fix(workspace-changes): keep the package importable as a first import (#6602) (#6608)

`workspace_changes/api.py` imports `deerflow.runtime.user_context` for the
AUTO sentinel (#6282). Importing that submodule runs the runtime package init,
which imports `.runs` -> `worker` -> `deerflow.workspace_changes` back for
`capture_workspace_snapshot` and friends, so importing `.api` as the package's
first statement failed with ImportError while those names were still unbound.

Resolve the re-export lazily via a module-level `__getattr__`, the pattern
`deerflow/subagents/__init__.py` already uses.

backend/packages/harness/deerflow/workspace_changes/__init__.py

@@ -1,4 +1,3 @@
-from .api import get_workspace_changes_response
 from .diff import compare_snapshots, get_changed_output_paths, get_changed_paths
 from .recorder import capture_workspace_snapshot, record_workspace_changes
 from .scanner import scan_workspace_roots
@@ -32,3 +31,17 @@ __all__ = [
     "record_workspace_changes",
     "scan_workspace_roots",
 ]
+
+
+def __getattr__(name: str):
+    # `.api` reads `deerflow.runtime.user_context` for the AUTO sentinel, and
+    # importing that package runs `deerflow.runtime`'s init, which imports
+    # `.runs` -> `worker` -> this package. Resolving it lazily keeps this
+    # package importable as a process's first import instead of failing with
+    # ImportError while its own names are still unbound.
+    if name == "get_workspace_changes_response":
+        from .api import get_workspace_changes_response
+
+        globals()[name] = get_workspace_changes_response
+        return get_workspace_changes_response
+    raise AttributeError(f"module {__name__!r} has no attribute {name!r}")

backend/tests/test_gateway_imports.py

@@ -72,3 +72,27 @@ def test_subagent_package_public_executor_exports_are_lazy_importable() -> None:
     )
     assert result.returncode == 0, result.stderr
     assert "SubagentExecutor SubagentResult" in result.stdout
+
+
+def test_workspace_changes_package_imports_standalone() -> None:
+    """The workspace-changes package must import as the process's first import.
+
+    ``workspace_changes.api`` reads ``deerflow.runtime.user_context`` for the
+    ``AUTO`` sentinel, which runs ``deerflow.runtime``'s package init and imports
+    ``.runs`` -> ``worker`` -> ``deerflow.workspace_changes`` again. Importing
+    ``.api`` before this package bound its own names made that re-entrant import
+    fail with ImportError whenever ``deerflow.runtime`` had not been imported
+    yet.
+    """
+    result = subprocess.run(
+        [
+            sys.executable,
+            "-c",
+            "import deerflow.workspace_changes as w; print(w.scan_workspace_roots.__name__, w.get_workspace_changes_response.__name__)",
+        ],
+        capture_output=True,
+        text=True,
+        env=_gateway_import_env(),
+    )
+    assert result.returncode == 0, result.stderr
+    assert "scan_workspace_roots get_workspace_changes_response" in result.stdout