fix(cli): add buildkit syntax directiive, update tests (#6385)

**Description:** Adds the syntax directive to generated dockerfile for
langgraph builds if we have additional contexts
**Issue:** fixes issue with python monorepo builds failing
**Dependencies:** N/A

libs/cli/langgraph_cli/__init__.py

@@ -1 +1 @@
-__version__ = "0.4.5"
+__version__ = "0.4.6"

libs/cli/langgraph_cli/config.py

@@ -926,35 +926,51 @@ ADD {relpath} /deps/{name}
             ]
         )
     image_str = docker_tag(config, base_image, api_version)
-    docker_file_contents = [
-        f"FROM {image_str}",
-        "",
-        os.linesep.join(config["dockerfile_lines"]),
-        "",
-        installs,
-        "",
-        "# -- Installing all local dependencies --",
-        f"""RUN for dep in /deps/*; do \
+
+    # Prepare docker file contents
+    docker_file_contents = []
+
+    # Add syntax directive if we have additional contexts (requires BuildKit frontend.contexts capability)
+    if local_deps.additional_contexts:
+        docker_file_contents.extend(
+            [
+                "# syntax=docker/dockerfile:1.4",
+                "",
+            ]
+        )
+
+    # Add main dockerfile content
+    docker_file_contents.extend(
+        [
+            f"FROM {image_str}",
+            "",
+            os.linesep.join(config["dockerfile_lines"]),
+            "",
+            installs,
+            "",
+            "# -- Installing all local dependencies --",
+            f"""RUN for dep in /deps/*; do \
             echo "Installing $dep"; \
             if [ -d "$dep" ]; then \
                 echo "Installing $dep"; \
                 (cd "$dep" && {global_reqs_pip_install} -e .); \
             fi; \
         done""",
-        "# -- End of local dependencies install --",
-        os.linesep.join(env_vars),
-        "",
-        js_inst_str,
-        "",
-        # Add pip cleanup after all installations are complete
-        _get_pip_cleanup_lines(
-            install_cmd=install_cmd,
-            to_uninstall=build_tools_to_uninstall,
-            pip_installer=pip_installer,
-        ),
-        "",
-        f"WORKDIR {local_deps.working_dir}" if local_deps.working_dir else "",
-    ]
+            "# -- End of local dependencies install --",
+            os.linesep.join(env_vars),
+            "",
+            js_inst_str,
+            "",
+            # Add pip cleanup after all installations are complete
+            _get_pip_cleanup_lines(
+                install_cmd=install_cmd,
+                to_uninstall=build_tools_to_uninstall,
+                pip_installer=pip_installer,
+            ),
+            "",
+            f"WORKDIR {local_deps.working_dir}" if local_deps.working_dir else "",
+        ]
+    )
 
     additional_contexts: dict[str, str] = {}
     for p in local_deps.additional_contexts:

libs/cli/tests/unit_tests/cli/test_cli.py

@@ -141,6 +141,7 @@ services:
             additional_contexts:
                 - cli_1: {str(pathlib.Path(__file__).parent.parent.parent.parent.absolute())}
             dockerfile_inline: |
+                # syntax=docker/dockerfile:1.4
                 FROM langchain/langgraph-api:3.11
                 # -- Adding local package . --
                 ADD . /deps/cli

libs/cli/tests/unit_tests/test_config.py

@@ -419,6 +419,7 @@ def test_config_to_docker_simple():
         "langchain/langgraph-api",
     )
     expected_docker_stdin = f"""\
+# syntax=docker/dockerfile:1.4
 FROM langchain/langgraph-api:3.11
 # -- Installing local requirements --
 COPY --from=outer-requirements.txt requirements.txt /deps/outer-graphs_reqs_a/graphs_reqs_a/requirements.txt
@@ -482,6 +483,7 @@ def test_config_to_docker_outside_path():
     )
     expected_docker_stdin = (
         """\
+# syntax=docker/dockerfile:1.4
 FROM langchain/langgraph-api:3.11
 # -- Adding non-package dependency unit_tests --
 ADD . /deps/outer-unit_tests/unit_tests