perf(kyberforge): scope skill-frontmatter to .apm/ and parallelize plugin sync

skill-frontmatter's files: pattern matched any SKILL.md, so it ran twice per
sync -- once on the .apm/ source and again on the compiled flat-mirror copy.
Scoped it to .apm/skills/ like its sibling hooks (skill-size-check,
vale-audit-prefilter-skill), which already only check the source.

sync-plugin-content.sh ran `apm pack` once per plugin, serially -- each
invocation is dominated by fixed CLI startup cost rather than per-plugin
work, so 6 plugins paid that cost 6 times over (~3.1s). Backgrounds the
per-plugin work instead, buffering each plugin's output so concurrent
DRIFT/FAIL messages can't interleave, then flushes in stable order after
`wait` (~1.3s, confirmed idempotent on a real sync).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01X7GvKuJfy2WrdBmUttV4DT

.pre-commit-config.yaml

@@ -149,7 +149,7 @@ repos:
         description: Ensure SKILL.md files have required frontmatter fields
         entry: bash
         language: system
-        files: 'SKILL\.md$'
+        files: '^plugins/[^/]+/\.apm/skills/[^/]+/SKILL\.md$'
         args:
           - -c
           - |

scripts/sync-plugin-content.sh

@@ -117,12 +117,17 @@ sync_hooks_json() {
   printf '%s\n' "$(cat "$src")" >"$dst"
 }
 
+# Runs entirely inside a backgrounded subshell (see the dispatch loop below), so
+# FAIL here is that subshell's own copy -- it never touches the parent's FAIL
+# and must be handed back via status_file instead.
 sync_one() {
-  local plugin_dir="${1%/}"
+  local plugin_dir="${1%/}" status_file="$2"
   local apm_dir="$plugin_dir/.apm"
+  FAIL=0
 
   if [[ ! -d "$apm_dir" ]]; then
     echo "SKIP $plugin_dir: no .apm/ directory" >&2
+    echo "$FAIL" >"$status_file"
     return 0
   fi
 
@@ -140,6 +145,7 @@ sync_one() {
     sed 's/^/    /' "$pack_log" >&2
     rm -f "$pack_log"
     FAIL=1
+    echo "$FAIL" >"$status_file"
     return 0
   fi
   rm -f "$pack_log"
@@ -148,6 +154,7 @@ sync_one() {
   if [[ -z "$bundle_dir" ]]; then
     echo "FAIL $plugin_dir: apm pack produced no bundle directory under $scratch" >&2
     FAIL=1
+    echo "$FAIL" >"$status_file"
     return 0
   fi
 
@@ -156,10 +163,26 @@ sync_one() {
     sync_dir "$plugin_dir" "$bundle_dir" "$d"
   done
   sync_hooks_json "$plugin_dir" "$bundle_dir"
+  echo "$FAIL" >"$status_file"
 }
 
-for plugin_dir in "$@"; do
-  sync_one "$plugin_dir"
+# Each plugin's `apm pack` is an independent CLI invocation dominated by fixed
+# process-startup cost, not by per-plugin work -- run them concurrently rather
+# than paying that startup cost N times serially. Output is buffered per plugin
+# (not streamed) so concurrent DRIFT/FAIL messages from different plugins never
+# interleave; it's flushed in stable $@ order once every job has finished.
+declare -a plugin_dirs=("$@")
+for plugin_dir in "${plugin_dirs[@]}"; do
+  name="$(basename "${plugin_dir%/}")"
+  (sync_one "$plugin_dir" "$SCRATCH_ROOT/$name.status") >"$SCRATCH_ROOT/$name.log" 2>&1 &
+done
+wait
+
+for plugin_dir in "${plugin_dirs[@]}"; do
+  name="$(basename "${plugin_dir%/}")"
+  cat "$SCRATCH_ROOT/$name.log" >&2
+  status="$(cat "$SCRATCH_ROOT/$name.status" 2>/dev/null || echo 1)"
+  [[ "$status" -ne 0 ]] && FAIL=1
 done
 
 if [[ "$FAIL" -ne 0 ]]; then