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, 102 insertions, 8 deletions

diff --git a/src/core/protocol/reducer.test.ts b/src/core/protocol/reducer.test.ts
index 57e12f2..c8e517a 100644
--- a/src/core/protocol/reducer.test.ts
+++ b/src/core/protocol/reducer.test.ts
@@ -1,5 +1,12 @@
 import { describe, expect, it } from "vitest";
-import { applyServerMessage, initialState, invoke, subscribe, unsubscribe } from "./reducer";
+import {
+	applyServerMessage,
+	getSurfaceSpec,
+	initialState,
+	invoke,
+	subscribe,
+	unsubscribe,
+} from "./reducer";
 
 const makeSpec = (id: string, title = id) => ({
 	id,
@@ -32,11 +39,10 @@ describe("applyServerMessage — catalog", () => {
 describe("applyServerMessage — surface", () => {
 	it("sets the spec for a subscribed surface", () => {
 		let s = initialState();
-		const result = subscribe(s, "s1");
-		s = result.state;
+		s = subscribe(s, "s1").state;
 		const spec = makeSpec("s1", "Surface 1");
 		const next = applyServerMessage(s, { type: "surface", spec });
-		expect(next.subscriptions.get("s1")).toEqual(spec);
+		expect(getSurfaceSpec(next, "s1")).toEqual(spec);
 	});
 
 	it("ignores a surface message for a non-subscribed surface", () => {
@@ -56,7 +62,7 @@ describe("applyServerMessage — update", () => {
 			type: "update",
 			update: { surfaceId: "s1", spec: makeSpec("s1", "V2") },
 		});
-		expect(next.subscriptions.get("s1")?.title).toBe("V2");
+		expect(getSurfaceSpec(next, "s1")?.title).toBe("V2");
 	});
 
 	it("ignores an update for a non-subscribed surface", () => {
@@ -86,7 +92,7 @@ describe("applyServerMessage — error", () => {
 });
 
 describe("subscribe", () => {
-	it("emits exactly one subscribe message", () => {
+	it("emits exactly one subscribe message (global, no conversationId)", () => {
 		const s = initialState();
 		const result = subscribe(s, "s1");
 		expect(result.outgoing).toEqual([{ type: "subscribe", surfaceId: "s1" }]);
@@ -96,10 +102,14 @@ describe("subscribe", () => {
 	it("adds the surface to subscriptions with null spec", () => {
 		const s = initialState();
 		const result = subscribe(s, "s1");
-		expect(result.state.subscriptions.get("s1")).toBeNull();
+		expect(result.state.subscriptions.get("s1")).toEqual({
+			conversationId: undefined,
+			spec: null,
+		});
+		expect(getSurfaceSpec(result.state, "s1")).toBeNull();
 	});
 
-	it("is idempotent — second subscribe is a no-op", () => {
+	it("is idempotent — second subscribe with the same scope is a no-op", () => {
 		let s = initialState();
 		s = subscribe(s, "s1").state;
 		const result = subscribe(s, "s1");
@@ -108,6 +118,67 @@ describe("subscribe", () => {
 	});
 });
 
+describe("subscribe — conversation-scoped", () => {
+	it("includes conversationId in the subscribe message", () => {
+		const s = initialState();
+		const result = subscribe(s, "cache-warming", "conv-A");
+		expect(result.outgoing).toEqual([
+			{ type: "subscribe", surfaceId: "cache-warming", conversationId: "conv-A" },
+		]);
+		expect(result.state.subscriptions.get("cache-warming")?.conversationId).toBe("conv-A");
+	});
+
+	it("re-scopes on conversation switch: unsubscribe old pair then subscribe new", () => {
+		let s = initialState();
+		s = subscribe(s, "cw", "conv-A").state;
+		s = applyServerMessage(s, {
+			type: "surface",
+			spec: makeSpec("cw", "A-spec"),
+			conversationId: "conv-A",
+		});
+		const result = subscribe(s, "cw", "conv-B");
+		expect(result.outgoing).toEqual([
+			{ type: "unsubscribe", surfaceId: "cw", conversationId: "conv-A" },
+			{ type: "subscribe", surfaceId: "cw", conversationId: "conv-B" },
+		]);
+		// previous spec retained until the new one arrives (no flicker)
+		expect(getSurfaceSpec(result.state, "cw")?.title).toBe("A-spec");
+		expect(result.state.subscriptions.get("cw")?.conversationId).toBe("conv-B");
+	});
+
+	it("drops a stale update echoing the previous conversationId", () => {
+		let s = initialState();
+		s = subscribe(s, "cw", "conv-A").state;
+		s = subscribe(s, "cw", "conv-B").state; // re-scoped to B
+		const next = applyServerMessage(s, {
+			type: "update",
+			update: { surfaceId: "cw", spec: makeSpec("cw", "STALE-A"), conversationId: "conv-A" },
+		});
+		expect(getSurfaceSpec(next, "cw")).toBeNull(); // stale ignored, no spec yet for B
+	});
+
+	it("accepts an update echoing the current conversationId", () => {
+		let s = initialState();
+		s = subscribe(s, "cw", "conv-B").state;
+		const next = applyServerMessage(s, {
+			type: "update",
+			update: { surfaceId: "cw", spec: makeSpec("cw", "B-spec"), conversationId: "conv-B" },
+		});
+		expect(getSurfaceSpec(next, "cw")?.title).toBe("B-spec");
+	});
+
+	it("accepts a global (no-echo) surface message even when subscribed with a conversationId", () => {
+		// loaded-extensions is global: server ignores our conversationId and echoes none.
+		let s = initialState();
+		s = subscribe(s, "loaded-extensions", "conv-A").state;
+		const next = applyServerMessage(s, {
+			type: "surface",
+			spec: makeSpec("loaded-extensions", "Ext"),
+		});
+		expect(getSurfaceSpec(next, "loaded-extensions")?.title).toBe("Ext");
+	});
+});
+
 describe("unsubscribe", () => {
 	it("emits unsubscribe and drops the spec", () => {
 		let s = initialState();
@@ -118,6 +189,15 @@ describe("unsubscribe", () => {
 		expect(result.state.subscriptions.has("s1")).toBe(false);
 	});
 
+	it("includes conversationId for a scoped subscription", () => {
+		let s = initialState();
+		s = subscribe(s, "cw", "conv-A").state;
+		const result = unsubscribe(s, "cw");
+		expect(result.outgoing).toEqual([
+			{ type: "unsubscribe", surfaceId: "cw", conversationId: "conv-A" },
+		]);
+	});
+
 	it("is a no-op if not subscribed", () => {
 		const s = initialState();
 		const result = unsubscribe(s, "nope");
@@ -143,6 +223,20 @@ describe("invoke", () => {
 		]);
 	});
 
+	it("includes conversationId when provided", () => {
+		const s = initialState();
+		const result = invoke(s, "cw", "cache-warming/set-interval", 120, "conv-A");
+		expect(result.outgoing).toEqual([
+			{
+				type: "invoke",
+				surfaceId: "cw",
+				actionId: "cache-warming/set-interval",
+				payload: 120,
+				conversationId: "conv-A",
+			},
+		]);
+	});
+
 	it("does not mutate state", () => {
 		const s = initialState();
 		const result = invoke(s, "s1", "a1");