diff --git a/trio/_core/_run.py b/trio/_core/_run.py
index c5c16803b0..b2f3a65ddd 100644
--- a/trio/_core/_run.py
+++ b/trio/_core/_run.py
@@ -200,8 +200,7 @@ def collapse_exception_group(
         )
         return exceptions[0]
     elif modified:
-        # derive() returns Any for some reason.
-        return excgroup.derive(exceptions)  # type: ignore[no-any-return]
+        return excgroup.derive(exceptions)
     else:
         return excgroup
 
@@ -2358,7 +2357,9 @@ def my_done_callback(run_outcome):
     # spawn_system_task. We don't actually run any user code during
     # this time, so it shouldn't be possible to get an exception here,
     # except for a TrioInternalError.
-    next_send = None
+    next_send = cast(
+        EventResult, None
+    )  # First iteration must be `None`, every iteration after that is EventResult
     for tick in range(5):  # expected need is 2 iterations + leave some wiggle room
         if runner.system_nursery is not None:
             # We're initialized enough to switch to async guest ticks
@@ -2379,7 +2380,10 @@ def my_done_callback(run_outcome):
         # IOManager.get_events() if no I/O was waiting, which is
         # platform-dependent. We don't actually check for I/O during
         # this init phase because no one should be expecting any yet.
-        next_send = 0 if sys.platform == "win32" else ()
+        if sys.platform == "win32":
+            next_send = 0
+        else:
+            next_send = []
     else:  # pragma: no cover
         guest_state.unrolled_run_gen.throw(
             TrioInternalError(
diff --git a/trio/_core/_tests/test_run.py b/trio/_core/_tests/test_run.py
index 0b15b606fb..5c45cf828f 100644
--- a/trio/_core/_tests/test_run.py
+++ b/trio/_core/_tests/test_run.py
@@ -2066,7 +2066,7 @@ def check_function_returning_coroutine() -> Awaitable[object]:
         sniffio.current_async_library()
 
     @contextmanager
-    def alternate_sniffio_library():
+    def alternate_sniffio_library() -> Generator[None, None, None]:
         prev_token = sniffio.current_async_library_cvar.set("nullio")
         prev_library, sniffio.thread_local.name = sniffio.thread_local.name, "nullio"
         try:
diff --git a/trio/_threads.py b/trio/_threads.py
index 2780fb6446..24905cfbde 100644
--- a/trio/_threads.py
+++ b/trio/_threads.py
@@ -409,7 +409,6 @@ def callback(
         fn: Callable[..., RetT],
         args: tuple[object, ...],
     ) -> None:
-
         @disable_ki_protection
         def unprotected_fn() -> RetT:
             ret = fn(*args)