function Set-PersonaConditionLeaf {
    <#
    .SYNOPSIS
        Replaces a leaf condition's fields in place (FR-028).

    .DESCRIPTION
        Every condition-specific field (`property`, `value`, `values`,
        `groupObjectIds`, `roleIds`, `membershipMode`) is cleared before Fields is
        applied, then only the keys in Fields are set. This is not tidiness - the
        schema's `additionalProperties: false` on `condition` (VR-001 layer 2) rejects
        a stray field outright, and switching, say, a condition from `equals` (which
        carries `value`) to `in` (which carries `values`) would otherwise leave the
        old `value` behind and fail schema validation for a reason the editor caused
        but did not explain.

        `type` and `operator` are cleared and reset the same way, since a caller
        editing a condition typically passes both.

    .PARAMETER Node
        The leaf condition to edit (from Get-PersonaConditionNode). Mutated in place.

    .PARAMETER Fields
        The complete replacement field set for this leaf, for example:
        `@{ type = 'property'; property = 'Department'; operator = 'isNotNull' }`.

    .OUTPUTS
        System.Object - the same Node, mutated in place, returned for convenience.
    #>
    [CmdletBinding()]
    [OutputType([object])]
    param(
        [Parameter(Mandatory)]
        [object] $Node,

        [Parameter(Mandatory)]
        [hashtable] $Fields
    )

    if ($null -ne $Node.PSObject.Properties['conditions']) {
        throw 'The target node is a condition group, not a leaf condition.'
    }

    $knownFields = @('type', 'property', 'operator', 'value', 'values', 'groupObjectIds', 'roleIds', 'membershipMode', 'caseSensitive')

    foreach ($key in $knownFields) {
        if ($null -ne $Node.PSObject.Properties[$key]) {
            $Node.PSObject.Properties.Remove($key)
        }
    }

    foreach ($entry in $Fields.GetEnumerator()) {
        $Node | Add-Member -NotePropertyName $entry.Key -NotePropertyValue $entry.Value -Force
    }

    $Node
}