frobar: Proper handling of EOF

I now get why the Python documentation really insists you use
.communicate().

hm/desktop/frobar/frobar/common.py

@@ -375,12 +375,18 @@ class Screen(ComposableText):
                     markup = self.get_markup()
                     # sys.stdout.write(markup)  # DEBUG
                     proc.stdin.write(markup.encode())
+                    try:
+                        await proc.stdin.drain()
+                    except BrokenPipeError:
+                        log.error("zelbar: broken pipe, killing")
+                        proc.kill()
+                        return
                     await self.refresh.wait()
                     self.refresh.clear()
 
             async def action_handler(proc: asyncio.subprocess.Process) -> None:
                 assert proc.stdout
-                while proc.returncode is None:
+                while not proc.stdout.at_eof():
                     line = await proc.stdout.readline()
                     try:
                         command = line.decode().strip()
@@ -393,6 +399,8 @@ class Screen(ComposableText):
                         log.error("Unknown command: %s", command)
                         continue
                     callback()
+                log.error("zelbar: EOF reached, killing")
+                proc.kill()
 
             refresher_task = self.bar.add_long_running_task(refresher(proc))
             action_handler_task = self.bar.add_long_running_task(action_handler(proc))