Implement write support for expression, textTemplate, and selection pluggable widget property types in mxcli exec #1585

mxcli version: v0.26.0 (2026-10-11)
Mendix version: 11.12.4

Context:
mxcli widget describe correctly discovers all pluggable widget properties from the .mpk and reports their type. The MDL parser accepts them without errors.
However, mxcli exec does not persist all property types equally — some are silently dropped at write time.

What mxcli exec currently persists correctly:

┌──────────────────────┬─────────────────────────────────────┬───────────┐
│ Type │ Example │ Persisted │
├──────────────────────┼─────────────────────────────────────┼───────────┤
│ boolean │ Mode: true │ ✅ │
├──────────────────────┼─────────────────────────────────────┼───────────┤
│ enumeration │ FilterType: 'startsWith' │ ✅ │
├──────────────────────┼─────────────────────────────────────┼───────────┤
│ attribute │ AttributeToSearch: NId │ ✅ │
├──────────────────────┼─────────────────────────────────────┼───────────┤
│ datasource │ EntityDatasource: database from ... │ ✅ │
├──────────────────────┼─────────────────────────────────────┼───────────┤
│ action │ OnChange: call nanoflow ... │ ✅ │
├──────────────────────┼─────────────────────────────────────┼───────────┤
│ widgets (child slot) │ CustomContent { ... } │ ✅ │
└──────────────────────┴─────────────────────────────────────┴───────────┘

What mxcli exec does NOT persist:

┌──────────────┬───────────────────────────────────────┬───────────┐
│ Type │ Example │ Persisted │
├──────────────┼───────────────────────────────────────┼───────────┤
│ expression │ Placeholder: $currentObject/NId │ ❌ │
├──────────────┼───────────────────────────────────────┼───────────┤
│ expression │ SelectedObject: $currentObject/Id │ ❌ │
├──────────────┼───────────────────────────────────────┼───────────┤
│ textTemplate │ RequiredValidationMessage: 'Required' │ ❌ │
├──────────────┼───────────────────────────────────────┼───────────┤
│ selection │ selectionApi: MySelectionName │ ❌ │
└──────────────┴───────────────────────────────────────┴───────────┘

Observed behaviour:
The MDL parser accepts the properties without errors. During exec, the values are silently dropped with a warning. After exec, DESCRIBE PAGE does not include
them — as if they were never written. The model is left in a partial state with no indication of what is missing beyond the warning emitted at exec time.

Minimal reproduction:
mdl
mdl 1;
create or modify page MyModule.MyPage (
Layout: MyModule.MyLayout,
Params: ( $Obj: MyModule.MyEntity )
) {
dataview dv (DataSource: $Obj) {
pluggablewidget myWidget (
SomeExpressionProperty: $currentObject/MyAttribute,
SomeTextTemplate: 'This field is required',
SomeSelectionProperty: MySelectionName
)
}
};
Expected: all three properties written to the .mpr and visible in DESCRIBE PAGE.

Actual: a warning is emitted for each, all three values are dropped.

Impact:
step after exec, breaking the fully-automated pipeline and introducing a human error surface that scales with the number of pages migrated. There is currently
no way to detect which properties were silently dropped without re-opening every page in Studio Pro.

Request:
Implement persistence of expression, textTemplate, and selection pluggable widget property types in exec, consistent with how boolean, enumeration, attribute,
datasource, and action are already handled.