fix: revert unnecessary sandbox backend changes to fix type errors

Align wasm_backend.py, e2b_backend.py, and test_wasm_backend.py with
version-sandboxes branch. The changes on this branch introduced type
errors by using wrong type ignore codes and adding unnecessary helper
functions.

Author: cephalization

src/phoenix/server/sandbox/e2b_backend.py

@@ -45,12 +45,9 @@ def __init__(
         self._sessions: dict[str, Any] = {}
 
     def _get_sandbox_cls(self) -> Any:
-        try:
-            from e2b_code_interpreter import AsyncSandbox  # type: ignore[import-untyped]
+        from e2b_code_interpreter import AsyncSandbox  # type: ignore[import-not-found]
 
-            return AsyncSandbox
-        except ImportError:
-            raise
+        return AsyncSandbox
 
     def _create_kwargs(self) -> dict[str, Any]:
         """Build kwargs for AsyncSandbox.create().

src/phoenix/server/sandbox/wasm_backend.py

@@ -20,6 +20,8 @@
 from pathlib import Path
 from typing import Any, Optional
 
+import wasmtime  # type: ignore[import-not-found]
+
 from .types import (
     BaseNoSessionBackend,
     ExecutionResult,
@@ -38,21 +40,11 @@
 # Module-level cache: path → (engine, compiled module).
 # Engine and module must be paired — a module compiled with one engine
 # cannot be used with a store from a different engine.
-_MODULE_CACHE: dict[str, tuple[Any, Any]] = {}
-
-
-def _get_wasmtime() -> Any:
-    try:
-        import wasmtime
-
-        return wasmtime
-    except ImportError:
-        raise
+_MODULE_CACHE: dict[str, tuple[wasmtime.Engine, wasmtime.Module]] = {}
 
 
-def _get_engine_and_module(binary_path: Path) -> tuple[Any, Any]:
+def _get_engine_and_module(binary_path: Path) -> tuple[wasmtime.Engine, wasmtime.Module]:
     """Return a cached (engine, module) pair, compiling on first use."""
-    wasmtime = _get_wasmtime()
     cache_key = str(binary_path)
     if cache_key not in _MODULE_CACHE:
         engine_cfg = wasmtime.Config()
@@ -65,7 +57,6 @@ def _get_engine_and_module(binary_path: Path) -> tuple[Any, Any]:
 
 def _run_wasm(binary_path: Path, code: str, timeout: int) -> ExecutionResult:
     """Execute *code* in a wasmtime WASI context. Runs in a thread."""
-    wasmtime = _get_wasmtime()
     stdout_buf = io.StringIO()
     stderr_buf = io.StringIO()
     stdin_path: str | None = None

tests/unit/server/api/test_wasm_backend.py

@@ -113,17 +113,13 @@ class TestEngineCaching:
     """Engine and module are cached together to avoid cross-engine misuse."""
 
     def test_get_engine_and_module_caches_by_path(self) -> None:
-        from phoenix.server.sandbox.wasm_backend import (
-            _MODULE_CACHE,
-            _get_engine_and_module,
-            _get_wasmtime,
-        )
+        from phoenix.server.sandbox.wasm_backend import _MODULE_CACHE, _get_engine_and_module
 
         fake_path = Path("/fake/test-cache.wasm")
         cache_key = str(fake_path)
         _MODULE_CACHE.pop(cache_key, None)
 
-        wasmtime = _get_wasmtime()
+        import wasmtime  # type: ignore[import-not-found]
 
         with patch.object(wasmtime.Module, "from_file", return_value="fake_module"):
             engine1, mod1 = _get_engine_and_module(fake_path)
@@ -134,18 +130,14 @@ def test_get_engine_and_module_caches_by_path(self) -> None:
         _MODULE_CACHE.pop(cache_key, None)
 
     def test_different_paths_get_different_caches(self) -> None:
-        from phoenix.server.sandbox.wasm_backend import (
-            _MODULE_CACHE,
-            _get_engine_and_module,
-            _get_wasmtime,
-        )
+        from phoenix.server.sandbox.wasm_backend import _MODULE_CACHE, _get_engine_and_module
 
         path_a = Path("/fake/a.wasm")
         path_b = Path("/fake/b.wasm")
         _MODULE_CACHE.pop(str(path_a), None)
         _MODULE_CACHE.pop(str(path_b), None)
 
-        wasmtime = _get_wasmtime()
+        import wasmtime
 
         with patch.object(wasmtime.Module, "from_file", return_value="fake_module"):
             engine_a, _ = _get_engine_and_module(path_a)
@@ -166,9 +158,7 @@ def test_stdin_temp_file_is_deleted_after_run(self) -> None:
 
     def test_no_env_inherited_into_sandbox(self) -> None:
         """Verify wasi.inherit_env() is not called — user code gets no server env."""
-        from phoenix.server.sandbox.wasm_backend import _get_wasmtime
-
-        wasmtime = _get_wasmtime()
+        import wasmtime
 
         with patch.object(wasmtime.Module, "from_file"):
             with patch.object(wasmtime.WasiConfig, "inherit_env") as mock_inherit: