refactor(browser): split act route modules and dedupe path guards

src/browser/routes/output-paths.ts

@@ -0,0 +1,31 @@
+import fs from "node:fs/promises";
+import { resolveWritablePathWithinRoot } from "./path-output.js";
+import type { BrowserResponse } from "./types.js";
+
+export async function ensureOutputRootDir(rootDir: string): Promise<void> {
+  await fs.mkdir(rootDir, { recursive: true });
+}
+
+export async function resolveWritableOutputPathOrRespond(params: {
+  res: BrowserResponse;
+  rootDir: string;
+  requestedPath: string;
+  scopeLabel: string;
+  defaultFileName?: string;
+  ensureRootDir?: boolean;
+}): Promise<string | null> {
+  if (params.ensureRootDir) {
+    await ensureOutputRootDir(params.rootDir);
+  }
+  const pathResult = await resolveWritablePathWithinRoot({
+    rootDir: params.rootDir,
+    requestedPath: params.requestedPath,
+    scopeLabel: params.scopeLabel,
+    defaultFileName: params.defaultFileName,
+  });
+  if (!pathResult.ok) {
+    params.res.status(400).json({ error: pathResult.error });
+    return null;
+  }
+  return pathResult.path;
+}