feat(cache-warming,surfaces,metrics,markdown): conversation-scoped surfaces, cache warming + retention, markdown

Consumes the backend cache-warming + cache-rate handoffs end-to-end and adds supporting infra:

- protocol/transport: conversation-scoped surfaces (conversationId on subscribe/invoke/surface + staleness routing); store auto-subscribes the catalog with the focused conversation and re-scopes on switch.
- surface-host: generic Number field renderer + custom rendererId dispatch (graceful skip on unknown).
- cache-warming feature: enabled toggle, min+sec interval, AUTHORITATIVE countdown from the surface's cache-warming-timer nextWarmAt, manual Warm now (POST /chat/warm), lastWarmAt-keyed history, cache-retention stat, expectedCacheRate headline.
- metrics: cross-turn expected-cache (retention) derivation + bubble badge; cache-rate fix needs no code change (inputTokens now total).
- markdown feature: marked + marked-highlight + highlight.js + dompurify, rendered in ChatView.
- fixes (gemini review): {#key activeConversationId} remount of CacheWarmingView to stop history/feedback leaking across tabs; guard NaN interval inputs from committing 0.
- docs/contracts: regenerated transport/ui-contract mirrors; backend-handoff updated (CR-3 resolved).

Verified: svelte-check 0 errors, biome clean, 494 tests pass, vite build OK.

1 files changed, 3 insertions, 0 deletions

diff --git a/src/features/surface-host/ui/SurfaceView.svelte b/src/features/surface-host/ui/SurfaceView.svelte
index 5210e8c..24be8b8 100644
--- a/src/features/surface-host/ui/SurfaceView.svelte
+++ b/src/features/surface-host/ui/SurfaceView.svelte
@@ -2,6 +2,7 @@
 	import type { InvokeMessage, SurfaceSpec } from "@dispatch/ui-contract";
 	import { groupRenderFields, planSurface } from "../logic/plan";
 	import Button from "./Button.svelte";
+	import Number from "./Number.svelte";
 	import Progress from "./Progress.svelte";
 	import Selector from "./Selector.svelte";
 	import StatTable from "./StatTable.svelte";
@@ -30,6 +31,8 @@
 			<Progress field={group.field} />
 		{:else if group.field.kind === "selector"}
 			<Selector field={group.field} surfaceId={spec.id} {onInvoke} />
+		{:else if group.field.kind === "number"}
+			<Number field={group.field} surfaceId={spec.id} {onInvoke} />
 		{:else if group.field.kind === "button"}
 			<Button field={group.field} surfaceId={spec.id} {onInvoke} />
 		{:else if group.field.kind === "custom"}