fix(sandbox): support move-only apply patches

src/agents/sandbox/apply_patch.py

@@ -135,6 +135,27 @@ class WorkspaceEditor:
             path=operation.path,
         )
 
+    async def _move_file(self, operation: ApplyPatchOperation) -> ApplyPatchResult:
+        if operation.move_to is None:
+            raise ApplyPatchDiffError(
+                message=f"Missing move destination for path {operation.path}",
+                path=operation.path,
+            )
+
+        relative_path, display_path = self._resolve_path(operation.path)
+        destination = self._session.normalize_path(relative_path)
+        moved_relative_path, moved_display_path = self._resolve_path(operation.move_to)
+        moved_destination = self._session.normalize_path(moved_relative_path)
+        payload = await self._read_payload(destination, op_path=operation.path)
+
+        if moved_destination != destination:
+            await self._session.mkdir(moved_destination.parent, parents=True, user=self._user)
+            data = io.StringIO(payload) if isinstance(payload, str) else io.BytesIO(payload)
+            await self._session.write(moved_destination, data, user=self._user)
+            await self._session.rm(destination, user=self._user)
+
+        return ApplyPatchResult(output=f"Moved {display_path} to {moved_display_path}")
+
     def normalize_operation(self, operation: ApplyPatchOperation) -> ApplyPatchOperation:
         """Return an operation whose paths use the workspace policy's canonical form."""
         normalized_path = self._validate_path(operation.path).as_posix()
@@ -187,6 +208,16 @@ class WorkspaceEditor:
             handle.close()
 
     async def _read_text(self, destination: Path, *, op_path: str, decode_path: Path) -> str:
+        payload = await self._read_payload(destination, op_path=op_path)
+
+        if isinstance(payload, str):
+            return payload
+        try:
+            return payload.decode("utf-8")
+        except UnicodeDecodeError as exc:
+            raise ApplyPatchDecodeError(path=decode_path, cause=exc) from exc
+
+    async def _read_payload(self, destination: Path, *, op_path: str) -> str | bytes:
         try:
             handle = await self._session.read(destination, user=self._user)
         except (FileNotFoundError, WorkspaceReadNotFoundError) as exc:
@@ -200,10 +231,7 @@ class WorkspaceEditor:
         if isinstance(payload, str):
             return payload
         if isinstance(payload, bytes | bytearray):
-            try:
-                return bytes(payload).decode("utf-8")
-            except UnicodeDecodeError as exc:
-                raise ApplyPatchDecodeError(path=decode_path, cause=exc) from exc
+            return bytes(payload)
         raise ApplyPatchDiffError(
             message=f"apply_patch read() returned non-text content: {type(payload).__name__}",
             path=op_path,

src/agents/sandbox/capabilities/tools/apply_patch_tool.py

@@ -28,7 +28,7 @@ end_patch: "*** End Patch" LF?
 hunk: add_hunk | delete_hunk | update_hunk
 add_hunk: "*** Add File: " filename LF add_line+
 delete_hunk: "*** Delete File: " filename LF
-update_hunk: "*** Update File: " filename LF change_move? change?
+update_hunk: "*** Update File: " filename LF (change_move change? | change)
 
 filename: /(.+)/
 add_line: "+" /(.*)/ LF -> line
@@ -60,7 +60,8 @@ Each operation starts with one of three headers:
 *** Update File: <path> - patch an existing file in place (optionally with a rename).
 
 May be immediately followed by *** Move to: <new path> if you want to rename the file.
-Then one or more hunks, each introduced by @@ (optionally followed by a hunk header).
+Content hunks are optional for a rename. Otherwise, include one or more hunks, each
+introduced by @@ (optionally followed by a hunk header).
 Within a hunk, each line starts with a space, -, or +.
 
 For context lines:
@@ -94,7 +95,7 @@ End := "*** End Patch" NEWLINE
 FileOp := AddFile | DeleteFile | UpdateFile
 AddFile := "*** Add File: " path NEWLINE { "+" line NEWLINE }
 DeleteFile := "*** Delete File: " path NEWLINE
-UpdateFile := "*** Update File: " path NEWLINE [ MoveTo ] { Hunk }
+UpdateFile := "*** Update File: " path NEWLINE (MoveTo { Hunk } | Hunk { Hunk })
 MoveTo := "*** Move to: " newPath NEWLINE
 Hunk := "@@" [ header ] NEWLINE { HunkLine } [ "*** End of File" NEWLINE ]
 HunkLine := (" " | "-" | "+") text NEWLINE
@@ -265,6 +266,13 @@ class SandboxApplyPatchTool(CustomTool):
             if operation.type == "create_file":
                 result = await self.editor.create_file(operation)
             elif operation.type == "update_file":
+                if operation.diff is None and operation.move_to is not None:
+                    result = await WorkspaceEditor(
+                        self.session,
+                        user=self.editor.user,
+                        workspace_scope=self.workspace_scope,
+                    )._move_file(operation)
+                else:
                     result = await self.editor.update_file(operation)
             elif operation.type == "delete_file":
                 result = await self.editor.delete_file(operation)
@@ -389,13 +397,13 @@ def _parse_update_file(lines: list[str], index: int) -> tuple[ApplyPatchOperatio
     while index < len(lines) - 1 and not _is_file_operation_header(lines[index]):
         diff_lines.append(lines[index])
         index += 1
-    if not diff_lines:
+    if not diff_lines and move_to is None:
         raise ValueError(f"Update File patch for {path} must include a hunk")
     return (
         ApplyPatchOperation(
             type="update_file",
             path=path,
-            diff=_join_diff(diff_lines),
+            diff=_join_diff(diff_lines) if diff_lines else None,
             move_to=move_to,
         ),
         index,

tests/sandbox/capabilities/test_apply_patch_tool.py

@@ -19,7 +19,11 @@ from agents.run_internal.run_steps import ToolRunCustom
 from agents.run_internal.tool_actions import CustomToolAction
 from agents.sandbox import SandboxWorkspaceScope
 from agents.sandbox.capabilities.tools import SandboxApplyPatchTool
-from agents.sandbox.errors import ApplyPatchDecodeError, ApplyPatchFileNotFoundError
+from agents.sandbox.errors import (
+    ApplyPatchDecodeError,
+    ApplyPatchDiffError,
+    ApplyPatchFileNotFoundError,
+)
 from agents.sandbox.types import User
 from agents.testing import scripted_sandbox_session
 from tests.sandbox._apply_patch_test_session import (
@@ -40,6 +44,10 @@ class TestSandboxApplyPatchTool:
         assert tool.tool_config["name"] == "apply_patch"
         assert tool.tool_config["format"]["type"] == "grammar"
         assert tool.tool_config["format"]["syntax"] == "lark"
+        assert (
+            'update_hunk: "*** Update File: " filename LF (change_move change? | change)'
+            in tool.tool_config["format"]["definition"]
+        )
 
     def test_converter_uses_sandbox_custom_apply_patch_tool_config(self) -> None:
         tool = SandboxApplyPatchTool(session=scripted_sandbox_session())
@@ -221,6 +229,22 @@ class TestSandboxApplyPatchTool:
         assert isinstance(result, ToolCallOutputItem)
         assert "apply_patch input must start with '*** Begin Patch'" in result.output
 
+    @pytest.mark.asyncio
+    async def test_empty_update_surfaces_tool_error_without_modifying_file(self) -> None:
+        session = ApplyPatchSession()
+        session.files[Path("/workspace/notes.txt")] = b"hello\n"
+        tool = SandboxApplyPatchTool(session=session)
+
+        result = await _execute_custom_tool_call(
+            tool,
+            context_wrapper=make_context_wrapper(),
+            raw_input=("*** Begin Patch\n*** Update File: notes.txt\n*** End Patch\n"),
+        )
+
+        assert isinstance(result, ToolCallOutputItem)
+        assert "Update File patch for notes.txt must include a hunk" in result.output
+        assert session.files[Path("/workspace/notes.txt")] == b"hello\n"
+
     @pytest.mark.asyncio
     async def test_editor_create_update_delete_round_trip(self) -> None:
         session = ApplyPatchSession()
@@ -558,6 +582,27 @@ class TestSandboxApplyPatchTool:
         assert session.rm_users == []
         assert session.files[Path("/workspace/existing.txt")] == b"new\n"
 
+    @pytest.mark.asyncio
+    async def test_editor_rejects_move_without_diff_before_filesystem_access(self) -> None:
+        session = ApplyPatchSession()
+        session.files[Path("/workspace/existing.txt")] = b"old\n"
+        tool = SandboxApplyPatchTool(session=session)
+
+        with pytest.raises(ApplyPatchDiffError, match="Missing diff"):
+            await cast(
+                Awaitable[ApplyPatchResult],
+                tool.editor.update_file(
+                    ApplyPatchOperation(
+                        type="update_file",
+                        path="existing.txt",
+                        diff=None,
+                        move_to="moved.txt",
+                    )
+                ),
+            )
+
+        assert session.files == {Path("/workspace/existing.txt"): b"old\n"}
+
     @pytest.mark.asyncio
     async def test_custom_tool_input_create_update_move_delete(self) -> None:
         session = ApplyPatchSession()
@@ -600,6 +645,28 @@ class TestSandboxApplyPatchTool:
         )
         assert Path("/workspace/moved.txt") not in session.files
 
+    @pytest.mark.asyncio
+    async def test_custom_tool_input_moves_file_without_content_hunk(self) -> None:
+        session = ApplyPatchSession()
+        original = b"\xffhello\r\nworld\n"
+        session.files[Path("/workspace/notes.txt")] = original
+        tool = SandboxApplyPatchTool(session=session)
+
+        result = await _execute_custom_tool_call(
+            tool,
+            context_wrapper=make_context_wrapper(),
+            raw_input=(
+                "*** Begin Patch\n"
+                "*** Update File: notes.txt\n"
+                "*** Move to: moved.txt\n"
+                "*** End Patch\n"
+            ),
+        )
+
+        assert result.output == "Moved notes.txt to moved.txt"
+        assert Path("/workspace/notes.txt") not in session.files
+        assert session.files[Path("/workspace/moved.txt")] == original
+
 
 async def _execute_custom_tool_call(
     tool: SandboxApplyPatchTool,