perf(shell): add fragment mode for fast rApp tab switching

When switching rApps from the dropdown, TabCache now requests
?fragment=1 which returns a lightweight JSON payload (~200 bytes)
instead of re-rendering the full 2000-line shell HTML template.
This eliminates server-side shell rendering and client-side
DOMParser overhead. Also prefetches fragments on hover.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

server/index.ts

@@ -84,7 +84,7 @@ import { vnbModule } from "../modules/rvnb/mod";
 import { crowdsurfModule } from "../modules/crowdsurf/mod";
 import { spaces, createSpace, resolveCallerRole, roleAtLeast } from "./spaces";
 import type { SpaceRoleString } from "./spaces";
-import { renderShell, renderSubPageInfo, renderOnboarding } from "./shell";
+import { renderShell, renderSubPageInfo, renderOnboarding, setFragmentMode } from "./shell";
 import { renderOutputListPage } from "./output-list";
 import { renderMainLanding, renderSpaceDashboard } from "./landing";
 import { syncServer } from "./sync-instance";
@@ -2595,6 +2595,22 @@ for (const mod of getAllModules()) {
 			return next();
 		});
 	}
+	// Fragment mode: signal renderShell to return lightweight JSON instead of full shell HTML.
+	// Used by TabCache for fast tab switching — skips the entire 2000-line shell template.
+	app.use(`/:space/${mod.id}`, async (c, next) => {
+		if (c.req.method !== "GET" || !c.req.query("fragment")) return next();
+		// Set the global flag so renderShell returns JSON fragment
+		setFragmentMode(true);
+		await next();
+		// renderShell already returned JSON — fix the content-type header
+		if (c.res.headers.get("content-type")?.includes("text/html")) {
+			const body = await c.res.text();
+			c.res = new Response(body, {
+				status: c.res.status,
+				headers: { "content-type": "application/json" },
+			});
+		}
+	});
 	app.route(`/:space/${mod.id}`, mod.routes);
 	// Auto-mount browsable output list pages
 	if (mod.outputPaths) {

server/shell.ts

@@ -85,6 +85,54 @@ export function getSpaceShellMeta(spaceSlug: string): { enabledModules: string[]
 	};
 }
 
+/**
+ * Render a lightweight JSON fragment for tab-cache.
+ * Returns only the body HTML, title, scripts, and styles — no shell chrome.
+ * Used by TabCache's ?fragment=1 requests to avoid re-rendering the full 2000-line shell.
+ */
+export function renderFragment(opts: {
+	title: string;
+	body: string;
+	scripts?: string;
+	styles?: string;
+}): string {
+	// Parse script srcs from the scripts string
+	const scriptSrcs: string[] = [];
+	const scriptRe = /src="([^"]+)"/g;
+	let m: RegExpExecArray | null;
+	if (opts.scripts) {
+		while ((m = scriptRe.exec(opts.scripts)) !== null) {
+			scriptSrcs.push(m[1]);
+		}
+	}
+
+	// Parse stylesheet hrefs from the styles string
+	const styleSrcs: string[] = [];
+	const styleRe = /href="([^"]+)"/g;
+	if (opts.styles) {
+		while ((m = styleRe.exec(opts.styles)) !== null) {
+			styleSrcs.push(m[1]);
+		}
+	}
+
+	// Extract inline <style> content
+	const inlineStyles: string[] = [];
+	const inlineRe = /<style[^>]*>([\s\S]*?)<\/style>/g;
+	if (opts.styles) {
+		while ((m = inlineRe.exec(opts.styles)) !== null) {
+			if (m[1].trim()) inlineStyles.push(m[1]);
+		}
+	}
+
+	return JSON.stringify({
+		title: opts.title,
+		body: opts.body,
+		scripts: scriptSrcs,
+		styles: styleSrcs,
+		inlineStyles,
+	});
+}
+
 export interface ShellOptions {
 	/** Page <title> */
 	title: string;
@@ -112,6 +160,8 @@ export interface ShellOptions {
 	enabledModules?: string[] | null;
 	/** Whether this space has client-side encryption enabled */
 	spaceEncrypted?: boolean;
+	/** If true, return lightweight JSON fragment instead of full shell HTML */
+	fragment?: boolean;
 	/** Optional tab bar rendered below the subnav. */
 	tabs?: Array<{ id: string; label: string; icon?: string }>;
 	/** Active tab ID (matched from URL path by server). First tab if omitted. */
@@ -138,7 +188,23 @@ export function buildSpaceUrl(space: string, path: string, host?: string): strin
 	return `http://${h}/${space}${path}`;
 }
 
+/** Global flag set by middleware to signal fragment mode to renderShell. */
+let _fragmentMode = false;
+export function setFragmentMode(on: boolean) { _fragmentMode = on; }
+
 export function renderShell(opts: ShellOptions): string {
+	// Fragment mode: return lightweight JSON instead of full shell HTML.
+	// Triggered by middleware setting the flag, or by opts.fragment.
+	if (opts.fragment || _fragmentMode) {
+		_fragmentMode = false; // Reset after use
+		return renderFragment({
+			title: opts.title,
+			body: opts.body,
+			scripts: opts.scripts,
+			styles: opts.styles,
+		});
+	}
+
 	const {
 		title,
 		moduleId,

shared/components/rstack-app-switcher.ts

@@ -415,6 +415,20 @@ export class RStackAppSwitcher extends HTMLElement {
 		};
 		document.addEventListener("click", this.#outsideClickHandler);
 
+		// Prefetch module fragments on hover for faster tab switching.
+		// Uses low-priority fetch so it doesn't compete with user-initiated requests.
+		if ((window as any).__rspaceTabBar) {
+			this.#shadow.querySelectorAll("a.item").forEach((el) => {
+				el.addEventListener("mouseenter", () => {
+					const moduleId = (el as HTMLElement).dataset.id;
+					if (!moduleId || moduleId === current) return;
+					const space = this.#getSpaceSlug();
+					const href = `/${space}/${moduleId}?fragment=1`;
+					fetch(href, { priority: "low" } as RequestInit).catch(() => {});
+				}, { once: true });
+			});
+		}
+
 		// Intercept same-origin module links → dispatch event for tab system
 		// Only intercept when the shell tab system is active (window.__rspaceTabBar).
 		// On landing pages (rspace.online/, rspace.online/{moduleId}), let links

shared/tab-cache.ts

@@ -185,7 +185,6 @@ export class TabCache {
 		try {
 			const resolved = new URL(url, window.location.href);
 			if (resolved.origin !== window.location.origin) {
-				// Rewrite subdomain URL to path format: /{space}/{moduleId}
 				fetchUrl = `/${space}/${moduleId}`;
 			}
 		} catch {
@@ -196,7 +195,9 @@ export class TabCache {
 		const app = document.getElementById("app");
 		if (!app) { console.warn("[TabCache] fetchAndInject: no #app"); return false; }
 
-		console.log("[TabCache] fetchAndInject:", fetchUrl, "for", moduleId);
+		// Append ?fragment=1 for lightweight JSON response (no full shell re-render)
+		const fragmentUrl = fetchUrl + (fetchUrl.includes("?") ? "&" : "?") + "fragment=1";
+		console.log("[TabCache] fetchAndInject:", fragmentUrl, "for", moduleId);
 
 		// Show loading spinner
 		const loadingPane = document.createElement("div");
@@ -212,23 +213,33 @@ export class TabCache {
 		const timeoutId = setTimeout(() => controller.abort(), 15_000);
 
 		try {
-			const resp = await fetch(fetchUrl, {
+			const resp = await fetch(fragmentUrl, {
-				headers: { "Accept": "text/html" },
 				signal: controller.signal,
 			});
 			if (!resp.ok) {
 				clearTimeout(timeoutId);
-				console.warn("[TabCache] fetchAndInject: HTTP", resp.status, "for", fetchUrl);
+				console.warn("[TabCache] fetchAndInject: HTTP", resp.status, "for", fragmentUrl);
 				loadingPane.remove();
 				return false;
 			}
 
-			const html = await resp.text();
 			clearTimeout(timeoutId);
-			console.log("[TabCache] fetchAndInject: got", html.length, "bytes for", moduleId);
+			const ct = resp.headers.get("content-type") || "";
-			const content = this.extractContent(html);
+			let content: { body: string; title: string; scripts: string[]; styles: string[]; inlineStyles: string[] } | null;
+
+			if (ct.includes("application/json")) {
+				// Fast path: server returned pre-extracted JSON fragment
+				content = await resp.json();
+				console.log("[TabCache] fetchAndInject: got JSON fragment for", moduleId);
+			} else {
+				// Fallback: server returned full HTML (fragment middleware didn't match)
+				const html = await resp.text();
+				console.log("[TabCache] fetchAndInject: got", html.length, "bytes HTML (fallback) for", moduleId);
+				content = this.extractContent(html);
+			}
+
 			if (!content) {
-				console.warn("[TabCache] fetchAndInject: extractContent returned null for", moduleId, "— HTML has #app:", html.includes('id="app"'));
+				console.warn("[TabCache] fetchAndInject: no content extracted for", moduleId);
 				loadingPane.remove();
 				return false;
 			}