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, 58 insertions, 0 deletions

diff --git a/src/features/markdown/logic/markdown.test.ts b/src/features/markdown/logic/markdown.test.ts
new file mode 100644
index 0000000..7dbb878
--- /dev/null
+++ b/src/features/markdown/logic/markdown.test.ts
@@ -0,0 +1,58 @@
+import { describe, expect, it } from "vitest";
+import { renderMarkdown } from "./markdown";
+
+describe("renderMarkdown", () => {
+	it("renders GFM markdown (headings, emphasis)", () => {
+		const html = renderMarkdown("# Title\n\nSome **bold** text.");
+		expect(html).toContain("<h1");
+		expect(html).toContain("Title");
+		expect(html).toContain("<strong>bold</strong>");
+	});
+
+	it("highlights fenced code for a known language", () => {
+		const html = renderMarkdown("```javascript\nconst x = 1;\n```");
+		expect(html).toContain("language-javascript");
+		expect(html).toContain("hljs-keyword"); // `const` got highlighted
+	});
+
+	it("resolves language aliases (js -> javascript)", () => {
+		const html = renderMarkdown("```js\nconst x = 1;\n```");
+		expect(html).toContain("hljs-keyword");
+	});
+
+	it("escapes code for an unknown language without throwing", () => {
+		const html = renderMarkdown("```nope\n<b>x</b>\n```");
+		expect(html).toContain("&lt;b&gt;");
+	});
+
+	it("sanitizes dangerous HTML", () => {
+		const html = renderMarkdown("Hi <script>alert(1)</script> there");
+		expect(html).not.toContain("<script>");
+		expect(html).toContain("Hi");
+	});
+
+	it("balances dangling bold emphasis while streaming", () => {
+		expect(renderMarkdown("a **bold", { streaming: true })).toContain("<strong>bold</strong>");
+	});
+
+	it("does not balance delimiters when not streaming", () => {
+		expect(renderMarkdown("a **bold")).not.toContain("<strong>");
+	});
+
+	it("wraps fenced code blocks with a copy button", () => {
+		const html = renderMarkdown("```js\nconst x = 1;\n```");
+		expect(html).toContain("code-block");
+		expect(html).toContain("data-copy");
+		expect(html).toContain("<pre>");
+	});
+
+	it("does not add a copy button to inline code", () => {
+		const html = renderMarkdown("use `npm run dev` please");
+		expect(html).not.toContain("data-copy");
+		expect(html).toContain("<code>npm run dev</code>");
+	});
+
+	it("returns an empty string for empty input", () => {
+		expect(renderMarkdown("")).toBe("");
+	});
+});