e2e: add console-error gate fixture with allowlist

tests/e2e/fixtures/console-allowlist.json

@@ -0,0 +1,3 @@
+{
+  "patterns": []
+}

tests/e2e/fixtures/console-gate.ts

@@ -0,0 +1,70 @@
+import { test as base, expect } from "@playwright/test";
+import fs from "node:fs";
+import path from "node:path";
+
+interface AllowlistEntry {
+  pattern: string;
+  reason: string;
+}
+
+interface Allowlist {
+  patterns: AllowlistEntry[];
+}
+
+const ALLOWLIST_PATH = path.join(__dirname, "console-allowlist.json");
+
+function loadAllowlist(): RegExp[] {
+  const raw = fs.readFileSync(ALLOWLIST_PATH, "utf8");
+  const parsed: Allowlist = JSON.parse(raw);
+  for (const entry of parsed.patterns) {
+    if (!entry.reason || entry.reason.trim() === "") {
+      throw new Error(
+        `console-allowlist.json: pattern ${JSON.stringify(entry.pattern)} has no reason`
+      );
+    }
+  }
+  return parsed.patterns.map((e) => new RegExp(e.pattern));
+}
+
+const allowlist = loadAllowlist();
+
+function isAllowed(message: string): boolean {
+  return allowlist.some((re) => re.test(message));
+}
+
+interface ConsoleGateFixtures {
+  consoleMessages: string[];
+}
+
+export const test = base.extend<ConsoleGateFixtures>({
+  consoleMessages: async ({ page }, use, testInfo) => {
+    const messages: string[] = [];
+    page.on("console", (msg) => {
+      const type = msg.type();
+      if (type !== "error" && type !== "warning") return;
+      const text = `[${type}] ${msg.text()}`;
+      if (isAllowed(text)) return;
+      messages.push(text);
+    });
+    page.on("pageerror", (err) => {
+      const text = `[pageerror] ${err.message}`;
+      if (!isAllowed(text)) messages.push(text);
+    });
+
+    await use(messages);
+
+    if (messages.length > 0) {
+      testInfo.attachments.push({
+        name: "console-violations.txt",
+        contentType: "text/plain",
+        body: Buffer.from(messages.join("\n"), "utf8"),
+      });
+      throw new Error(
+        `Console gate: ${messages.length} disallowed message(s):\n` +
+          messages.map((m) => `  ${m}`).join("\n")
+      );
+    }
+  },
+});
+
+export { expect };