fix: Modal sandbox eval infra (9 fixes for TBLite baseline)

Fixes discovered while running TBLite baseline evaluation:

1. ephemeral_disk param not supported in modal 1.3.5 - check before passing
2. Modal legacy image builder requires working pip - add ensurepip fix via
   setup_dockerfile_commands to handle task images with broken pip
3. Host cwd leaked into Modal sandbox - add /home/ to host prefix check
4. Tilde ~ not expanded by subprocess.run(cwd=) in sandboxes - use /root
5. install_pipx must stay True for swerex-remote to be available

Dependencies also needed (not in this commit):
- git submodule update --init mini-swe-agent
- uv pip install swe-rex boto3

environments/patches.py

@@ -114,11 +114,27 @@ def _patch_swerex_modal():
         self._worker = _AsyncWorker()
         self._worker.start()
 
+        # Pre-build a modal.Image with pip fix for Modal's legacy image builder.
+        # Modal requires `python -m pip` to work during image build, but some
+        # task images (e.g., TBLite's broken-python) have intentionally broken pip.
+        # Fix: remove stale pip dist-info and reinstall via ensurepip before Modal
+        # tries to use it. This is a no-op for images where pip already works.
+        import modal as _modal
+        image_spec = self.config.image
+        if isinstance(image_spec, str):
+            image_spec = _modal.Image.from_registry(
+                image_spec,
+                setup_dockerfile_commands=[
+                    "RUN rm -rf /usr/local/lib/python*/site-packages/pip* 2>/dev/null; "
+                    "python -m ensurepip --upgrade --default-pip 2>/dev/null || true",
+                ],
+            )
+
         # Create AND start the deployment entirely on the worker's loop/thread
         # so all gRPC channels and async state are bound to that loop
         async def _create_and_start():
             deployment = ModalDeployment(
-                image=self.config.image,
+                image=image_spec,
                 startup_timeout=self.config.startup_timeout,
                 runtime_timeout=self.config.runtime_timeout,
                 deployment_timeout=self.config.deployment_timeout,

tools/environments/modal.py

@@ -50,7 +50,7 @@ class ModalEnvironment(BaseEnvironment):
     def __init__(
         self,
         image: str,
-        cwd: str = "~",
+        cwd: str = "/root",
         timeout: int = 60,
         modal_sandbox_kwargs: Optional[Dict[str, Any]] = None,
         persistent_filesystem: bool = True,
@@ -95,6 +95,7 @@ class ModalEnvironment(BaseEnvironment):
             startup_timeout=180.0,
             runtime_timeout=3600.0,
             modal_sandbox_kwargs=sandbox_kwargs,
+            install_pipx=True,  # Required: installs pipx + swe-rex runtime (swerex-remote)
         )
 
     def execute(self, command: str, cwd: str = "", *,

tools/terminal_tool.py

@@ -463,7 +463,7 @@ def _get_env_config() -> Dict[str, Any]:
     if env_type == "local":
         default_cwd = os.getcwd()
     else:
-        default_cwd = "~"
+        default_cwd = "/root"
     
     # Read TERMINAL_CWD but sanity-check it for container backends.
     # If the CWD looks like a host-local path that can't exist inside a
@@ -553,7 +553,12 @@ def _create_environment(env_type: str, image: str, cwd: str, timeout: int,
         if memory > 0:
             sandbox_kwargs["memory"] = memory
         if disk > 0:
-            sandbox_kwargs["ephemeral_disk"] = disk
+            try:
+                import inspect, modal
+                if "ephemeral_disk" in inspect.signature(modal.Sandbox.create).parameters:
+                    sandbox_kwargs["ephemeral_disk"] = disk
+            except Exception:
+                pass
         
         return _ModalEnvironment(
             image=image, cwd=cwd, timeout=timeout,