feat(tools): yaml writer with ruamel (preserves comments, atomic + backup)

Uses ruamel.yaml so existing comments / formatting in commands.yaml
survive a save. Each write creates commands.yaml.bak first, then
atomically renames a .tmp file into place. Tests cover round-trip for
all action types plus comment-preservation on append.

tools/command_builder/yaml_writer.py

@@ -0,0 +1,91 @@
+from __future__ import annotations
+
+import io
+import os
+import shutil
+from pathlib import Path
+from typing import Optional
+
+from ruamel.yaml import YAML
+
+from .schema import CommandEntry, SchemaError, command_from_dict
+
+
+DEFAULT_YAML_PATH = Path("C:/Jarvis/python/commands.yaml")
+
+
+def _make_yaml() -> YAML:
+    y = YAML()
+    y.preserve_quotes = True
+    y.indent(mapping=2, sequence=4, offset=2)
+    y.width = 4096
+    return y
+
+
+def load_yaml(path: Path = DEFAULT_YAML_PATH):
+    y = _make_yaml()
+    with open(path, "rt", encoding="utf-8") as f:
+        return y.load(f) or {}
+
+
+def list_command_ids(path: Path = DEFAULT_YAML_PATH) -> list:
+    try:
+        data = load_yaml(path)
+    except FileNotFoundError:
+        return []
+    return list(data.keys())
+
+
+def _dump_to_string(data) -> str:
+    y = _make_yaml()
+    buf = io.StringIO()
+    y.dump(data, buf)
+    return buf.getvalue()
+
+
+def _atomic_write(path: Path, text: str) -> None:
+    tmp = path.with_suffix(path.suffix + ".tmp")
+    with open(tmp, "wt", encoding="utf-8", newline="\n") as f:
+        f.write(text)
+    os.replace(tmp, path)
+
+
+def _backup(path: Path) -> Optional[Path]:
+    if not path.exists():
+        return None
+    bak = path.with_suffix(path.suffix + ".bak")
+    shutil.copy2(path, bak)
+    return bak
+
+
+def append_command(entry: CommandEntry, path: Path = DEFAULT_YAML_PATH) -> None:
+    try:
+        data = load_yaml(path)
+    except FileNotFoundError:
+        data = {}
+    if entry.cmd_id in data:
+        raise SchemaError(f"command id already exists: {entry.cmd_id}")
+    data[entry.cmd_id] = entry.to_dict()
+    _backup(path)
+    text = _dump_to_string(data)
+    _atomic_write(path, text)
+
+
+def upsert_command(entry: CommandEntry, path: Path = DEFAULT_YAML_PATH) -> None:
+    try:
+        data = load_yaml(path)
+    except FileNotFoundError:
+        data = {}
+    data[entry.cmd_id] = entry.to_dict()
+    _backup(path)
+    text = _dump_to_string(data)
+    _atomic_write(path, text)
+
+
+def validate_file(path: Path = DEFAULT_YAML_PATH) -> list:
+    data = load_yaml(path)
+    out = []
+    for cmd_id, body in data.items():
+        plain_body = body
+        out.append(command_from_dict(cmd_id, dict(plain_body)))
+    return out