Documented how JSON types get their generated contracts

app/AGENTS.md

@@ -34,6 +34,7 @@ Key structure:
 - **New files and folders in the data or configuration directory** - Whoever adds a file or folder directly to the data or configuration directory, or below `plugins/` or `databases/` one which needs a decision of its own, lists it in `DataBackupContents.ENTRIES`: as part of a backup, or with the reason a backup leaves it out. A backup takes along only what is listed as included, and a restore replaces only that. An entry included in a backup also goes into `REPLACEABLE_ELEMENTS` in `runtime/src/data_restore.rs`; otherwise the runtime refuses to restore it. The folder panel on the information page shows the list to users who back up these folders with a tool of their own.
 - **Sending content on** - Content which leaves one place for another, such as the result of an assistant sent to another assistant or a text sent into the chat, travels as a `TextLaunchPayload` through `AssistantLaunchService`, together with the restrictions of where it was written (`ChatRestrictions`, see `ChatThread.CaptureRestrictions`). Never hand over a bare string: the destination would let any provider or tool see content which its source kept from them. Build the payload with `AssistantLaunchService.CreateTextPayloadAsync`, which filters what an AI wrote for prompt injections before it reaches the next model as a message of the user. An assistant which allows sending to it overrides `AssistantBase.ApplyTextLaunchPayload`, and `SendToReceiverTests` checks that every one does; the restrictions themselves are applied centrally in `AssistantBase`.
 - **JSON in model answers** - Read the JSON part of a model answer with `ModelAnswerJson`, never with a scanner of your own. It skips the prose and code fences around the JSON but checks nothing, so broken JSON reaches the deserializer unchanged and its message can go back to the model.
+- **JSON contracts** - The contracts of all JSON which AI Studio reads or writes are generated while compiling. Each kind of options names the `JsonSerializerContext` which knows its types, with `GenerationMode = Metadata`, as its `TypeInfoResolver` and ends with `.AsReadOnly()`; only `VisualBriefingJson.Canonical` leaves that out, see MWAIS0010. A new JSON type goes into the context of the options it is read or written with, and into `JsonTestRoots` in `app/Tests/Serialization/`, whose contract, defaults, and coverage tests then check it. Give JSON types `set` instead of `init`, because the source generator of .NET 10 drops the initializer of an `init` property which the JSON leaves out, and write a record or a `JsonObject` instead of an anonymous type. Never call System.Text.Json without options, nor with `JsonSerializerOptions.Default`, `.Web`, or a `DefaultJsonTypeInfoResolver`: each of them builds the contracts by reflection, whose code a published build may lack. MWAIS0015 refuses them while compiling, `JsonOptionsResolverTests` checks the resolvers of all options of the app, and the trim smoke test of `dotnet run verify` builds the contract of every type of their contexts in a trimmed build. Reflection itself stays switched on, because Blazor Server needs it for JSON of its own, see `Trimming.props`.
 - **Long menus** - MudBlazor keeps a `MudSelect` inside the window by itself, but never a `MudMenu`: a menu taller than the window runs past its edge, and its lower entries cannot be reached. Give every `MudMenu` whose entries come from data, such as the assistants or the profiles, `MaxHeight="@MenuDefaults.MAX_HEIGHT"`, so that it scrolls.
 - **Growing popovers** - Since version 9, MudBlazor places an open popover again whenever its content changes size. Content which unfolds later, such as a `MudCollapse` or an `ExpansionPanel` inside a `MudPopover`, therefore stays inside the window and needs no code of its own.
 - **Encryption** - Initialized before Rust service is marked ready

app/Trimming.props

@@ -10,7 +10,7 @@
         <TrimmerRemoveSymbols>true</TrimmerRemoveSymbols> <!-- Remove debug symbols -->
         <EnableUnsafeBinaryFormatterSerialization>false</EnableUnsafeBinaryFormatterSerialization> <!-- Remove unsafe binary formatter serialization -->
         <EnableUnsafeUTF7Encoding>false</EnableUnsafeUTF7Encoding> <!-- Remove unsafe UTF7 encoding -->
-        <JsonSerializerIsReflectionEnabledByDefault>true</JsonSerializerIsReflectionEnabledByDefault> <!-- Enable reflection for JSON serialization -->
+        <JsonSerializerIsReflectionEnabledByDefault>true</JsonSerializerIsReflectionEnabledByDefault> <!-- Blazor Server needs reflection for JSON of its own, while the options of AI Studio use generated contracts only. Without this line, PublishTrimmed switches reflection off, even for dotnet run -->
         <SuppressTrimAnalysisWarnings>true</SuppressTrimAnalysisWarnings> <!-- Suppress trim analysis warnings -->
     </PropertyGroup>