Agent Skills: Services Layer

Services Layer

Ground service guidance in apps/whispering/src/lib/services, its consumers, and the #platform/* mappings in apps/whispering/package.json. Historical examples and neighboring skills are leads, not current architecture.

Product Sentence

The service layer owns UI-free capabilities; callers inject app policy through explicit inputs, fallible operations return Results, and platform selection has one build-time owner.

Boundary

Services may perform IO and may own service-local runtime state. They are not required to be pure functions. They must remain free of UI and app-owned policy:

• no runtime reads of Svelte stores, settings, deviceConfig, toasts, or report;
• accept credentials, model names, endpoints, paths, and user choices as inputs;
• return domain data and errors, not presentation copy or UI state;
• expose the same contract from both sides of a #platform/* seam.

$lib/operations usually reads app settings, chooses providers, and composes services. $lib/queries adds shared query identity and observable lifecycle only when the UI needs it.

The transcription directory also holds provider registry data and the UI-facing provider-ui.ts join. Those colocated metadata modules are not service implementations; do not use them to weaken the service boundary.

Model Fallibility Honestly

Use Result<T, E> for a public operation that can fail in ordinary runtime use. Adapt throwing platform or library calls with the error-handling skill.

Do not fake a Result for an infallible in-memory action or cleanup. Current examples include local shortcut register / unregister returning void and listener setup returning a cleanup function.

export type DownloadService = {
	downloadBlob(args: {
		name: string;
		blob: Blob;
	}): Promise<Result<void, DownloadError>>;
};

Errors belong to the layer that understands the failure. Preserve lower-layer tagged errors when composing services. Define a service-local variant only for a failure the service itself owns. Use define-errors for variant shape and message rules; use error-handling for adaptation and propagation.

Direct Object Or Factory

Default to a direct *ServiceLive object when construction has no input or lifecycle. Current download, analytics, text, and transcription provider implementations use this shape. Download, analytics, and text check their shared platform contracts with satisfies <Service>.

Use a factory when it owns real construction inputs, replaceable dependencies, or stateful lifecycle. The browser and CPAL recorder factories earn their boundary because each creates recording sessions with stop, cancel, subscribe, and teardown behavior.

Do not add create* plus *Live mechanically for a stateless object.

Read service implementation patterns for the current direct-object example and the factory decision.

Platform And Runtime Selection

Use #platform/* imports for a capability with browser and Tauri implementations. package.json#imports chooses the implementation at build time; shared callers import one stable name and do not inspect window.__TAURI_INTERNALS__.

Use the nullable #platform/tauri namespace for Tauri-only capabilities.

User-selected providers are runtime policy, not a platform seam. Keep the dispatch in the consuming operation. Whispering transcription reads the selected provider in $lib/operations/transcribe.ts; the query layer only observes that operation.

Read service organization and platform variants when adding or moving a platform service.

Service Barrel

$lib/services/index.ts collects stable cross-platform capabilities:

export const services = {
	analytics: AnalyticsServiceLive,
	text: TextServiceLive,
	blobs: BlobsLive,
	blobSources: BlobSourcesLive,
	download: DownloadServiceLive,
	localShortcutManager: LocalShortcutManagerLive,
	sound: PlaySoundServiceLive,
} as const;

Do not force every provider implementation into this barrel. A runtime operation may import its provider-specific services directly when it owns the dispatch table.

Final Check

• The service imports no UI or app-owned settings.
• Every app choice enters as an explicit input or is selected by the caller.
• Fallible public operations return Results; infallible operations stay plain.
• A factory owns construction or lifecycle, not convention alone.
• Platform choice happens through one #platform/* mapping.
• Runtime provider choice happens once at the consuming operation.
• Lower-layer errors pass through unless this service owns a new failure.