feat(gate): check.sh --brief prints a red lane's first error lines only

scripts/check.sh

@@ -7,6 +7,8 @@
 #
 #   bash scripts/check.sh        every lane (what a release requires, before e2e and the CVE scan)
 #   bash scripts/check.sh lint   the static lanes only: no tests, no build, no audits
+#   … --brief                    (either mode) a lane's output only when it fails, and only its first
+#                                error lines — for an agent, whose context the full log would flood
 #
 # Each lane runs even when an earlier one failed, and the summary names every red one: a gate that
 # stops at the first failure hides the second until the first is fixed. The backend lanes run in the
@@ -14,8 +16,15 @@
 # type checker or auditor without the real packages reports nonsense.
 set -u
 cd "$(dirname "$0")/.." || exit 2
-mode="${1:-all}"
-case "$mode" in all | lint) ;; *) echo "usage: scripts/check.sh [lint]" >&2; exit 2 ;; esac
+mode=all
+brief=0
+for arg in "$@"; do
+  case "$arg" in
+    all | lint) mode="$arg" ;;
+    --brief) brief=1 ;;
+    *) echo "usage: scripts/check.sh [lint] [--brief]" >&2; exit 2 ;;
+  esac
+done
 
 export MSYS_NO_PATHCONV=1 # Git Bash: do not rewrite the in-container paths below
 TESTCOMPOSE=backend/docker-compose.test.yml
@@ -23,8 +32,29 @@ failed=()
 lane() { # lane <name> <command…> — run it, remember a failure, never stop
   local name="$1"
   shift
-  echo ">> $name…"
-  "$@" || failed+=("$name")
+  if [ "$brief" = 0 ]; then
+    echo ">> $name…"
+    "$@" || failed+=("$name")
+    return 0
+  fi
+  local out
+  out="$(mktemp)"
+  if "$@" >"$out" 2>&1; then
+    echo ">> $name: ok"
+  else
+    failed+=("$name")
+    echo ">> $name: FAILED"
+    brief_excerpt "$out"
+  fi
+  rm -f "$out"
+}
+# The lines that say what broke: the first 20 error-looking ones, each with the two lines after it
+# (knip names the file on the line after "Unused files"); a log with none of them (a tool that
+# words its failures some other way) shows its tail instead, which is where a summary sits.
+brief_excerpt() {
+  local hits
+  hits="$(grep -E -i -A 2 -m 20 'error|fail|✗|×|warn|would reformat|unused|vulnerab|found [0-9]' "$1")"
+  if [ -n "$hits" ]; then printf '%s\n' "$hits"; else tail -n 20 "$1"; fi
 }
 
 # --- static lanes ------------------------------------------------------------------------------------