feat: playground multi-tab (Velxio/Flowchart/Circuit/Code) with auto-save

frontend/src/routes/playground/+page.svelte

@@ -1,12 +1,23 @@
 <script lang="ts">
 	import { onMount, onDestroy } from 'svelte';
 	import DeployFAB from '$components/DeployFAB.svelte';
+	import CircuitEditor from '$components/CircuitEditor.svelte';
+	import CodeEditor from '$components/CodeEditor.svelte';
+	import FlowchartTab from '../lesson/[slug]/FlowchartTab.svelte';
 
+	type PlaygroundTab = 'velxio' | 'flowchart' | 'circuit' | 'code';
+
+	let activeTab = $state<PlaygroundTab>('velxio');
+	let codeLanguage = $state<'c' | 'python'>('c');
+	let codeEditor = $state<CodeEditor | null>(null);
+	let currentCode = $state('');
+
+	// ── Velxio + DeployFAB ──
 	let velxioIframe = $state<HTMLIFrameElement | null>(null);
 	type DeployFABHandle = { setHex: (hex: string | null) => void };
 	let fabComponent = $state<DeployFABHandle | null>(null);
 
-	const iframeSrc = '/velxio/editor?embed=true&desktopLayout=true';
+	const velxioSrc = '/velxio/editor?embed=true&desktopLayout=true';
 
 	function handleMessage(e: MessageEvent) {
 		if (!e.data?.type) return;
@@ -32,6 +43,14 @@
 		velxioIframe?.contentWindow?.postMessage({ type: 'elemes:stop_hardware_serial' }, window.location.origin);
 	}
 
+	// ── Storage keys ──
+	const FLOWCHART_KEY = 'playground_flowchart_draft';
+	const CIRCUIT_KEY = 'playground_circuit_draft';
+	const CODE_C_KEY = 'playground_code_c_draft';
+	const CODE_PY_KEY = 'playground_code_python_draft';
+
+	let codeStorageKey = $derived(codeLanguage === 'python' ? CODE_PY_KEY : CODE_C_KEY);
+
 	onMount(() => {
 		window.addEventListener('message', handleMessage);
 	});
@@ -42,56 +61,189 @@
 </script>
 
 <svelte:head>
-	<title>Developer Playground — Velxio</title>
+	<title>Developer Playground — Elemes</title>
 </svelte:head>
 
 <div class="playground-page">
-	<iframe
+	<!-- Tab bar -->
-		bind:this={velxioIframe}
+	<div class="pg-tabs">
-		src={iframeSrc}
+		<button class="pg-tab" class:active={activeTab === 'velxio'} onclick={() => activeTab = 'velxio'}>
-		title="Velxio Editor"
+			Arduino
-		allow="bluetooth; clipboard-read; clipboard-write; fullscreen"
+		</button>
-		class="velxio-iframe"
+		<button class="pg-tab" class:active={activeTab === 'flowchart'} onclick={() => activeTab = 'flowchart'}>
-		allowfullscreen
+			Flowchart
-	></iframe>
+		</button>
+		<button class="pg-tab" class:active={activeTab === 'circuit'} onclick={() => activeTab = 'circuit'}>
+			Circuit
+		</button>
+		<div class="pg-tab-group">
+			<button class="pg-tab pg-tab-sub" class:active={activeTab === 'code' && codeLanguage === 'c'} onclick={() => { activeTab = 'code'; codeLanguage = 'c'; }}>
+				C
+			</button>
+			<button class="pg-tab pg-tab-sub" class:active={activeTab === 'code' && codeLanguage === 'python'} onclick={() => { activeTab = 'code'; codeLanguage = 'python'; }}>
+				Python
+			</button>
+		</div>
+	</div>
 
-	<DeployFAB
+	<!-- Content area -->
-		bind:this={fabComponent}
+	<div class="pg-content">
-		{velxioIframe}
+		{#if activeTab === 'velxio'}
-		onPushSerial={pushSerialToIframe}
+			<iframe
-		onSerialStart={notifySerialStart}
+				bind:this={velxioIframe}
-		onStopSerial={notifySerialStop}
+				src={velxioSrc}
-	/>
+				title="Velxio Editor"
+				allow="bluetooth; clipboard-read; clipboard-write; fullscreen"
+				class="pg-iframe"
+				allowfullscreen
+			></iframe>
+		{:else if activeTab === 'flowchart'}
+			<FlowchartTab
+				storageKey={FLOWCHART_KEY}
+			/>
+		{:else if activeTab === 'circuit'}
+			<div class="pg-circuit-wrap">
+				<CircuitEditor
+					storageKey={CIRCUIT_KEY}
+				/>
+			</div>
+		{:else if activeTab === 'code'}
+			<div class="pg-code-wrap">
+				{#key codeLanguage}
+				<CodeEditor
+					bind:this={codeEditor}
+					code={currentCode}
+					language={codeLanguage}
+					storageKey={codeStorageKey}
+					onchange={(val) => currentCode = val}
+				/>
+				{/key}
+			</div>
+		{/if}
+	</div>
+
+	<!-- DeployFAB only on Velxio tab -->
+	{#if activeTab === 'velxio'}
+		<DeployFAB
+			bind:this={fabComponent}
+			{velxioIframe}
+			onPushSerial={pushSerialToIframe}
+			onSerialStart={notifySerialStart}
+			onStopSerial={notifySerialStop}
+		/>
+	{/if}
 </div>
 
 <style>
 	.playground-page {
 		width: 100%;
 		height: 100dvh;
-		overflow-y: auto;
+		overflow: hidden;
-		overflow-x: hidden;
 		display: flex;
 		flex-direction: column;
 	}
 
-	.velxio-iframe {
+	/* ── Tab bar ── */
-		width: 100%;
+	.pg-tabs {
-		flex: 1;
+		display: flex;
-		min-height: 0;           /* critical: allows flex child to shrink below content size */
+		align-items: flex-end;
-		border: none;
+		gap: 2px;
-		display: block;
+		padding: 0 8px;
-		touch-action: pan-y;     /* allow vertical pan inside iframe */
+		background: var(--color-bg-secondary);
+		border-bottom: 1px solid var(--color-border);
+		min-height: 36px;
+		flex-shrink: 0;
 	}
 
+	.pg-tab {
+		padding: 5px 16px;
+		border: 1px solid transparent;
+		border-bottom: none;
+		border-radius: 8px 8px 0 0;
+		background: transparent;
+		color: var(--color-text-muted);
+		font-size: 0.78rem;
+		font-weight: 500;
+		cursor: pointer;
+		white-space: nowrap;
+		flex-shrink: 0;
+		margin-bottom: -1px;
+		z-index: 0;
+		transition: background 0.15s, color 0.15s;
+	}
+
+	.pg-tab:hover:not(.active) {
+		background: var(--color-border);
+		color: var(--color-text);
+	}
+
+	.pg-tab.active {
+		background: var(--color-bg);
+		color: var(--color-text);
+		font-weight: 600;
+		border-color: var(--color-border);
+		z-index: 1;
+	}
+
+	.pg-tab-group {
+		display: flex;
+		gap: 0;
+		align-items: flex-end;
+	}
+
+	.pg-tab-sub {
+		padding: 5px 12px;
+	}
+
+	/* ── Content area ── */
+	.pg-content {
+		flex: 1;
+		min-height: 0;
+		overflow: hidden;
+		display: flex;
+	}
+
+	.pg-iframe {
+		width: 100%;
+		flex: 1;
+		border: none;
+		display: block;
+		min-height: 0;
+	}
+
+	.pg-circuit-wrap {
+		width: 100%;
+		height: 100%;
+		overflow: auto;
+		padding: 8px;
+	}
+
+	.pg-code-wrap {
+		width: 100%;
+		height: 100%;
+		overflow: hidden;
+		display: flex;
+		flex-direction: column;
+	}
+
+	/* ── FlowchartTab fill ── */
+	.pg-content :global(.flowchart-container) {
+		flex: 1;
+		min-height: 0;
+	}
+
+	/* ── Mobile ── */
 	@media (max-width: 768px) {
 		.playground-page {
 			overflow-y: auto;
-			height: auto;        /* allow page to grow */
-			min-height: 100dvh;  /* but always at least fill viewport */
-		}
-		.velxio-iframe {
-			max-height: none;    /* iframe can grow taller than viewport */
 			height: auto;
+			min-height: 100dvh;
+		}
+		.pg-content {
+			min-height: 400px;
+		}
+		.pg-iframe {
+			min-height: 400px;
 		}
 	}
 </style>