diff --git a/src/bub/builtin/shell_manager.py b/src/bub/builtin/shell_manager.py
index 284c965b..68aef08d 100644
--- a/src/bub/builtin/shell_manager.py
+++ b/src/bub/builtin/shell_manager.py
@@ -53,6 +53,9 @@ def get(self, shell_id: str) -> ManagedShell:
         except KeyError as exc:
             raise KeyError(f"unknown shell id: {shell_id}") from exc
 
+    def release(self, shell_id: str) -> ManagedShell | None:
+        return self._shells.pop(shell_id, None)
+
     async def terminate(self, shell_id: str) -> ManagedShell:
         shell = self.get(shell_id)
         if shell.returncode is not None:
@@ -80,6 +83,7 @@ async def _finalize_shell(self, shell: ManagedShell) -> None:
         for task in shell.read_tasks:
             with contextlib.suppress(asyncio.CancelledError):
                 await task
+        self._shells.pop(shell.shell_id, None)
 
     async def _drain_stream(
         self,
diff --git a/tests/test_builtin_tools.py b/tests/test_builtin_tools.py
index 36c7e41e..cf731859 100644
--- a/tests/test_builtin_tools.py
+++ b/tests/test_builtin_tools.py
@@ -9,6 +9,8 @@
 from republic.core.errors import ErrorKind
 from republic.tools.executor import ToolExecutor
 
+import bub.builtin.tools as builtin_tools
+from bub.builtin.shell_manager import ShellManager
 from bub.builtin.tools import bash, bash_output, kill_bash
 
 
@@ -27,6 +29,28 @@ async def test_bash_returns_stdout_for_foreground_command(tmp_path) -> None:
     assert result == "hello"
 
 
+@pytest.mark.asyncio
+async def test_foreground_bash_releases_shell_from_shell_manager(tmp_path, monkeypatch) -> None:
+    manager = ShellManager()
+    monkeypatch.setattr(builtin_tools, "shell_manager", manager)
+
+    result = await bash.run(cmd=_python_shell("print('hello')"), context=_tool_context(tmp_path))
+
+    assert result == "hello"
+    assert manager._shells == {}
+
+
+@pytest.mark.asyncio
+async def test_foreground_bash_releases_shell_when_command_fails(tmp_path, monkeypatch) -> None:
+    manager = ShellManager()
+    monkeypatch.setattr(builtin_tools, "shell_manager", manager)
+
+    with pytest.raises(RuntimeError, match="command exited with code"):
+        await bash.run(cmd=_python_shell("import sys; sys.exit(2)"), context=_tool_context(tmp_path))
+
+    assert manager._shells == {}
+
+
 @pytest.mark.asyncio
 async def test_bash_non_zero_exit_is_returned_as_tool_error(tmp_path) -> None:
     command = _python_shell("import sys; print('boom'); sys.exit(7)")
@@ -71,7 +95,7 @@ async def test_background_bash_exposes_output_via_bash_output(tmp_path) -> None:
 
 
 @pytest.mark.asyncio
-async def test_kill_bash_terminates_background_process(tmp_path) -> None:
+async def test_kill_bash_terminates_background_process_and_releases_shell(tmp_path) -> None:
     started = await bash.run(
         cmd=_python_shell("import time; time.sleep(10)"),
         background=True,
@@ -80,11 +104,11 @@ async def test_kill_bash_terminates_background_process(tmp_path) -> None:
     shell_id = started.removeprefix("started: ").strip()
 
     killed = await kill_bash.run(shell_id=shell_id)
-    output = await bash_output.run(shell_id=shell_id)
 
     assert killed.startswith(f"id: {shell_id}\nstatus: exited\nexit_code: ")
     assert "exit_code: null" not in killed
-    assert output.startswith(f"id: {shell_id}\nstatus: exited\n")
+    with pytest.raises(KeyError, match="unknown shell id"):
+        await bash_output.run(shell_id=shell_id)
 
 
 @pytest.mark.asyncio