Runic.Application 0.7.0-preview.6

Runic.Application

Typed .NET Windows and Views with generated TypeScript clients. C# ViewModels own application state, commands, and operation lifetimes; a React, Vue, Svelte, Angular, or plain TypeScript frontend renders them through a generated client. The package's types are in the Runic.Application.Views namespace.

Install

Reference a host adapter; it brings this package and its build targets:

dotnet add package Runic.Application.CsWebUi --prerelease   # CS-WebUI browser or WebView window
dotnet add package Runic.Application.Desktop --prerelease   # or: Runic Desktop native host
dotnet add package CommunityToolkit.Mvvm                     # or ReactiveUI with Runic.Application.ReactiveUI
dotnet add package Microsoft.Extensions.DependencyInjection  # ServiceCollection; the adapters need only the abstractions

To start a new application, run the guided creator (dnx Runic.Create@<VERSION>) or the dotnet new runic-app template, then dotnet tool restore and dotnet runic dev.

A minimal Window

In a project named MyApp:

// Counter.cs
using CommunityToolkit.Mvvm.ComponentModel;
using CommunityToolkit.Mvvm.Input;
using Runic.Application.Views.CsWebUi;

namespace MyApp;

public sealed partial class CounterViewModel : ObservableObject
{
    [ObservableProperty] private int count;

    [RelayCommand]
    private void Increment() => Count++;
}

// Selecting the Window makes the build generate Frontend/src/generated/counter.ts.
public sealed partial class CounterWindow(CsWebUiBridgeWindow<CounterViewModel> host)
    : CsWebUiWindow<CounterViewModel>(host);

// Program.cs
using CsWebUi;
using Microsoft.Extensions.DependencyInjection;
using MyApp;
using Runic.Application.Views.CsWebUi;

var services = new ServiceCollection();
services.AddScoped<CounterViewModel>();
services.AddRunicViews();
using var provider = services.BuildServiceProvider();

await using (var window = provider.OpenWindow<CounterWindow, CounterViewModel>(host => new CounterWindow(host)))
{
    window.SetRootFolder(Path.Combine(AppContext.BaseDirectory, "www"));
    window.Show("index.html");
    WebUiApplication.Wait();
}
WebUiApplication.Clean();

import { connectCounter } from "./generated/counter.js";

const counter = await connectCounter();
counter.subscribe(state => { document.querySelector("#count")!.textContent = String(state.count); });
document.querySelector("#increment")!.addEventListener("click", () => void counter.increment());

Generated modules import the shared browser runtime, so the frontend installs @runic-artifex/views (npm install @runic-artifex/views@preview) and bundles its entry. connectCounter() returns a CounterClient; subscribe delivers the current state first, calls reject with the runtime's BridgeError, and dispose() releases the connection. @runic-artifex/react, @runic-artifex/vue, @runic-artifex/svelte (useView) and @runic-artifex/angular (injectView()) bind clients to component lifetimes.

Frontend/index.html loads webui.js and the host's client script (runic-cswebui.js or runic-desktop-views.js) before the module. The First Window example is this application with a complete frontend.

Windows, Views, and composition

A partial RunicWindow<TViewModel> declares a window and its root ViewModel; a partial RunicView<TViewModel> selects the content presented for a ViewModel property. [RunicViewContract("name")] adds a second View for the same ViewModel. The build compiles the application, inspects these classes after the MVVM source generators run, and generates C# attachments and one ordinary TypeScript module per ViewModel.

A View is a logical .NET presentation object with typed DataContext. Its browser counterpart can be a plain TypeScript function or a framework component. The browser acknowledges mount and unmount, so a content session creates a fresh View for each presentation and releases it when the outlet changes. The ViewModel belongs to its application or window DI scope and may survive View changes. Window-local routes and operation admission are host-neutral; native window creation belongs to the host adapter.

The generated composition class (<ProjectName>.RunicBridgeComposition, or RunicBridgeCompositionType) provides two registrations:

• AddRunicViews() registers the generated Bridges, every non-Window View as transient, and ServiceProviderViewLocator as the default IRunicViewLocator. Register an earlier IRunicViewLocator or View to replace a default.
• AddRunicBridges() registers only the Bridges, for applications that create Views themselves or use another locator, such as ReactiveRunicViewLocator.

ViewModels stay explicit registrations because their lifetime is an application decision; a Window's root ViewModel must be scoped. The registrations are generated code, so they need no reflection and are NativeAOT-safe.

Presented content is bound to the window's model context, and keeps its checked-field registries, only while it is attached. Replacing, clearing, or pruning it releases both; the window keeps a weak identity so presenting the same object again returns the same reference. When the browser still shows a suspended reference, as after Main = b; Main = a; in one command, its mount resumes on the re-attached bridge with a fresh View. Snapshot revisions increase across the whole window, so a re-attached route never publishes an older revision. The wire protocol describes these rules.

Generated clients expose a snapshot, subscriptions, typed property setters, commands, and disposal. Calls reject with typed errors. Accepted operations remain owned by .NET across a browser reload; a reconnect gets a new snapshot. A transport failure after acceptance can leave completion unknown, so callers should inspect state before retrying a non-idempotent command. The generated field-write API returns receipts and version conflicts; frontend form helpers must await pending edits before issuing Save.

The runtime emits state and replies with generated and explicit Utf8JsonWriter code. The build tool inspects the compiled application; release runtime serialization does not reflect over ViewModel members. The first-window example is exercised through Native AOT and Chromium in CI. The generator's errors are listed under Generator diagnostics.

The First Window, CommunityToolkit Notes, and Reactive Notes examples exercise the packaged graph and generated client.

Generated TypeScript

Each ViewModel gets a module named after it (EditorViewModel becomes editor.ts) with its state interface, client interface and connect function. Every enum, DTO and union in the contract becomes one exported type named after its C# type, declared once in types.ts beside the modules. Next to each client, editor.mock.ts exports a typed test double, mockEditor; see Testing. Applications import it only from tests, so it is not bundled. Each module imports the named types it uses and re-exports them, so import type { DocumentPane } from "./generated/document.js" works too:

/// <summary>A pane of the document page.</summary>
public enum DocumentPane { Editor, Preview }

/// <summary>The pane the document currently shows.</summary>
public DocumentPane ActivePane => ...;

/** A pane of the document page. */
export type DocumentPane = "Editor" | "Preview";

• An enum is a union of its wire names (the C# names, or [RunicAlias]), so a switch over it can be exhaustive.
• A DTO is an interface with its wire member names. A [RunicUnion] is a union of its cases, discriminated by $case.
• Two C# types with the same name, or a name that collides with a generated declaration such as EditorState, are qualified with their namespace segments, for example NotesItem and TasksItem. Names are stable while no new collision appears: adding a same-named type, even in another ViewModel, qualifies the existing one too. Import the name your frontend uses and expect a compile error, not a silent change, when that happens. Generic DTOs append their arguments, for example PageOfNoteRow or BoxOfArrayOfInt32, and an enum without cases is never. A C# type named like a TypeScript reserved word is qualified the same way.
• A generic DTO member declared T is nullable where the type argument is: value: string in Box<string> and value: string | null in Box<string?>, and the generated .NET reader rejects null for the former. A member declared T? is always nullable. Members inherited from a generic base class follow the derived type's arguments, and a type without annotations, such as [RunicCommandInput(typeof(Box<string>))] or a union case, is non-nullable throughout. Uses whose members differ get separate declarations, for example BoxOfString and BoxOfNullableOfString; a type used only as Box<string?> keeps the plain name BoxOfString.
• A content property is the union of the PageReference types of the ViewModels it can present, such as DocumentPageReference | HomePageReference, with | null when it is nullable. A NavigationRegion<TContent> slot always includes | null, because a region can be empty; see Navigation.
• <summary> comments on ViewModels, state properties, commands, interactions, DTO types and members, and enum cases become TSDoc. The bootstrap pass writes the XML documentation file for this; a project that already writes one keeps its own. Set RunicBridgeDocumentation=false to skip it. A separate model assembly (RunicBridgeModelAssembly) needs its XML documentation file beside it.
• A command argument keeps the parameter name of its CommunityToolkit [RelayCommand] method. Other commands name it after the argument's C# type, or input for scalars.

Generator diagnostics

The generator reports every ViewModel's first problem in one build. An error names the type and member, and points at its source line when the inspected assembly has a portable PDB (the default). A member generated by a source generator, such as a CommunityToolkit [ObservableProperty], points at its [RelayCommand] method or its declaring class.

Build properties

The build targets ship in this package and apply to every project that references a host adapter. A project needs none of these properties unless it departs from the conventional Frontend folder.

dotnet build and dotnet publish copy the built frontend as loose files to www/ next to the executable; they do not embed it. dotnet runic dev sets RunicBridgeBuildFrontend=false and RunicBridgeCopyFrontend=false while its development server serves the frontend. The dotnet runic README lists the development-server properties it reads.

Bridge generation turns on by default for a project that references Runic.Application or builds in this repository. That default is optional: when the assembly declares no Runic Window or View, for example an application that only uses the navigator, the build generates nothing (and removes stale generated C# and TypeScript), skips the frontend install, build and copy steps, and succeeds with a normal-importance message. A publish that reuses an earlier build (--no-build) still copies an existing <frontend>/dist to www/. Generation is required, and RUNICBRIDGE006 stays an error for an assembly without a Window, when the project sets RunicBridgeBuildEnabled to true, or when it shows that it expects output: a package.json in RunicBridgeFrontendDir, RunicBridgeFrontendInput items, RunicBridgeCompositionType or RunicBridgeModelAssembly. Projects that reference a host adapter (Runic.Application.CsWebUi or Runic.Application.Desktop) always require generation, because the adapter sets RunicBridgeCompositionType. A navigator-only application should set RunicBridgeBuildEnabled to false: that also skips the nested bootstrap build, which optional mode still pays for.

A single-project application is compiled twice: a bootstrap pass with an empty generated composition, which the generator inspects, then the real build with the generated code. RunicBridgeBootstrap is true only in the bootstrap pass.

Typed commands and checked writes

CommunityToolkit IRelayCommand<T> and IAsyncRelayCommand<T> use the same supported input shapes and generated codecs as ReactiveUI commands: scalars, nullable values, DTOs, collections, unions, and explicit custom codecs. Generated canX(input) queries use the actual parameter. Async Toolkit commands expose startX, completion, recovery, and cancellation, with no invented result value. Toolkit cancellation calls the command's Cancel() and therefore targets its current execution; it does not isolate concurrent invocations of the same command instance.

[RelayCommand(IncludeCancelCommand = true)] is supported too. Toolkit's generated SaveCancelCommand exposes parameterless saveCancel() and canSaveCancel state in the web client. It executes the actual generated cancel command, so availability follows Toolkit's CanBeCanceled and cancellation targets the same native SaveCommand. The existing startSave operation still owns admission, completion, recovery, and View lifetime cancellation. Recognition requires Toolkit's generator metadata, the paired async command, and its cancellation-token method with IncludeCancelCommand = true; other plain ICommand properties still require [RunicCommandInput].

Checked-write receipts decode their values just like state: for example, an Int64 receipt's snapshot.value or conflict's incoming.value is a bigint. An identical request ID and payload replays its receipt. Reusing an ID with a different baseline version, baseline value, or new value produces a conflict. Each field retains at most 64 receipts within a default 256 KiB encoded-value and receipt-metadata budget. Evicted or oversized receipts leave bounded request-ID tombstones; reconcile authoritative state before issuing a new ID. The write may have succeeded even when its receipt could not be retained.

Batch synchronous model updates

using (BridgeSnapshotBatch.Begin(document))
{
    document.Title = imported.Title;
    document.Content = imported.Content;
    document.Language = imported.Language;
}

Nested scopes on the same model capture and publish one final snapshot per attached bridge when the outer scope ends. Notifications still advance the revision, and direct command/checked-write replies capture current state immediately. A batch controls snapshot work; it does not make mutations atomic or own the model scheduler. Enter the model's execution context as usual and keep the batch around synchronous changes, after awaiting I/O. The translations editor uses this during bulk document reconciliation and command result updates.

Structured validation

Models and nested DTOs may implement INotifyDataErrorInfo. Generated snapshots then expose validation.hasErrors, validation.truncated, and validation.errors, alongside existing property error string arrays. Each error contains a path of wire property names, list indexes, or dictionary keys and a message. Root entity errors use an empty path. Aliases are preserved, so a postal-code error might have the path ["profile", "postal-code"].

Return a BridgeValidationMessage from GetErrors to supply a stable Code, Severity, or relative CLR MemberPaths. Ordinary strings and ValidationResult remain supported. Generated metadata resolves paths without runtime reflection. Traversal and messages are bounded; truncated reports when validation details are incomplete. Nested ErrorsChanged notifications publish new validation state, and removed objects lose their subscriptions. This projection works across model frameworks; it does not run validation rules itself.

Use [RunicIgnore] on validation-only DTO properties such as a computed HasErrors; their values are represented by the validation projection.

Shared DTO exclusions

Public readable DTO properties are part of the Bridge contract, including computed properties. A DTO reader needs a public constructor matching its included properties, or public setters with a public parameterless constructor. Use [RunicIgnore] to leave a property on .NET without exposing it to the Bridge. By default, [JsonIgnore] affects System.Text.Json serialization only; it does not exclude a Bridge property.

For shared DTOs that already use System.Text.Json attributes, opt in from the assembly declaring the ViewModel:

using Runic.Application.Views;

[assembly: RunicBridgeJsonIgnore]

For example, a separate Core assembly can keep its DTO free of Runic dependencies:

using System.Text.Json.Serialization;

public sealed record HistoryQuery(string Message, string Author)
{
    [JsonIgnore]
    public bool IsFiltered => Message.Length != 0 || Author.Length != 0;
}

The opt-in excludes [JsonIgnore] and [JsonIgnore(Condition = JsonIgnoreCondition.Always)] throughout that ViewModel's DTO graphs, including nested DTOs, collections, command values, interactions and declared failures. Generated codecs, TypeScript, validation traversal and the Hot Reload fingerprint use the same exclusions. The Core assembly and the assembly declaring only a Window need no marker. Each ViewModel uses its own declaring assembly's policy.

Never, WhenWritingNull and WhenWritingDefault remain included; Bridge fields have a fixed contract and are emitted even when null or default. [RunicIgnore] always excludes a property, including one also marked [JsonIgnore(Condition = JsonIgnoreCondition.Never)]. Root ViewModel properties still use [RunicIgnore]; this opt-in applies to DTO properties only. Adding the marker can change an existing DTO wire contract and requires rebuilding the .NET application and generated frontend together.

Failure detail in development

A command, setter, checked write or operation that throws replies with a bounded message such as "Save failed." and is logged (see Logging and telemetry). In development the error also carries detail: {type, message, stack}, which the TypeScript runtime exposes as BridgeError.detail and the Vite plugin shows in DevTools. Development means DOTNET_ENVIRONMENT (or else ASPNETCORE_ENVIRONMENT) is Development, which dotnet runic dev sets. Set BridgeDiagnostics.IncludeFailureDetail to true or false to choose explicitly. Detail can contain file paths and application data, so do not enable it for a distributed build.

Declared failures

A command declares its expected failure type with [RunicFailure(typeof(SaveFailure))] on the command property or on its CommunityToolkit [RelayCommand] method, and signals it by throwing RunicFailureException(new TitleRequired()). The Bridge replies domain-failed with the encoded failure, in every environment and never with detail; an operation ends with the domain-failed status. Use [RunicUnion] for several cases. A value that is not the declared type, one that cannot be encoded, or one over 4 KiB is reported as an ordinary failure (event 1008). A synchronous command reports only failures thrown synchronously from Execute, so an async void plain ICommand cannot declare a failure that it throws after its first await. Operations exist only for asynchronous CommunityToolkit and ReactiveUI commands.

[RunicUnion(typeof(TitleRequired), typeof(TitleTaken))]
public abstract record SaveFailure;
[RunicUnionCase("titleRequired")] public sealed record TitleRequired : SaveFailure;
[RunicUnionCase("titleTaken")] public sealed record TitleTaken(string ExistingTitle) : SaveFailure;

[RelayCommand, RunicFailure(typeof(SaveFailure))]
private async Task SaveAsync(CancellationToken token)
{
    if (string.IsNullOrWhiteSpace(Title)) throw new RunicFailureException(new TitleRequired());
    // ...
}

The generated client's save() then returns Promise<BridgeOutcome<EditorState, SaveFailure>> instead of Promise<EditorState>, its operation is BridgeOperation<void, SaveFailure>, and the generated mock encodes the failure. A ReactiveUI command also reports the failure on ThrownExceptions, so give every bridged ReactiveCommand a subscriber.

Navigation (experimental)

Navigation comes from the Runic.Navigation package, which this package depends on. Its types, and the model context types, are in the Runic.Navigation namespace. Its README covers regions, transitions, ownership, results and disposal. Register it per window scope with services.AddRunicNavigation(), and give the window's session the navigator's model context; AddRunicNavigation() does that for windows opened from the scope.

Content slots

Expose a region as a get-only NavigationRegion<TContent> property, and the generator treats it as a content slot. The snapshot presents Current, or clears the slot when the region is empty. The wire value and TypeScript type are those of a nullable content property (for example DocumentPageReference | HomePageReference | null), so moving a non-null content property to a region adds | null, and the frontend must render the empty state. TContent must be an interface or base class of ViewModels with registered Views. A NavigationRegion<object> slot, or one with a public setter, is RUNICBRIDGE008.

The generated Bridge observes the region's Current and binds the window session to the navigator, so retiring owned content forgets its routes. A navigator serves one window, and the session must use the navigator's model context. Nothing is forwarded by hand, and ViewOutlets and test drivers (View<T>(vm => vm.Main)) work unchanged. Going back presents the same PageReference id with the retained model, and the outlet mounts a fresh View. Browser reload, remount and disconnect never touch entries.

Stale-route window. A commit retires and forgets departing owned content right away, while the frontend sees the new Current only with the next state capture. Until then it may still hold the old reference. An invocation on that reference is rejected like any forgotten route, and the outlet may briefly show the old View or nothing. The next capture converges.

Logging and telemetry

OpenWindow (CS-WebUI) and OpenDesktopWindowAsync (Desktop) pass the scope's ILoggerFactory to the Window's WindowContentSession when one is registered, for example with services.AddLogging(...). A session constructed directly takes it as loggerFactory. Without a factory, each entry is written to System.Diagnostics.Trace (TraceError, or TraceWarning for warnings) as its formatted message followed by the exception; a failed View mount goes to standard error instead.

Every entry carries the exception, in every environment: logs belong to the operator, whereas BridgeDiagnostics governs only what a Bridge reply shows to web content. Exception messages can contain application data, so treat log output accordingly. The message properties are listed per event.

Model is the ViewModel type name, Member the command or property, and Route the Bridge route (a content presentation's route is per instance, such as content12). A declared failure is an expected outcome, so it is logged at Debug, still with its exception; FailureType is the failure value's type.

Events 1000-1021 and 1050 use the category Runic.Application.Views (RunicViewsTelemetry.LogCategory). Event 1033 here is a window session's own model context failing to shut down, and uses the session's logger. Navigation (1060-1074) and the model context (1030-1033) log under Runic.Navigation and Runic.Navigation.RunicModelContext; see the Runic.Navigation logging section. Events 2000-2002 use Runic.Application.Desktop. Events 3000-3005 use Runic.Desktop and need DesktopHostOptions.LoggerFactory.

Events 1040-1042 come from Runic.Application.ReactiveUI (and its .Reactive flavor) and also use Runic.Application.Views. They need the ReactiveRoutedRegion<T>(router, loggerFactory) constructor, which a ViewModel can call with an ILoggerFactory injected from DI, as examples/notes-reactive-views does. Without a factory, the region writes the same messages to Trace as described above. Region is the region's ViewModel type name T. Event 1042 uses the logger passed to ObserveBridgeExceptions; Source is the observed command's expression, such as SaveCommand, or sourceName.

Bridge calls are traced by the ActivitySource and measured by the Meter named Runic.Application.Views (RunicViewsTelemetry.ActivitySourceName and MeterName). With OpenTelemetry, call AddSource(...) and AddMeter(...) with these names. Tag values are generated contract names, outcomes and exception types, never arguments or state.

Spans are named <kind> <Model>.<Member> and have the tags runic.bridge.kind, runic.bridge.model, runic.bridge.member, runic.bridge.route and runic.bridge.outcome. The outcome is ok, rejected, cancelled, failed, domain_failed or disconnected. An admission can also be unavailable, capacity, duplicate or expired, and an operation whose result could not be delivered is delivery_failed. A failed span has the status Error and error.type. A domain_failed call is an expected outcome: its span status stays Unset, it has no error.type, and runic.bridge.failures does not count it.

Route names are span tags but not metric tags, because content routes identify one instance. The duration histograms advise buckets from 0.5 ms to 10 s, and the size histogram from 256 B to 4 MiB. The queue depth reports the frames waiting for slow hosts across all Bridges when it is observed.

Incremental generation

The generator caches successful multi-view generation in its C# obj output directory. It hashes the model/dependency assemblies, generator assemblies, output-affecting options, and generated output contents. Missing or edited outputs invalidate the cache; unchanged generated files keep their timestamps. Set RUNIC_BRIDGE_CODEGEN_FORCE=1 or RUNIC_BRIDGE_CODEGEN_CACHE=0 to bypass it.

The configured frontend build command (RunicBridgeFrontendBuildCommand) runs only when one of its inputs is newer than obj/<Configuration>/<TargetFramework>/runic-bridge-frontend.stamp: files under RunicBridgeFrontendDir (excluding node_modules, dist, build, bin, obj and dot-directories), the generated TypeScript, and the project file. Generated TypeScript is rewritten only when its content changes, so C#-only edits skip the frontend build. Add RunicBridgeFrontendInput items, from a target that runs before RunicViewsGenerateBridge, for inputs outside the frontend directory such as workspace packages or generated assets; the translations editor is an example. Delete the stamp or rebuild to force a frontend build. Set RunicBridgeBuildFrontend=false when another tool, such as a running dev server, owns the frontend build; dotnet runic dev does this while its development server runs.

Generated C# and TypeScript files start with // <auto-generated />. Only such files are removed from the output directories when a ViewModel disappears, so RunicBridgeTypescriptDir may point into a directory with hand-written modules.

Accepted application work

Cancellation requests that a command stop; its invocation can finish before the underlying task completes. In particular, ReactiveUI bridge execution can settle a cancelled invocation and release its subscription while an uncooperative task continues recovery. WindowContentSession.BeginCloseAsync and its result's Completion drain bridge invocations. Their completion does not establish that independently accepted application work, durable changes, or recovery has finished.

Own such work with an AcceptedWorkScope in the scoped model or service that owns its resources. Pass a factory so ownership is registered before the task starts, and include recovery, publication, and cleanup in that task:

private readonly AcceptedWorkScope _acceptedWork = new();

public Task SaveAsync(CancellationToken cancellationToken) =>
    _acceptedWork.RunAsync(() => SaveAndRecoverAsync(cancellationToken));

public async ValueTask DisposeAsync()
{
    await _acceptedWork.DisposeAsync();
    // Release the model's resources after its accepted tasks finish.
}

RunAsync invokes its factory synchronously on the calling thread and returns the original task, preserving its result, failure, or cancellation. Concurrent drain includes accepted factories that have not yet returned a task. A null task or synchronous factory exception releases that admission and throws to the caller. Calls after drain starts throw InvalidOperationException without invoking the factory.

DrainAsync(cancellationToken) closes admission and waits for actual task completion, including faulted and cancelled tasks. Its cancellation token only stops that observer's wait; it neither cancels nor abandons owned work. Drain observes task failures without throwing them again, so callers still handle outcomes through their original tasks. DisposeAsync is idempotent and waits without cancellation. Keep resources alive through this drain even if a bridge invocation or an earlier drain observer has already been cancelled.

The scope does not serialize operations, dispatch model changes, request cancellation, or implement recovery. The application still owns those policies and must return a task that covers all work requiring its resources.