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, 10 insertions, 1 deletions

diff --git a/src/features/chat/ui/ChatView.svelte b/src/features/chat/ui/ChatView.svelte
index 3d1421d..00691aa 100644
--- a/src/features/chat/ui/ChatView.svelte
+++ b/src/features/chat/ui/ChatView.svelte
@@ -3,10 +3,12 @@
 	import {
 		interleaveTurnMetrics,
 		viewCacheRate,
+		viewExpectedCache,
 		viewStepMetrics,
 		viewTurnMetrics,
 		type TurnMetricsEntry,
 	} from "../../../core/metrics";
+	import { Markdown } from "../../markdown";
 
 	const badgeClass = {
 		success: "badge-success",
@@ -113,7 +115,7 @@
 		<div class="chat chat-start [&>.chat-bubble]:max-w-5xl">
 			<div class="chat-bubble w-full bg-transparent">
 				{#if rendered.chunk.type === "text"}
-					<p>{rendered.chunk.text}</p>
+					<Markdown text={rendered.chunk.text} streaming={rendered.streaming ?? false} />
 				{:else if rendered.chunk.type === "error"}
 					<div class="text-error" role="alert">
 						{rendered.chunk.message}
@@ -146,6 +148,7 @@
 			{@const turnView = viewTurnMetrics(row.turn)}
 			{@const lastCache = viewCacheRate(row.turn.usage)}
 			{@const chatCache = viewCacheRate(row.cumulativeUsage)}
+			{@const retention = viewExpectedCache(row.turn.usage, row.prevTurnUsage)}
 			<div class="chat chat-start">
 				<div class="chat-bubble w-full max-w-5xl bg-transparent p-0">
 					<div class="flex flex-col gap-1 text-xs">
@@ -163,6 +166,12 @@
 								<span class="opacity-70">Chat Total:</span>
 								<span class="badge badge-sm {badgeClass[chatCache.level]}">{chatCache.pct}%</span>
 							</span>
+							{#if retention}
+								<span class="flex items-center gap-1">
+									<span class="opacity-70">Retention:</span>
+									<span class="badge badge-sm {badgeClass[retention.level]}">{retention.pct}%</span>
+								</span>
+							{/if}
 						</div>
 					</div>
 				</div>