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

frontend/src/lib/gates.snapshot.json

@@ -1436,7 +1436,8 @@
         "e2e/helpers.ts",
         "e2e/nav.spec.ts",
         "e2e/player.spec.ts",
-        "e2e/settings.spec.ts"
+        "e2e/settings.spec.ts",
+        "e2e/speed.measure.ts"
       ],
       "js configs": ["eslint.config.js", "postcss.config.js"],
       "lib tests": [
@@ -2309,16 +2310,40 @@
     "scripts/check.sh": [
       "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 ;;",
+      "  esac",
+      "done",
       "export MSYS_NO_PATHCONV=1 # Git Bash: do not rewrite the in-container paths below",
       "TESTCOMPOSE=backend/docker-compose.test.yml",
       "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 \"$out\"",
+      "}",
+      "brief_excerpt() {",
+      "  local hits",
+      "  hits=\"$(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",
       "}",
       "ruff_pinned() {",
       "  local pin host",

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 ------------------------------------------------------------------------------------