done

libs/cli/langgraph_cli/engine_runtime_mode.py

@@ -0,0 +1,69 @@
+"""Resolve the LangGraph engine runtime mode."""
+
+import json
+import pathlib
+
+import click
+
+_DISTRIBUTED_MIN_VERSION = (0, 7, 68)
+
+
+def resolve_engine_runtime_mode(
+    config_path: pathlib.Path,
+    api_version: str,
+    engine_runtime_mode_cli_param: str | None,
+) -> str:
+    """Resolve the engine runtime mode.
+
+    *api_version* must already be resolved to a patch-level semver string.
+
+    Returns ``"distributed"`` or ``"combined_queue_worker"``.
+
+    Raises `click.ClickException` when distributed mode is requested but
+    not supported (JavaScript project or api_version <= 0.7.67).
+    """
+    requires_combined = _requires_combined(config_path, api_version)
+
+    if engine_runtime_mode_cli_param == "distributed":
+        if requires_combined:
+            reasons = _constraint_reasons(config_path, api_version)
+            raise click.ClickException(
+                f"Distributed runtime is not supported for {' and '.join(reasons)}."
+            )
+        return "distributed"
+
+    if engine_runtime_mode_cli_param == "combined_queue_worker":
+        return "combined_queue_worker"
+
+    # No explicit choice → default to distributed
+    return "distributed"
+
+
+def _requires_combined(config_path: pathlib.Path, api_version: str) -> bool:
+    return _is_javascript_project(config_path) or _version_too_old(api_version)
+
+
+def _version_too_old(api_version: str) -> bool:
+    try:
+        parts = tuple(int(x) for x in api_version.split("."))
+    except (ValueError, AttributeError):
+        return True
+    return parts < _DISTRIBUTED_MIN_VERSION
+
+
+def _is_javascript_project(config_path: pathlib.Path) -> bool:
+    try:
+        with open(config_path) as f:
+            cfg = json.load(f)
+    except (OSError, json.JSONDecodeError):
+        return False
+    return bool(cfg.get("node_version")) and not cfg.get("python_version")
+
+
+def _constraint_reasons(config_path: pathlib.Path, api_version: str) -> list[str]:
+    reasons: list[str] = []
+    if _is_javascript_project(config_path):
+        reasons.append("JavaScript projects")
+    if _version_too_old(api_version):
+        reasons.append(f"API version {api_version} (<= 0.7.67)")
+    return reasons