Fix resize and poller races; add coverage

- Fix resize message handling when session already exists
- Guard poller selector.modify against removed fds
- Handle send_bytes race when master_fd closes
- Add tests for resize edge case, poller write KeyError, send_bytes race

src/textual_webterm/local_server.py

@@ -346,9 +346,9 @@ class LocalServer:
         if msg_type == "stdin":
             await self._handle_stdin(envelope, route_key, ws)
         elif msg_type == "resize":
-            if not session_created and await self._handle_resize(envelope, route_key, ws):
-                session_created = True
-            elif session_created:
+            if not session_created:
+                session_created = await self._handle_resize(envelope, route_key, ws)
+            else:
                 await self._handle_resize(envelope, route_key, ws)
         elif msg_type == "ping":
             await self._handle_ping(envelope, route_key, ws)

src/textual_webterm/poller.py

@@ -62,7 +62,17 @@ class Poller(Thread):
             self._write_queues[file_descriptor] = deque()
         new_write = Write(data)
         self._write_queues[file_descriptor].append(new_write)
-        self._selector.modify(file_descriptor, selectors.EVENT_READ | selectors.EVENT_WRITE)
+        try:
+
+            self._selector.modify(file_descriptor, selectors.EVENT_READ | selectors.EVENT_WRITE)
+
+        except KeyError:
+
+            # File descriptor removed concurrently
+
+            new_write.done_event.set()
+
+            return
         await new_write.done_event.wait()
 
     def set_loop(self, loop: asyncio.AbstractEventLoop) -> None:

src/textual_webterm/terminal_session.py

@@ -253,9 +253,13 @@ class TerminalSession(Session):
                 os.close(fd)
 
     async def send_bytes(self, data: bytes) -> bool:
-        if self.master_fd is None:
+        fd = self.master_fd
+        if fd is None:
+            return False
+        try:
+            await self.poller.write(fd, data)
+        except (KeyError, OSError):
             return False
-        await self.poller.write(self.master_fd, data)
         return True
 
     async def send_meta(self, data: Meta) -> bool: