feat(chat): old-Dispatch composer layout — textarea + send + status bar

Restore the ergonomic composer from old Dispatch: an auto-resizing textarea
(1→7 lines) with a fixed-width Send button beside it, and a status bar BELOW
holding a status icon · context-window fill bar (escalating success/warning/
error color) · compact token count (current / limit · pct%).

The bar reuses the latest turn's contextSize as current usage and HARDCODES a
1,000,000-token window limit as a placeholder (real per-model limit is the next
backend ask). Absorbs the standalone ContextSizeBadge (removed). Pure helpers
computeContextUsage + formatCompactTokens added to core/metrics (tested).
540 tests green.

2 files changed, 139 insertions, 33 deletions

diff --git a/src/features/chat/ui/Composer.svelte b/src/features/chat/ui/Composer.svelte
index 3762340..24c2c19 100644
--- a/src/features/chat/ui/Composer.svelte
+++ b/src/features/chat/ui/Composer.svelte
@@ -1,7 +1,59 @@
 <script lang="ts">
-	let { onSend }: { onSend: (text: string) => void } = $props();
+	import { computeContextUsage, formatCompactTokens } from "../../../core/metrics";
+
+	// Placeholder context-window limit until the backend reports a real
+	// per-model max (see backend-handoff §3). Hardcoded to 1,000,000 tokens.
+	const MAX_CONTEXT = 1_000_000;
+	const MAX_LINES = 7;
+
+	let {
+		onSend,
+		contextSize = undefined,
+		status = "idle",
+	}: {
+		onSend: (text: string) => void;
+		// Current context occupancy (latest turn's contextSize), or `undefined`
+		// when unknown — the status bar then shows "— tokens", never 0%.
+		contextSize?: number | undefined;
+		// Coarse agent status for the status-bar icon.
+		status?: "idle" | "running" | "error";
+	} = $props();
 
 	let text = $state("");
+	let inputEl: HTMLTextAreaElement | undefined;
+
+	const hasText = $derived(text.trim().length > 0);
+	const usage = $derived(computeContextUsage(contextSize, MAX_CONTEXT));
+	const hasUsage = $derived(contextSize !== undefined);
+
+	// As the window fills, escalate color: calm → warning → danger.
+	function fillClass(pct: number): string {
+		if (pct >= 90) return "progress-error";
+		if (pct >= 70) return "progress-warning";
+		return "progress-success";
+	}
+
+	function resize(): void {
+		const el = inputEl;
+		if (!el) return;
+		el.style.height = "auto";
+		const style = getComputedStyle(el);
+		const lineHeight = Number.parseFloat(style.lineHeight) || 20;
+		const paddingY =
+			Number.parseFloat(style.paddingTop) + Number.parseFloat(style.paddingBottom);
+		const borderY =
+			Number.parseFloat(style.borderTopWidth) + Number.parseFloat(style.borderBottomWidth);
+		const maxHeight = lineHeight * MAX_LINES + paddingY + borderY;
+		const next = Math.min(el.scrollHeight, maxHeight);
+		el.style.height = `${next}px`;
+		el.style.overflowY = el.scrollHeight > maxHeight ? "auto" : "hidden";
+	}
+
+	// Re-run resize whenever the value changes (covers programmatic clears too).
+	$effect(() => {
+		void text;
+		resize();
+	});
 
 	function handleSubmit(): void {
 		const trimmed = text.trim();
@@ -18,16 +70,90 @@
 	}
 </script>
 
-<form class="flex gap-2 p-4" onsubmit={(e) => { e.preventDefault(); handleSubmit(); }}>
-	<textarea
-		class="textarea textarea-bordered flex-1"
-		bind:value={text}
-		onkeydown={handleKeydown}
-		placeholder="Type a message..."
-		rows="3"
-		aria-label="Message input"
-	></textarea>
-	<button class="btn btn-primary" type="submit" disabled={text.trim().length === 0}>
-		Send
-	</button>
+<form
+	class="flex flex-col"
+	onsubmit={(e) => {
+		e.preventDefault();
+		handleSubmit();
+	}}
+>
+	<!-- Top bar: expanding textarea + send button -->
+	<div class="flex items-end gap-2 px-4 pt-3 pb-2">
+		<textarea
+			bind:this={inputEl}
+			class="textarea textarea-bordered flex-1 resize-none leading-normal !min-h-0 h-auto"
+			bind:value={text}
+			onkeydown={handleKeydown}
+			placeholder="Type a message..."
+			rows="1"
+			aria-label="Message input"
+		></textarea>
+		<button class="btn btn-primary w-20 shrink-0" type="submit" disabled={!hasText}>
+			Send
+		</button>
+	</div>
+
+	<!-- Bottom status bar: status icon · context-window fill · token count -->
+	<div class="flex items-center gap-2 px-4 pb-2 text-xs text-base-content/50">
+		<span class="shrink-0">
+			{#if status === "running"}
+				<span class="loading loading-spinner loading-xs text-primary"></span>
+			{:else if status === "error"}
+				<svg
+					xmlns="http://www.w3.org/2000/svg"
+					viewBox="0 0 24 24"
+					fill="none"
+					stroke="currentColor"
+					stroke-width="2"
+					stroke-linecap="round"
+					stroke-linejoin="round"
+					class="h-4 w-4 text-error"
+					aria-label="Error"
+				>
+					<circle cx="12" cy="12" r="10"></circle>
+					<line x1="12" y1="8" x2="12" y2="12"></line>
+					<line x1="12" y1="16" x2="12.01" y2="16"></line>
+				</svg>
+			{:else}
+				<svg
+					xmlns="http://www.w3.org/2000/svg"
+					viewBox="0 0 24 24"
+					fill="none"
+					stroke="currentColor"
+					stroke-width="2.5"
+					stroke-linecap="round"
+					stroke-linejoin="round"
+					class="h-4 w-4 text-success"
+					aria-label="Idle"
+				>
+					<polyline points="20 6 9 17 4 12"></polyline>
+				</svg>
+			{/if}
+		</span>
+
+		{#if usage.percent !== null}
+			<progress
+				class="progress h-2 flex-1 {fillClass(usage.percent)}"
+				value={usage.percent}
+				max="100"
+			></progress>
+		{:else}
+			<progress class="progress h-2 flex-1 opacity-40" value="0" max="100"></progress>
+		{/if}
+
+		<span class="shrink-0 whitespace-nowrap font-mono">
+			{#if hasUsage}
+				{formatCompactTokens(usage.current)}{#if usage.max !== null}<span
+						class="text-base-content/40"
+					>
+						/ {formatCompactTokens(usage.max)}</span
+					>{/if}
+				{#if usage.percent !== null}
+					<span class="ml-1">· {usage.percent.toFixed(1)}%</span>
+				{/if}
+			{:else}
+				<span class="text-base-content/40">— tokens</span>
+			{/if}
+		</span>
+	</div>
 </form>
diff --git a/src/features/chat/ui/ContextSizeBadge.svelte b/src/features/chat/ui/ContextSizeBadge.svelte
deleted file mode 100644
index 475d54f..0000000
--- a/src/features/chat/ui/ContextSizeBadge.svelte
+++ /dev/null
@@ -1,20 +0,0 @@
-<script lang="ts">
-	import { formatContextSize } from "../../../core/metrics";
-
-	let {
-		contextSize,
-	}: {
-		// The conversation's current context size (tokens occupied), or `undefined`
-		// ("unknown") when no finalized turn has reported one yet. Never `0` for the
-		// unknown case — `formatContextSize` renders a placeholder instead.
-		contextSize: number | undefined;
-	} = $props();
-
-	const label = $derived(formatContextSize(contextSize));
-</script>
-
-<div class="px-4 pb-1 text-xs opacity-60" aria-live="polite">
-	<span title="The model's max context window is not reported yet — current usage only.">
-		{label}
-	</span>
-</div>