test: add check-ui guards for behaviour a successful build does not demonstrate

Makefile

@@ -1,4 +1,4 @@
-.PHONY: build clean ui
+.PHONY: build clean ui check-ui check-ui-assets check-ui-locales check-ui-plugin-i18n
 
 VERSION=2.0.3
 BIN=answer
@@ -47,6 +47,22 @@ check:
 test:
 	@$(GO) test ./internal/repo/repo_test
 
+# Frontend checks for behaviour a successful build does not demonstrate.
+# Each guards a runtime failure that leaves every build step reporting success.
+check-ui: check-ui-assets check-ui-locales check-ui-plugin-i18n
+
+# The server reads the built asset paths out of index.html.
+check-ui-assets:
+	@./script/check-built-assets.sh
+
+# The app loads languages other than the default one through a dynamic import.
+check-ui-locales:
+	@cd ui && pnpm check-locales
+
+# Plugin translations register while modules evaluate, in bundler-decided order.
+check-ui-plugin-i18n:
+	@cd ui && pnpm check-plugin-i18n
+
 # clean all build result
 clean:
 	@$(GO) clean ./...

script/check-built-assets.sh

@@ -0,0 +1,104 @@
+#!/bin/bash
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+
+# Builds the frontend and asserts the server can still find the built assets
+# inside index.html. See internal/controller/template_controller_test.go for
+# why that is not implied by a successful build.
+#
+# --skip-build   reuse an existing ui/build, do not rebuild
+# --self-check   additionally rewrite ui/build/index.html so a script
+#                or stylesheet tag is missing, and confirm the check
+#                fails on the missing asset. Restores the real build
+#                output afterwards.
+
+set -euo pipefail
+
+REPO_ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+INDEX_HTML="$REPO_ROOT/ui/build/index.html"
+TEST_PACKAGE="./internal/controller/"
+TEST_NAME="TestGetStyleResolvesBuiltAssets"
+
+list_output="$(cd "$REPO_ROOT" && go test "$TEST_PACKAGE" -list "^${TEST_NAME}$" 2>&1)"
+if ! grep -qx "$TEST_NAME" <<<"$list_output"; then
+  echo "no test named $TEST_NAME in $TEST_PACKAGE; go test -run with a stale/renamed test name matches nothing and still exits 0, which would turn this check into a silent no-op" >&2
+  exit 1
+fi
+
+skip_build=0
+self_check=0
+for arg in "$@"; do
+  case "$arg" in
+    --skip-build) skip_build=1 ;;
+    --self-check) self_check=1 ;;
+    *) echo "unknown option: $arg" >&2; exit 2 ;;
+  esac
+done
+
+run_check() {
+  (cd "$REPO_ROOT" && go test -count=1 "$TEST_PACKAGE" -run "$TEST_NAME" "$@")
+}
+
+if [ "$skip_build" -eq 0 ]; then
+  echo "==> building frontend"
+  (cd "$REPO_ROOT/ui" && pnpm build)
+fi
+
+if [ ! -f "$INDEX_HTML" ]; then
+  echo "no built index.html at $INDEX_HTML; run without --skip-build" >&2
+  exit 1
+fi
+
+echo "==> checking the server can parse the built asset tags"
+run_check -v
+
+if [ "$self_check" -eq 0 ]; then
+  exit 0
+fi
+
+# Confirm the check actually fails when a required asset is missing from
+# the build output. Without this, a check that silently stopped asserting
+# anything would look identical to a passing one.
+backup="$(mktemp)"
+cp "$INDEX_HTML" "$backup"
+trap 'cp "$backup" "$INDEX_HTML"; rm -f "$backup"' EXIT
+
+expect_failure() {
+  local label="$1"
+  local html="$2"
+  printf '%s' "$html" > "$INDEX_HTML"
+  echo "==> self-check: expecting failure on $label"
+  if run_check >/dev/null 2>&1; then
+    echo "SELF-CHECK FAILED: the check passed on $label, so it is not guarding anything" >&2
+    exit 1
+  fi
+  echo "    check failed as expected"
+}
+
+expect_failure "stylesheet link but no script src" \
+  '<!doctype html><html><head><meta charset="utf-8"/><link rel="stylesheet" crossorigin href="/static/css/index-e5f6a7b8.css"></head><body><div id="root"></div></body></html>'
+
+expect_failure "script src but no stylesheet link" \
+  '<!doctype html><html><head><meta charset="utf-8"/><script type="module" crossorigin src="/static/js/index-a1b2c3d4.js"></script></head><body><div id="root"></div></body></html>'
+
+expect_failure "only an inline script, no src" \
+  '<!doctype html><html><head><meta charset="utf-8"/><link rel="stylesheet" crossorigin href="/static/css/index-e5f6a7b8.css"></head><body><div id="root"></div><script>window.__inline=1;</script></body></html>'
+
+expect_failure "manifest link but no stylesheet link" \
+  '<!doctype html><html><head><meta charset="utf-8"/><script type="module" crossorigin src="/static/js/index-a1b2c3d4.js"></script><link rel="manifest" href="/manifest.json"></head><body><div id="root"></div></body></html>'
+
+echo "==> self-check passed"

ui/package.json

@@ -12,6 +12,8 @@
     "build:packages": "pnpm -r --filter=./src/plugins/* run build",
     "clean": "rm -rf node_modules && rm -rf src/plugins/**/node_modules",
     "analyze": "source-map-explorer 'build/static/js/*.js'",
+    "check-locales": "node ./scripts/check-locale-resolution.js",
+    "check-plugin-i18n": "node ./scripts/check-plugin-i18n-order.js",
     "setup-lint": "node scripts/setup-eslint.js && cd .. && husky install",
     "lint": "eslint . --cache --fix --ext .ts,.tsx",
     "prettier": "prettier --write \"src/**/*.{ts,tsx,css,scss,md}\"",