq 'length')
+    echo "Valid JSON matrix: $count entries (fromJson would succeed)"
+    echo "First 3 entries:"
+    echo "$json" | jq -c '.[:3][]'
+  else
+    echo "WARNING: matrix value is not valid JSON (fromJson would fail)" >&2
+    echo "Raw (first 120 chars): ${json:0:120}..." >&2
+  fi
+else
+  echo "Tip: install jq to validate that the matrix is valid JSON for fromJson()"
+fi