diff --git a/bot_bottle/api.py b/bot_bottle/api.py
index a7c4130..bda2840 100644
--- a/bot_bottle/api.py
+++ b/bot_bottle/api.py
@@ -20,7 +20,7 @@ call sites in ``lifecycle.py`` are unchanged.
 
 from __future__ import annotations
 
-from typing import Sequence
+from typing import Sequence, cast
 
 from .backend import BottleSpec
 from .backend.freeze import CommitCancelled, get_freezer
@@ -102,7 +102,7 @@ def start_headless(
             headless_prompt_text=prompt,
         )
     except Die as exc:
-        raise BottleError(exc.message, exit_code=exc.code) from exc
+        raise BottleError(exc.message, exit_code=cast(int, exc.code)) from exc
     if exit_code != 0:
         raise BottleError(
             f"agent exited {exit_code} (slug={slug!r})", exit_code=exit_code
@@ -155,7 +155,7 @@ def resume_headless(
             headless_prompt_text=prompt,
         )
     except Die as exc:
-        raise BottleError(exc.message, exit_code=exc.code) from exc
+        raise BottleError(exc.message, exit_code=cast(int, exc.code)) from exc
     if exit_code != 0:
         raise BottleError(
             f"agent exited {exit_code} resuming {slug!r}", exit_code=exit_code
@@ -174,7 +174,7 @@ def freeze(slug: str, *, backend_name: str | None = None) -> None:
     except CommitCancelled as exc:
         raise BottleError(f"freeze cancelled for {slug!r}") from exc
     except Die as exc:
-        raise BottleError(exc.message, exit_code=exc.code) from exc
+        raise BottleError(exc.message, exit_code=cast(int, exc.code)) from exc
 
 
 def destroy(slug: str, *, backend_name: str | None = None) -> None:
@@ -194,7 +194,7 @@ def destroy(slug: str, *, backend_name: str | None = None) -> None:
         # context manager; no persistent VM survives, so nothing extra is
         # needed at destroy time beyond the state-dir removal below.
     except Die as exc:
-        raise BottleError(exc.message, exit_code=exc.code) from exc
+        raise BottleError(exc.message, exit_code=cast(int, exc.code)) from exc
     clear_preserve_marker(slug)
     cleanup_state(slug)
 
diff --git a/tests/unit/test_api.py b/tests/unit/test_api.py
index 6160919..454008f 100644
--- a/tests/unit/test_api.py
+++ b/tests/unit/test_api.py
@@ -56,7 +56,7 @@ class TestStartHeadless(unittest.TestCase):
             "bot_bottle.api._launch_bottle", return_value=("implementer-abc12", 0)
         ).start()
         patch(
-            "bot_bottle.api._uniquify_label_headless", side_effect=lambda lbl: lbl
+            "bot_bottle.api._uniquify_label_headless", side_effect=str
         ).start()
         self.addCleanup(patch.stopall)