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, 242 insertions, 0 deletions

diff --git a/src/features/cache-warming/logic/view-model.ts b/src/features/cache-warming/logic/view-model.ts
new file mode 100644
index 0000000..f7740d7
--- /dev/null
+++ b/src/features/cache-warming/logic/view-model.ts
@@ -0,0 +1,242 @@
+import type { SurfaceSpec } from "@dispatch/ui-contract";
+
+/**
+ * Pure core for the cache-warming view — zero DOM, zero effects, zero Svelte.
+ *
+ * The backend's `cache-warming` surface carries a toggle, a number interval (in
+ * seconds), two `stat`s ("last cache rate" + "cache retention"), and a `custom`
+ * `cache-warming-timer` field bearing the AUTHORITATIVE `nextWarmAt`/`lastWarmAt`
+ * epoch-ms timestamps. This module turns those inputs into the view-model the
+ * (thin) Svelte component renders: parsed controls, a warming-history reducer
+ * keyed off the authoritative `lastWarmAt`, an authoritative countdown, and the
+ * status/format helpers.
+ */
+
+// ── Manual-warm port (consumer-defines-port; the composition root adapts the
+//    store's `POST /chat/warm` result to this shape). ──────────────────────────
+export type WarmFeedback =
+	| { readonly ok: true; readonly cachePct: number; readonly expectedCacheRate: number }
+	| { readonly ok: false; readonly error: string };
+
+export type WarmNow = () => Promise<WarmFeedback | null>;
+
+// ── Parsed surface controls ───────────────────────────────────────────────────
+
+export interface ParsedControls {
+	readonly enabled: boolean;
+	readonly toggleActionId: string | null;
+	readonly intervalSeconds: number;
+	readonly setIntervalActionId: string | null;
+	/** Most recent warm's cache-hit %, from the "last cache rate" stat (`null` when "—"/absent). */
+	readonly lastPct: number | null;
+	/** Cross-turn retention %, from the "cache retention" stat (`null` when "—"/absent). */
+	readonly retentionPct: number | null;
+	/** Authoritative epoch-ms the next AUTOMATIC warm fires, or `null` when not scheduled. */
+	readonly nextWarmAt: number | null;
+	/** Authoritative epoch-ms of the most recent completed warm, or `null` if none. */
+	readonly lastWarmAt: number | null;
+}
+
+const EMPTY_CONTROLS: ParsedControls = {
+	enabled: false,
+	toggleActionId: null,
+	intervalSeconds: 0,
+	setIntervalActionId: null,
+	lastPct: null,
+	retentionPct: null,
+	nextWarmAt: null,
+	lastWarmAt: null,
+};
+
+/** The `cache-warming-timer` custom field's renderer id (this feature owns it). */
+const TIMER_RENDERER_ID = "cache-warming-timer";
+
+/** Parse a stat's display string (e.g. "100%", "93 %", "—") into a number or null. */
+export function parsePct(value: string): number | null {
+	const match = value.match(/-?\d+(?:\.\d+)?/);
+	if (match === null) return null;
+	const n = Number(match[0]);
+	return Number.isFinite(n) ? n : null;
+}
+
+/** A finite number, else null. */
+function numOrNull(v: unknown): number | null {
+	return typeof v === "number" && Number.isFinite(v) ? v : null;
+}
+
+/** Pull the authoritative `nextWarmAt`/`lastWarmAt` out of the timer custom payload. */
+function parseTimer(payload: unknown): { nextWarmAt: number | null; lastWarmAt: number | null } {
+	if (typeof payload !== "object" || payload === null) {
+		return { nextWarmAt: null, lastWarmAt: null };
+	}
+	const p = payload as Record<string, unknown>;
+	return { nextWarmAt: numOrNull(p.nextWarmAt), lastWarmAt: numOrNull(p.lastWarmAt) };
+}
+
+/**
+ * Extract the cache-warming controls from the surface spec by FIELD KIND. The
+ * surface has one toggle, one number, two stats (rate + retention, told apart by
+ * label), and one `custom` timer field. Returns empty defaults when the spec is
+ * absent.
+ */
+export function parseControls(spec: SurfaceSpec | null): ParsedControls {
+	if (spec === null) return EMPTY_CONTROLS;
+	let enabled = false;
+	let toggleActionId: string | null = null;
+	let intervalSeconds = 0;
+	let setIntervalActionId: string | null = null;
+	let lastPct: number | null = null;
+	let retentionPct: number | null = null;
+	let nextWarmAt: number | null = null;
+	let lastWarmAt: number | null = null;
+	let seenToggle = false;
+	let seenNumber = false;
+	let seenRateStat = false;
+	for (const field of spec.fields) {
+		if (field.kind === "toggle" && !seenToggle) {
+			enabled = field.value;
+			toggleActionId = field.action.actionId;
+			seenToggle = true;
+		} else if (field.kind === "number" && !seenNumber) {
+			intervalSeconds = field.value;
+			setIntervalActionId = field.action.actionId;
+			seenNumber = true;
+		} else if (field.kind === "stat") {
+			// Retention is told apart by its label; everything else is the cache rate
+			// (first one wins, so a stray later stat can't clobber it).
+			if (/retention/i.test(field.label)) {
+				retentionPct = parsePct(field.value);
+			} else if (!seenRateStat) {
+				lastPct = parsePct(field.value);
+				seenRateStat = true;
+			}
+		} else if (field.kind === "custom" && field.rendererId === TIMER_RENDERER_ID) {
+			const timer = parseTimer(field.payload);
+			nextWarmAt = timer.nextWarmAt;
+			lastWarmAt = timer.lastWarmAt;
+		}
+	}
+	return {
+		enabled,
+		toggleActionId,
+		intervalSeconds,
+		setIntervalActionId,
+		lastPct,
+		retentionPct,
+		nextWarmAt,
+		lastWarmAt,
+	};
+}
+
+// ── Interval ↔ minutes/seconds (seconds capped at 59) ─────────────────────────
+
+export interface MinSec {
+	readonly minutes: number;
+	readonly seconds: number;
+}
+
+export function clampSeconds(n: number): number {
+	if (!Number.isFinite(n)) return 0;
+	return Math.min(59, Math.max(0, Math.floor(n)));
+}
+
+export function clampMinutes(n: number): number {
+	if (!Number.isFinite(n)) return 0;
+	return Math.max(0, Math.floor(n));
+}
+
+export function toMinSec(totalSeconds: number): MinSec {
+	const total = Math.max(0, Math.floor(totalSeconds));
+	return { minutes: Math.floor(total / 60), seconds: total % 60 };
+}
+
+/** Combine a minutes + seconds pair (each clamped) into total seconds. */
+export function fromMinSec(minutes: number, seconds: number): number {
+	return clampMinutes(minutes) * 60 + clampSeconds(seconds);
+}
+
+// ── Status + formatting ───────────────────────────────────────────────────────
+
+export type WarmStatus = "success" | "warning" | "error";
+
+/** Cache-hit % → semantic status (green high, yellow mid, red low). */
+export function statusForPct(pct: number): WarmStatus {
+	if (pct >= 80) return "success";
+	if (pct >= 40) return "warning";
+	return "error";
+}
+
+/** A status → its DaisyUI text-colour class (full literal so Tailwind keeps it). */
+export function colorClass(status: WarmStatus): string {
+	switch (status) {
+		case "success":
+			return "text-success";
+		case "warning":
+			return "text-warning";
+		case "error":
+			return "text-error";
+	}
+}
+
+/** The status line for a warm, matching the manual-warm feedback phrasing. */
+export function formatWarmLabel(pct: number): string {
+	return `Warmed — ${Math.round(pct)}% cache hit`;
+}
+
+/** Seconds → a short countdown string (e.g. "3:05", "9s"). */
+export function formatCountdown(seconds: number): string {
+	const s = Math.max(0, Math.floor(seconds));
+	if (s < 60) return `${s}s`;
+	const m = Math.floor(s / 60);
+	const rem = s % 60;
+	return `${m}:${String(rem).padStart(2, "0")}`;
+}
+
+// ── Warming history reducer (keyed off the authoritative `lastWarmAt`) ─────────
+
+export interface WarmEntry {
+	readonly pct: number;
+	/** Authoritative epoch-ms of this warm (the surface's `lastWarmAt`). */
+	readonly at: number;
+}
+
+export interface WarmingViewState {
+	/** Warmings, MOST RECENT FIRST. */
+	readonly history: readonly WarmEntry[];
+	/** The last authoritative `lastWarmAt` recorded, for change-detection (de-dup key). */
+	readonly lastWarmAt: number | null;
+}
+
+const MAX_HISTORY = 50;
+
+export function initialWarmingState(): WarmingViewState {
+	return { history: [], lastWarmAt: null };
+}
+
+/**
+ * Fold the surface's authoritative `lastWarmAt` + current "last cache rate" into
+ * history. Records a new entry only when `lastWarmAt` CHANGED (a toggle/interval
+ * update re-pushes the same timestamp → no entry), de-duplicated on the timestamp
+ * (not the pct, so two warms with the same % both count). A null `lastWarmAt` is
+ * ignored; a null pct advances the de-dup key without adding an entry.
+ */
+export function observeWarm(
+	state: WarmingViewState,
+	lastWarmAt: number | null,
+	pct: number | null,
+): WarmingViewState {
+	if (lastWarmAt === null || lastWarmAt === state.lastWarmAt) return state;
+	if (pct === null) return { ...state, lastWarmAt };
+	const history = [{ pct, at: lastWarmAt }, ...state.history].slice(0, MAX_HISTORY);
+	return { history, lastWarmAt };
+}
+
+/**
+ * Seconds until the next automatic warm, AUTHORITATIVE: derived straight from the
+ * backend's `nextWarmAt` epoch-ms (never FE-anchored/guessed). `null` when nothing
+ * is scheduled (disabled, or a turn is generating so the timer is cancelled).
+ */
+export function secondsUntilNext(nextWarmAt: number | null, now: number): number | null {
+	if (nextWarmAt === null) return null;
+	return Math.max(0, Math.ceil((nextWarmAt - now) / 1000));
+}