fix(fabro-web): restore local watch rebuilds

Replace the unsupported Bun.watch call in the SPA build script with
node:fs.watch so `bun run dev` keeps running in local development.
Add a regression test that verifies watch mode stays alive until
interrupted.

apps/fabro-web/scripts/build.test.ts

@@ -0,0 +1,32 @@
+import { test, expect } from "bun:test";
+
+const root = Bun.fileURLToPath(new URL("..", import.meta.url));
+
+test("watch mode keeps running until interrupted", async () => {
+  const process = Bun.spawn([
+    "bun",
+    "run",
+    "scripts/build.ts",
+    "--watch",
+  ], {
+    cwd: root,
+    stdout: "pipe",
+    stderr: "pipe",
+  });
+
+  const result = await Promise.race([
+    process.exited.then((code) => ({ kind: "exited" as const, code })),
+    Bun.sleep(1000).then(() => ({ kind: "running" as const })),
+  ]);
+
+  if (result.kind === "exited") {
+    const stderr = await new Response(process.stderr).text();
+    const stdout = await new Response(process.stdout).text();
+    throw new Error(
+      `watch process exited unexpectedly with code ${result.code}\nstdout:\n${stdout}\nstderr:\n${stderr}`,
+    );
+  }
+
+  process.kill("SIGINT");
+  expect(await process.exited).toBe(0);
+});

apps/fabro-web/scripts/build.ts

@@ -1,3 +1,4 @@
+import { watch as fsWatch } from "node:fs";
 import { cp, mkdir, readFile, rm, writeFile } from "node:fs/promises";
 import { join, relative } from "node:path";
 
@@ -79,19 +80,37 @@ async function main() {
   }
 
   await buildOnce();
-  const watcher = Bun.watch({
-    paths: [join(rootPath, "app"), publicDir, templatePath],
-    async onChange() {
+  let building = false;
+  let rebuildQueued = false;
+
+  async function rebuild() {
+    if (building) {
+      rebuildQueued = true;
+      return;
+    }
+
+    building = true;
+    do {
+      rebuildQueued = false;
       try {
         await buildOnce();
       } catch (error) {
         console.error(error);
       }
-    },
-  });
+    } while (rebuildQueued);
+    building = false;
+  }
+
+  const watchers = [
+    fsWatch(join(rootPath, "app"), { recursive: true }, rebuild),
+    fsWatch(publicDir, { recursive: true }, rebuild),
+    fsWatch(templatePath, rebuild),
+  ];
 
   process.on("SIGINT", () => {
-    watcher.stop();
+    for (const watcher of watchers) {
+      watcher.close();
+    }
     process.exit(0);
   });
 }