SaveState/LoadState discards command metadata: timestamps reset to load time, ChangeSize to 1, CustomData lost

[matt-edmondson]

What's wrong

JsonUndoRedoSerializer serializes each command's Metadata. On load, though, PlaceholderCommand (UndoRedo/Services/JsonUndoRedoSerializer.cs:~186) passes only ChangeType and AffectedItems to the BaseCommand constructor, which builds a fresh ChangeMetadata with:

• DateTimeOffset.Now,
• a size of 1,
• no CustomData.

The deserialized metadata is thrown away, although the comment at around line 104 says the placeholder "preserves metadata".

Failure scenario (reproduced with a temporary MSTest)

Execute DelegateCommand(..., size: 42), then SaveStateAsync, then LoadStateAsync into a new service:

orig   size=42 ts=...54.3085987
loaded size=1  ts=...54.4617403

After a reload, any history or change-visualization UI (GetChangeVisualizations) shows every change as having happened at load time with size 1, and any CustomData the app attached is gone.

Suggested fix

BaseCommand.Metadata is virtual with a protected setter. In PlaceholderCommand's constructor, assign the deserialized ChangeMetadata: Metadata = metadata;. Or override Metadata to return it.

Acceptance: a round-trip test asserting that Timestamp, ChangeSize and CustomData survive save and load.