Add backpressure stack for agentic coding quality gates

PostToolUse hooks run after every file edit:
- Backend: ./mvnw compile (Checkstyle Google Style + javac)
- Frontend: vue-tsc --noEmit + oxlint + ESLint

Stop hook runs test suites when source files changed, blocks the
agent on failure and re-engages it to fix the issue. Output is
filtered to [ERROR] lines only for context efficiency.

Static analysis: Checkstyle (validate phase), SpotBugs (verify phase),
ArchUnit (9 hexagonal architecture rules as JUnit tests).

Fail-fast: Surefire skipAfterFailureCount=1, Vitest bail=1.
Test log noise suppressed via logback-test.xml (WARN level),
redirectTestOutputToFile, and trimStackTrace.

Existing Java sources reformatted to Google Style (2-space indent,
import order, Javadoc on public types).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.claude/hooks/frontend-check.sh

@@ -0,0 +1,37 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+# Read hook input from stdin (JSON with tool_input.file_path)
+INPUT=$(cat)
+FILE_PATH=$(echo "$INPUT" | python3 -c "import sys,json; print(json.load(sys.stdin).get('tool_input',{}).get('file_path',''))" 2>/dev/null || echo "")
+
+# Only run for TS/Vue files under frontend/
+case "$FILE_PATH" in
+    */frontend/src/*.ts|*/frontend/src/*.vue|frontend/src/*.ts|frontend/src/*.vue) ;;
+    *) exit 0 ;;
+esac
+
+cd "$CLAUDE_PROJECT_DIR/frontend"
+
+ERRORS=""
+
+# Type-check
+if OUTPUT=$(npx vue-tsc --noEmit 2>&1); then
+    :
+else
+    ERRORS+="Type-check failed:\n$OUTPUT\n\n"
+fi
+
+# Lint (without --fix — agent must self-correct)
+if OUTPUT=$(npx oxlint . 2>&1 && npx eslint . --cache 2>&1); then
+    :
+else
+    ERRORS+="Lint failed:\n$OUTPUT\n\n"
+fi
+
+if [[ -n "$ERRORS" ]]; then
+    ESCAPED=$(printf '%s' "$ERRORS" | python3 -c "import sys,json; print(json.dumps(sys.stdin.read()))")
+    echo "{\"hookSpecificOutput\":{\"hookEventName\":\"PostToolUse\",\"additionalContext\":$ESCAPED}}"
+else
+    echo '{"hookSpecificOutput":{"hookEventName":"PostToolUse","additionalContext":"✓ Frontend type-check + lint passed."}}'
+fi