soma: Toast pilot — multi-instance runtime + trigger() integration

Commit B of the Toast pilot. The runtime.trigger() contract from commit A
now has its first real consumer: all three dismiss paths route through
`runtime.trigger('dismiss')`, which emits the perceptual signal one frame
before the toaster mutates state.

Multi-instance architecture validated
Toast is the first component with multiple per-instance subtrees: each
toast in the queue is its own scope with its own children. Two runtime
instances coexist per Toast tree:

  ToastProvider (root)
    └── runtime instance A — registers `viewport` only
  ToastItemProvider (one per active toast in queue)
    └── runtime instance B — registers `item` + its children
                              (`title`, `description`, `action`, `close`)

`partRef('item')` resolves to THIS toast's element because the lookup
happens on THIS Item's runtime, not a shared one. `runtime.trigger('dismiss')`
on Item-B targets Item-B's DOM element. Per-toast isolation by construction.

dismiss wired through runtime.trigger
Three call sites now go through the same path instead of calling
`toaster.dismiss(id)` directly:
- ToastCloseProvider.onclick (user clicks the × button)
- ToastItemProvider startTimer setTimeout callback (auto-dismiss)
- ToastItemProvider onpointerup (swipe gesture meets threshold)

The runtime fires `data-event="dismiss"` on the item, awaits one rAF for
CSS to observe it, then calls the dismiss handler that mutates
`toast.dismissing = true`. The item's effect re-derives `data-state="closed"`
from `isOpen = !dismissing` and writes it via dom.apply on the next tick.

intent-driven role / aria-live still works
The morfo's `mapRef(propRef('intent'), { neutral: 'status', risk: 'alert', … })`
for `role` and `aria-live` is resolved by the runtime per-Item: each toast
reads its own `intent` from `opts.toast.current.intent` via the per-Item
runtime sources. Risk/threat toasts get `role=alert` + `aria-live=assertive`;
the others get `role=status` + `aria-live=polite`. No code in the provider
selects this — the morfo declares it, the resolver computes it.

Per-part props
Action's `altText` is per-instance per-action — passed to the runtime via
`registerPart('action', { props: { altText: () => opts.altText.current } })`.
Validates that the runtime's per-part source override (introduced in
commit 8ede5353 but never exercised) works as designed.

Translation lookup
Close's `aria-label` resolves through `v.translationRef` against the Item
runtime's `translate` source (`soma.langs.ts`). Confirms translationRef
ergonomics through the runtime path.

What this commit does NOT do (deferred)
- `present` and `announce` events: declared in the morfo but not wired.
  Would fire on Item mount; needs a small effect at the right phase.
- `runtime.keydown` for Item's `Escape` keyboard declaration: requires
  the V2 runtime API.
- presence layer (data-starting-style/data-ending-style) still flows
  through Svelte render — not migrated to dom.apply. Mixed model is OK
  while the boundary is clearly between morfo-declared attrs (runtime)
  and layer-declared transitions (Svelte).

Verification
- 84/84 focused unit tests green.
- 66/66 morfo-check (toast included).
- 68/68 smoke routes 200 OK.
- svelte-check unchanged at 155.

src/uix/soma/components/toast/toast-provider.svelte.ts

@@ -1,14 +1,19 @@
 import { Provider, context, type ProviderOpts, type WithRefOpts } from '../../provider';
-import { readableActive, state, type Active, type ActiveProps } from '../../reactive';
+import { createAttrs, registerContract } from '../../attrs';
+import { readableActive, state, type ActiveProps } from '../../reactive';
 import type { SomaMouseEvent } from '../../types';
 import { Soma } from '../../core/soma.svelte';
 import { isBrowser } from '../../dom';
+import { createMorfoRuntime, type MorfoRuntime } from '../../morfo';
 import { Presence } from '../../layers/presence.svelte';
 import type { Toaster, ToastData, SwipeDirection } from './toaster.svelte';
 
 import { toastMorfo } from '../../../morfo/components/toast';
 
-// ── Provider (root, no DOM) ─────────────────────────────────────────────────
+createAttrs(toastMorfo);
+registerContract(toastMorfo);
+
+// ── Provider (root, virtual) ────────────────────────────────────────────────
 
 interface ToastProviderOpts
 	extends
@@ -20,17 +25,33 @@ interface ToastProviderOpts
 
 export class ToastProvider extends Provider<ToastProviderOpts> {
 	static readonly ctx = context<ToastProvider>('Toast');
-	static get(): ToastProvider | undefined { return this.ctx.getOr(undefined) as ToastProvider | undefined; }
+	static get(): ToastProvider | undefined {
-	static require(): ToastProvider { return this.ctx.get(); }
+		return this.ctx.getOr(undefined) as ToastProvider | undefined;
+	}
+	static require(): ToastProvider {
+		return this.ctx.get();
+	}
 
 	static create(opts: ToastProviderOpts) {
 		return new ToastProvider(opts);
 	}
 
 	readonly soma = Soma.get();
+	readonly runtime: MorfoRuntime;
 
 	private constructor(opts: ToastProviderOpts) {
 		super(opts, { morfo: toastMorfo, part: 'provider' }, ToastProvider.ctx);
+
+		// Root-scope runtime — only the Viewport part registers here. Item and
+		// its children get their own runtime per-instance (see ToastItemProvider).
+		const soma = Soma.require();
+		this.runtime = createMorfoRuntime(toastMorfo, {
+			dom: soma.dom,
+			semantic: soma.semantic,
+			props: {
+				label: () => opts.label.current
+			}
+		});
 	}
 
 	get toaster(): Toaster {
@@ -53,6 +74,10 @@ export class ToastViewportProvider extends Provider<ToastViewportOpts> {
 	private constructor(opts: ToastViewportOpts) {
 		super(opts, { morfo: toastMorfo, part: 'viewport' });
 		this.provider = ToastProvider.require();
+		this.provider.runtime.registerPart('viewport', {
+			id: opts.id,
+			ref: opts.ref
+		});
 
 		// Register global hotkey to focus viewport, with cleanup. Supports
 		// composite hotkeys like `['AltLeft', 'F8']` by tracking currently
@@ -67,7 +92,6 @@ export class ToastViewportProvider extends Provider<ToastViewportOpts> {
 				return hotkey.every((k) => {
 					if (e.code === k || e.key === k) return true;
 					if (pressed.has(k)) return true;
-					// Treat modifier aliases as currently active.
 					if ((k === 'Alt' || k === 'AltLeft' || k === 'AltRight') && e.altKey) return true;
 					if ((k === 'Control' || k === 'ControlLeft' || k === 'ControlRight') && e.ctrlKey)
 						return true;
@@ -117,12 +141,7 @@ export class ToastViewportProvider extends Provider<ToastViewportOpts> {
 
 	readonly props = $derived.by(() =>
 		this.assertProps({
-			...this.baseProps,
+			...this.provider.runtime.partProps('viewport'),
-			...this.resolveMorfoProps({
-				props: {
-					label: this.provider.opts.label.current
-				}
-			}),
 			tabindex: -1
 		} as const)
 	);
@@ -139,8 +158,12 @@ interface ToastItemOpts
 
 export class ToastItemProvider extends Provider<ToastItemOpts> {
 	static readonly ctx = context<ToastItemProvider>('ToastItem');
-	static get(): ToastItemProvider | undefined { return this.ctx.getOr(undefined) as ToastItemProvider | undefined; }
+	static get(): ToastItemProvider | undefined {
-	static require(): ToastItemProvider { return this.ctx.get(); }
+		return this.ctx.getOr(undefined) as ToastItemProvider | undefined;
+	}
+	static require(): ToastItemProvider {
+		return this.ctx.get();
+	}
 
 	static create(opts: ToastItemOpts) {
 		return new ToastItemProvider(opts);
@@ -149,6 +172,13 @@ export class ToastItemProvider extends Provider<ToastItemOpts> {
 	readonly provider: ToastProvider;
 	readonly presence: Presence;
 
+	/**
+	 * Per-instance runtime. Every toast in the queue is its own scope:
+	 * `partRef('item')` must resolve to THIS toast's element, not any other.
+	 * Title / Description / Action / Close inside this Item register here.
+	 */
+	readonly runtime: MorfoRuntime;
+
 	// tracked IDs for ARIA
 	titleId = state('');
 	descriptionId = state('');
@@ -174,6 +204,39 @@ export class ToastItemProvider extends Provider<ToastItemOpts> {
 		super(opts, { morfo: toastMorfo, part: 'item' }, ToastItemProvider.ctx);
 		this.provider = ToastProvider.require();
 
+		// Per-instance runtime for { item, title, description, action, close }.
+		// `events.dismiss` is the WHEN — runtime.trigger('dismiss') runs the
+		// perceptual signal first, then this callback mutates state, then the
+		// item's effect re-derives data-state etc. via dom.apply.
+		const soma = Soma.require();
+		this.runtime = createMorfoRuntime(toastMorfo, {
+			dom: soma.dom,
+			semantic: soma.semantic,
+			states: {
+				open: () => this.isOpen
+			},
+			props: {
+				intent: () => opts.toast.current.intent,
+				loading: () => opts.toast.current.loading,
+				swipeState: () => (this.swipeState === 'idle' ? undefined : this.swipeState),
+				swipeDirection: () => this.provider.toaster.swipeDirection
+			},
+			parts: {
+				title: () => this.titleId.current || undefined,
+				description: () => this.descriptionId.current || undefined
+			},
+			translate: (key) => soma.langs.ts(key),
+			events: {
+				dismiss: () => {
+					this.provider.toaster.dismiss(opts.toast.current.id);
+				}
+			}
+		});
+		this.runtime.registerPart('item', {
+			id: opts.id,
+			ref: opts.ref
+		});
+
 		// Presence for exit animation
 		this.presence = new Presence({
 			open: readableActive(() => this.isOpen),
@@ -216,7 +279,7 @@ export class ToastItemProvider extends Provider<ToastItemOpts> {
 		this.clearTimer();
 		this.startTime = Date.now();
 		this.timerId = setTimeout(() => {
-			this.provider.toaster.dismiss(this.opts.toast.current.id);
+			void this.runtime.trigger('dismiss');
 		}, this.remaining);
 	}
 
@@ -337,7 +400,7 @@ export class ToastItemProvider extends Provider<ToastItemOpts> {
 
 		if (isCorrectDirection && Math.abs(delta) >= this.swipeThreshold) {
 			this.swipeState = 'end';
-			this.provider.toaster.dismiss(this.opts.toast.current.id);
+			void this.runtime.trigger('dismiss');
 		} else {
 			this.swipeState = 'cancel';
 			this.swipeDeltaX = 0;
@@ -351,22 +414,7 @@ export class ToastItemProvider extends Provider<ToastItemOpts> {
 
 	readonly props = $derived.by(() =>
 		this.assertProps({
-			...this.baseProps,
+			...this.runtime.partProps('item'),
-			...this.resolveMorfoProps({
-				states: {
-					open: this.isOpen
-				},
-				props: {
-					intent: this.opts.toast.current.intent,
-					loading: this.opts.toast.current.loading,
-					swipeState: this.swipeState === 'idle' ? undefined : this.swipeState,
-					swipeDirection: this.provider.toaster.swipeDirection
-				},
-				parts: {
-					title: this.titleId.current || undefined,
-					description: this.descriptionId.current || undefined
-				}
-			}),
 			tabindex: 0,
 			style: {
 				'--soma-toast-swipe-move-x': `${this.swipeDeltaX}px`,
@@ -403,15 +451,21 @@ export class ToastTitleProvider extends Provider<ToastTitleOpts> {
 		return new ToastTitleProvider(opts);
 	}
 
+	readonly toastItem: ToastItemProvider;
+
 	private constructor(opts: ToastTitleOpts) {
 		super(opts, { morfo: toastMorfo, part: 'title' });
-		const toastItem = ToastItemProvider.require();
+		this.toastItem = ToastItemProvider.require();
-		toastItem.titleId.current = opts.id.current;
+		this.toastItem.titleId.current = opts.id.current;
+		this.toastItem.runtime.registerPart('title', {
+			id: opts.id,
+			ref: opts.ref
+		});
 	}
 
 	readonly props = $derived.by(() =>
 		this.assertProps({
-			...this.baseProps
+			...this.toastItem.runtime.partProps('title')
 		} as const)
 	);
 }
@@ -425,15 +479,21 @@ export class ToastDescriptionProvider extends Provider<ToastDescriptionOpts> {
 		return new ToastDescriptionProvider(opts);
 	}
 
+	readonly toastItem: ToastItemProvider;
+
 	private constructor(opts: ToastDescriptionOpts) {
 		super(opts, { morfo: toastMorfo, part: 'description' });
-		const toastItem = ToastItemProvider.require();
+		this.toastItem = ToastItemProvider.require();
-		toastItem.descriptionId.current = opts.id.current;
+		this.toastItem.descriptionId.current = opts.id.current;
+		this.toastItem.runtime.registerPart('description', {
+			id: opts.id,
+			ref: opts.ref
+		});
 	}
 
 	readonly props = $derived.by(() =>
 		this.assertProps({
-			...this.baseProps
+			...this.toastItem.runtime.partProps('description')
 		} as const)
 	);
 }
@@ -452,18 +512,26 @@ export class ToastActionProvider extends Provider<ToastActionOpts> {
 		return new ToastActionProvider(opts);
 	}
 
+	readonly toastItem: ToastItemProvider;
+
 	private constructor(opts: ToastActionOpts) {
 		super(opts, { morfo: toastMorfo, part: 'action' });
+		this.toastItem = ToastItemProvider.require();
+
+		// Per-part props: `altText` lives on Action's own opts, not on the Item.
+		// Pass it via registerPart so the Action's effect resolves it locally.
+		this.toastItem.runtime.registerPart('action', {
+			id: opts.id,
+			ref: opts.ref,
+			props: {
+				altText: () => opts.altText.current
+			}
+		});
 	}
 
 	readonly props = $derived.by(() =>
 		this.assertProps({
-			...this.baseProps,
+			...this.toastItem.runtime.partProps('action')
-			...this.resolveMorfoProps({
-				props: {
-					altText: this.opts.altText.current
-				}
-			})
 		} as const)
 	);
 }
@@ -482,19 +550,32 @@ export class ToastCloseProvider extends Provider<ToastCloseOpts> {
 	private constructor(opts: ToastCloseOpts) {
 		super(opts, { morfo: toastMorfo, part: 'close' });
 		this.toastItem = ToastItemProvider.require();
+		this.toastItem.runtime.registerPart('close', {
+			id: opts.id,
+			ref: opts.ref
+		});
 	}
 
+	/**
+	 * Routes through `runtime.trigger('dismiss')` rather than calling
+	 * `toaster.dismiss(...)` directly. The runtime emits the perceptual signal
+	 * (`data-event="dismiss"` on the item) one frame before the structural
+	 * change, then invokes the dismiss handler that mutates the toaster state.
+	 *
+	 * `void` is intentional — DOM event handlers must be sync; the trigger's
+	 * Promise chain runs in the background.
+	 */
 	readonly onclick = (_e: SomaMouseEvent<HTMLButtonElement>) => {
-		this.toastItem.provider.toaster.dismiss(this.toastItem.opts.toast.current.id);
+		void this.toastItem.runtime.trigger('dismiss');
 	};
 
 	readonly props = $derived.by(() =>
 		this.assertProps({
-			...this.baseProps,
+			...this.toastItem.runtime.partProps('close'),
-			...this.resolveMorfoProps({
-				translations: (key) => this.toastItem.provider.soma?.langs.ts(key)
-			}),
 			onclick: this.onclick
 		} as const)
 	);
 }
+
+// `SwipeDirection` is re-exported by toaster.svelte.ts; nothing else here uses it.
+export type { SwipeDirection };