refactor(config): add set_config_value for non-merge replacement

src/presa_mano/config.py

@@ -63,6 +63,36 @@ def update_config(patch: dict[str, Any]) -> dict[str, Any]:
         return deepcopy(merged)
 
 
+def set_config_value(path: list[str], value: Any) -> dict[str, Any]:
+    """Set a value at a nested path in config, REPLACING the existing value
+    (unlike update_config which deep-merges). Useful when you need to wholesale
+    replace a dict (e.g., to remove keys not present in the new value).
+
+    Example:
+        set_config_value(["pose_3d", "named_poses"], {"a": {...}, "b": {...}})
+
+    Walks the path creating intermediate dicts if missing. Persists to disk.
+    Returns the new full config (deep-copied)."""
+    if not path:
+        raise ValueError("path must be a non-empty list of keys")
+    with _LOCK:
+        if _STATE["config"] is None:
+            load_config()
+        cfg = _STATE["config"]
+        node = cfg
+        for key in path[:-1]:
+            child = node.get(key)
+            if not isinstance(child, dict):
+                child = {}
+                node[key] = child
+            node = child
+        node[path[-1]] = value
+        if _STATE["path"]:
+            with open(_STATE["path"], "w") as f:
+                yaml.safe_dump(cfg, f, sort_keys=False)
+        return deepcopy(cfg)
+
+
 def _deep_merge(base: dict[str, Any], patch: dict[str, Any]) -> dict[str, Any]:
     out = deepcopy(base)
     for k, v in patch.items():