Expose unified synthesis mode via the CLI

The CLI (python llama_stack_configuration.py -c config.yaml) only
called generate_configuration(), the legacy enrichment mode that
requires an already-built run.yaml as input. There was no CLI path
to synthesize_configuration()/synthesize_to_file(), the unified mode
that builds run.yaml from lightspeed-stack.yaml alone, so consumers
of unified mode had to import the module instead of using the
documented script interface.

Add a --synthesize flag: when set, the CLI builds the config via
synthesize_to_file() from -c alone (ignoring -i), instead of enriching
an existing run.yaml. An empty or comment-only -c file now loads as
{} rather than None, so it doesn't crash synthesize_to_file() with an
opaque AttributeError.

Author: omkarjoshi0304

src/llama_stack_configuration.py

@@ -1481,7 +1481,7 @@ def generate_configuration(
 def main() -> None:
     """CLI entry point."""
     parser = ArgumentParser(
-        description="Enrich Llama Stack config with Lightspeed values",
+        description="Enrich or synthesize Llama Stack config from Lightspeed values",
     )
     parser.add_argument(
         "-c",
@@ -1493,20 +1493,32 @@ def main() -> None:
         "-i",
         "--input",
         default="run.yaml",
-        help="Input Llama Stack config (default: run.yaml)",
+        help="Input Llama Stack config for legacy enrichment mode; ignored "
+        "with --synthesize (default: run.yaml)",
     )
     parser.add_argument(
         "-o",
         "--output",
         default="run_.yaml",
-        help="Output enriched config (default: run_.yaml)",
+        help="Output config file (default: run_.yaml)",
+    )
+    parser.add_argument(
+        "--synthesize",
+        action="store_true",
+        help="Build a complete run.yaml from -c alone instead of enriching "
+        "an existing run.yaml given by -i",
     )
     args = parser.parse_args()
 
     with open(args.config, "r", encoding="utf-8") as f:
-        config = yaml.safe_load(f)
+        config = yaml.safe_load(f) or {}
 
-    generate_configuration(args.input, args.output, config)
+    if args.synthesize:
+        synthesize_to_file(
+            config, args.output, config_file_dir=str(Path(args.config).parent)
+        )
+    else:
+        generate_configuration(args.input, args.output, config)
 
 
 if __name__ == "__main__":

tests/unit/test_llama_stack_synthesize.py

@@ -6,8 +6,11 @@
 write-to-file step (persistent path, mode 0600).
 """
 
+# pylint: disable=too-many-lines
+
 import os
 import stat
+import sys
 from pathlib import Path
 from typing import Any, Optional, get_args
 
@@ -20,6 +23,7 @@
     deep_merge_list_replace,
     ensure_mcp_tool_runtime,
     load_default_baseline,
+    main,
     migrate_config_dumb,
     synthesize_configuration,
     synthesize_to_file,
@@ -915,6 +919,103 @@ def test_migrate_config_dumb_rejects_non_mapping_inputs(tmp_path: Path) -> None:
         migrate_config_dumb(str(empty_run), lcs_path, out_path)
 
 
+# ---------------------------------------------------------------------------
+# CLI entry point
+# ---------------------------------------------------------------------------
+
+
+def test_main_synthesize_flag_builds_run_yaml(
+    tmp_path: Path, monkeypatch: pytest.MonkeyPatch
+) -> None:
+    """--synthesize builds a complete run.yaml from -c alone."""
+    config_path = tmp_path / "lightspeed-stack.yaml"
+    config_path.write_text(
+        yaml.dump(
+            {
+                "llama_stack": {
+                    "config": {
+                        "baseline": "empty",
+                        "native_override": {"version": 2, "apis": ["inference"]},
+                    }
+                }
+            }
+        ),
+        encoding="utf-8",
+    )
+    output_path = tmp_path / "run.yaml"
+
+    monkeypatch.setattr(
+        sys,
+        "argv",
+        [
+            "llama_stack_configuration.py",
+            "-c",
+            str(config_path),
+            "-o",
+            str(output_path),
+            "--synthesize",
+        ],
+    )
+    main()
+
+    result = yaml.safe_load(output_path.read_text(encoding="utf-8"))
+    assert result == {"version": 2, "apis": ["inference"]}
+
+
+def test_main_default_uses_legacy_enrichment(
+    tmp_path: Path, monkeypatch: pytest.MonkeyPatch
+) -> None:
+    """Without --synthesize, the CLI keeps calling legacy generate_configuration."""
+    config_path = tmp_path / "lightspeed-stack.yaml"
+    config_path.write_text(yaml.dump({}), encoding="utf-8")
+    input_path = tmp_path / "run.yaml"
+    input_path.write_text(yaml.dump({"version": 2}), encoding="utf-8")
+    output_path = tmp_path / "run_.yaml"
+
+    monkeypatch.setattr(
+        sys,
+        "argv",
+        [
+            "llama_stack_configuration.py",
+            "-c",
+            str(config_path),
+            "-i",
+            str(input_path),
+            "-o",
+            str(output_path),
+        ],
+    )
+    main()
+
+    result = yaml.safe_load(output_path.read_text(encoding="utf-8"))
+    assert result["version"] == 2
+
+
+def test_main_synthesize_flag_handles_empty_config_file(
+    tmp_path: Path, monkeypatch: pytest.MonkeyPatch
+) -> None:
+    """An empty/comment-only -c file loads as {} instead of crashing on None."""
+    config_path = tmp_path / "lightspeed-stack.yaml"
+    config_path.write_text("# only a comment\n", encoding="utf-8")
+    output_path = tmp_path / "run.yaml"
+
+    monkeypatch.setattr(
+        sys,
+        "argv",
+        [
+            "llama_stack_configuration.py",
+            "-c",
+            str(config_path),
+            "-o",
+            str(output_path),
+            "--synthesize",
+        ],
+    )
+    main()
+
+    assert output_path.exists()
+
+
 # ---------------------------------------------------------------------------
 # reference profiles (LCORE-2346)
 # ---------------------------------------------------------------------------