feat: enhance admin panel on book page — prompts, img2img, SSE chapter names

- Cover generation: editable prompt (pre-filled from title+summary),
  img2img toggle to use existing cover as reference, Full editor link
- Chapter cover: editable prompt textarea
- Description: instructions input field, Full editor link
- Chapter names: editable pattern field, SSE streaming with live batch
  progress, inline-editable title proposals, batch warning display

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

ui/src/routes/books/[slug]/+page.svelte

@@ -138,6 +138,21 @@
 	let coverPreview = $state<string | null>(null);
 	let coverSaving = $state(false);
 	let coverResult = $state<'saved' | 'error' | ''>('');
+	let coverPromptOpen = $state(false);
+
+	function buildCoverPrompt(): string {
+		const title = data.book?.title ?? '';
+		const summary = data.book?.summary ?? '';
+		const excerpt = summary.length > 200 ? summary.slice(0, 200) + '…' : summary;
+		return `Book cover art for "${title}"${excerpt ? ` — ${excerpt}` : ''}. Epic scene with dramatic lighting, professional book cover, highly detailed, 4K.`;
+	}
+
+	let coverPrompt = $state('');
+	let coverUseAsRef = $state(false);
+
+	$effect(() => {
+		if (coverPromptOpen && !coverPrompt) coverPrompt = buildCoverPrompt();
+	});
 
 	async function generateCover() {
 		const slug = data.book?.slug;
@@ -145,12 +160,34 @@
 		coverGenerating = true;
 		coverPreview = null;
 		coverResult = '';
+		const promptToUse = coverPrompt.trim() || buildCoverPrompt();
 		try {
-			const res = await fetch('/api/admin/image-gen', {
+			let res: Response;
-				method: 'POST',
+			if (coverUseAsRef && data.book?.cover) {
-				headers: { 'Content-Type': 'application/json' },
+				try {
-				body: JSON.stringify({ slug, type: 'cover', prompt: data.book?.title ?? slug })
+					const imgRes = await fetch(data.book.cover);
-			});
+					const blob = await imgRes.blob();
+					const ext = blob.type === 'image/jpeg' ? 'jpg' : blob.type === 'image/webp' ? 'webp' : 'png';
+					const file = new File([blob], `${slug}-cover-ref.${ext}`, { type: blob.type });
+					const fd = new FormData();
+					fd.append('json', JSON.stringify({ slug, type: 'cover', prompt: promptToUse, strength: 0.65 }));
+					fd.append('reference', file);
+					res = await fetch('/api/admin/image-gen', { method: 'POST', body: fd });
+				} catch {
+					// Fall back to text-only if cover fetch fails
+					res = await fetch('/api/admin/image-gen', {
+						method: 'POST',
+						headers: { 'Content-Type': 'application/json' },
+						body: JSON.stringify({ slug, type: 'cover', prompt: promptToUse })
+					});
+				}
+			} else {
+				res = await fetch('/api/admin/image-gen', {
+					method: 'POST',
+					headers: { 'Content-Type': 'application/json' },
+					body: JSON.stringify({ slug, type: 'cover', prompt: promptToUse })
+				});
+			}
 			if (res.ok) {
 				const d = await res.json();
 				coverPreview = d.image_b64 ? `data:${d.content_type ?? 'image/png'};base64,${d.image_b64}` : null;
@@ -195,6 +232,7 @@
 	let chapterCoverGenerating = $state(false);
 	let chapterCoverPreview = $state<string | null>(null);
 	let chapterCoverResult = $state<'error' | ''>('');
+	let chapterCoverPrompt = $state('');
 
 	async function generateChapterCover() {
 		const slug = data.book?.slug;
@@ -204,11 +242,12 @@
 		chapterCoverGenerating = true;
 		chapterCoverPreview = null;
 		chapterCoverResult = '';
+		const promptToUse = chapterCoverPrompt.trim() || `Chapter ${n} illustration for "${data.book?.title ?? slug}". Dramatic scene, vivid colors, detailed art, cinematic lighting.`;
 		try {
 			const res = await fetch('/api/admin/image-gen', {
 				method: 'POST',
 				headers: { 'Content-Type': 'application/json' },
-				body: JSON.stringify({ slug, type: 'chapter', chapter: n, prompt: data.book?.title ?? slug })
+				body: JSON.stringify({ slug, type: 'chapter', chapter: n, prompt: promptToUse })
 			});
 			if (res.ok) {
 				const d = await res.json();
@@ -228,6 +267,7 @@
 	let descPreview = $state('');
 	let descApplying = $state(false);
 	let descResult = $state<'applied' | 'error' | ''>('');
+	let descInstructions = $state('');
 
 	async function generateDesc() {
 		const slug = data.book?.slug;
@@ -239,7 +279,7 @@
 			const res = await fetch('/api/admin/text-gen/description', {
 				method: 'POST',
 				headers: { 'Content-Type': 'application/json' },
-				body: JSON.stringify({ slug })
+				body: JSON.stringify({ slug, instructions: descInstructions.trim() || undefined })
 			});
 			if (res.ok) {
 				const d = await res.json();
@@ -281,9 +321,12 @@
 
 	// ── Admin: chapter names generation ───────────────────────────────────────
 	let chapNamesGenerating = $state(false);
-	let chapNamesPreview = $state<{ number: number; old_title: string; new_title: string }[]>([]);
+	let chapNamesPreview = $state<{ number: number; old_title: string; new_title: string; edited: string }[]>([]);
 	let chapNamesApplying = $state(false);
 	let chapNamesResult = $state<'applied' | 'error' | ''>('');
+	let chapNamesPattern = $state('Chapter {n}: {scene}');
+	let chapNamesBatchProgress = $state('');
+	let chapNamesBatchWarnings = $state<string[]>([]);
 
 	async function generateChapNames() {
 		const slug = data.book?.slug;
@@ -291,18 +334,46 @@
 		chapNamesGenerating = true;
 		chapNamesPreview = [];
 		chapNamesResult = '';
+		chapNamesBatchProgress = '';
+		chapNamesBatchWarnings = [];
 		try {
 			const res = await fetch('/api/admin/text-gen/chapter-names', {
 				method: 'POST',
 				headers: { 'Content-Type': 'application/json' },
-				body: JSON.stringify({ slug, pattern: 'Chapter {n}: {scene}' })
+				body: JSON.stringify({ slug, pattern: chapNamesPattern.trim() || 'Chapter {n}: {scene}' })
 			});
-			if (res.ok) {
+			if (!res.ok) {
-				const d = await res.json();
-				chapNamesPreview = d.chapters ?? [];
-			} else {
 				chapNamesResult = 'error';
+				return;
 			}
+			// SSE streaming response
+			const reader = res.body!.getReader();
+			const decoder = new TextDecoder();
+			let buffer = '';
+			outer: while (true) {
+				const { value, done } = await reader.read();
+				if (done) break;
+				buffer += decoder.decode(value, { stream: true });
+				const lines = buffer.split('\n');
+				buffer = lines.pop() ?? '';
+				for (const line of lines) {
+					if (!line.startsWith('data: ')) continue;
+					const payload = line.slice(6).trim();
+					if (!payload) continue;
+					let evt: { batch?: number; total_batches?: number; chapters_done?: number; total_chapters?: number; chapters?: { number: number; old_title: string; new_title: string }[]; error?: string; done?: boolean };
+					try { evt = JSON.parse(payload); } catch { continue; }
+					if (evt.done) { chapNamesBatchProgress = `Done — ${evt.total_chapters ?? chapNamesPreview.length} chapters`; chapNamesGenerating = false; break outer; }
+					if (evt.error) {
+						chapNamesBatchWarnings = [...chapNamesBatchWarnings, `Batch ${evt.batch}/${evt.total_batches}: ${evt.error}`];
+					} else if (evt.chapters) {
+						chapNamesPreview = [...chapNamesPreview, ...evt.chapters.map((c) => ({ ...c, edited: c.new_title }))];
+					}
+					if (evt.batch != null && evt.total_batches != null) {
+						chapNamesBatchProgress = `Batch ${evt.batch}/${evt.total_batches} · ${evt.chapters_done ?? chapNamesPreview.length}/${evt.total_chapters ?? '?'}`;
+					}
+				}
+			}
+			if (chapNamesPreview.length === 0 && chapNamesBatchWarnings.length === 0) chapNamesResult = 'error';
 		} catch {
 			chapNamesResult = 'error';
 		} finally {
@@ -316,7 +387,7 @@
 		chapNamesApplying = true;
 		chapNamesResult = '';
 		try {
-			const chapters = chapNamesPreview.map((c) => ({ number: c.number, title: c.new_title }));
+			const chapters = chapNamesPreview.map((c) => ({ number: c.number, title: c.edited?.trim() || c.new_title }));
 			const res = await fetch('/api/admin/text-gen/chapter-names/apply', {
 				method: 'POST',
 				headers: { 'Content-Type': 'application/json' },
@@ -890,7 +961,32 @@
 
 				<!-- Book cover generation -->
 				<div class="flex flex-col gap-2">
-					<p class="text-xs font-medium text-(--color-muted) uppercase tracking-wide">{m.book_detail_admin_book_cover()}</p>
+					<div class="flex items-center justify-between">
+						<p class="text-xs font-medium text-(--color-muted) uppercase tracking-wide">{m.book_detail_admin_book_cover()}</p>
+						<div class="flex items-center gap-2">
+							<button
+								onclick={() => (coverPromptOpen = !coverPromptOpen)}
+								class="text-xs text-(--color-muted) hover:text-(--color-text) transition-colors"
+							>
+								{coverPromptOpen ? 'Hide prompt' : 'Edit prompt'}
+							</button>
+							<a href="/admin/image-gen" class="text-xs text-(--color-brand)/70 hover:text-(--color-brand) transition-colors">Full editor ↗</a>
+						</div>
+					</div>
+					{#if coverPromptOpen}
+						<textarea
+							bind:value={coverPrompt}
+							rows="3"
+							placeholder={buildCoverPrompt()}
+							class="w-full px-2 py-1.5 rounded bg-(--color-surface-3) border border-(--color-border) text-(--color-text) text-xs focus:outline-none focus:border-(--color-brand) resize-y"
+						></textarea>
+						{#if book.cover}
+							<label class="flex items-center gap-2 cursor-pointer select-none w-fit">
+								<input type="checkbox" bind:checked={coverUseAsRef} class="accent-(--color-brand)" />
+								<span class="text-xs text-(--color-muted)">Use current cover as reference (img2img)</span>
+							</label>
+						{/if}
+					{/if}
 					<div class="flex items-center gap-3 flex-wrap">
 						<button
 							onclick={generateCover}
@@ -903,7 +999,7 @@
 							{:else}
 								<svg class="w-3 h-3" fill="none" stroke="currentColor" viewBox="0 0 24 24"><path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M4 16l4.586-4.586a2 2 0 012.828 0L16 16m-2-2l1.586-1.586a2 2 0 012.828 0L20 14m-6-6h.01M6 20h12a2 2 0 002-2V6a2 2 0 00-2-2H6a2 2 0 00-2 2v12a2 2 0 002 2z"/></svg>
 							{/if}
-							{m.book_detail_admin_generate()}
+							{m.book_detail_admin_generate()}{coverUseAsRef ? ' (img2img)' : ''}
 						</button>
 						{#if coverResult === 'error'}
 							<span class="text-xs text-(--color-danger)">{m.common_error()}</span>
@@ -932,6 +1028,12 @@
 				<!-- Chapter cover generation -->
 				<div class="flex flex-col gap-2">
 					<p class="text-xs font-medium text-(--color-muted) uppercase tracking-wide">{m.book_detail_admin_chapter_cover()}</p>
+					<textarea
+						bind:value={chapterCoverPrompt}
+						rows="2"
+						placeholder="Chapter {chapterCoverN} illustration for "{data.book?.title}". Dramatic scene, vivid colors…"
+						class="w-full px-2 py-1.5 rounded bg-(--color-surface-3) border border-(--color-border) text-(--color-text) text-xs focus:outline-none focus:border-(--color-brand) resize-y"
+					></textarea>
 					<div class="flex items-end gap-3 flex-wrap">
 						<div class="flex flex-col gap-1">
 							<label for="ch-cover-n" class="text-xs text-(--color-muted)">{m.book_detail_admin_chapter_n()}</label>
@@ -973,7 +1075,16 @@
 
 				<!-- Description generation -->
 				<div class="flex flex-col gap-2">
-					<p class="text-xs font-medium text-(--color-muted) uppercase tracking-wide">{m.book_detail_admin_description()}</p>
+					<div class="flex items-center justify-between">
+						<p class="text-xs font-medium text-(--color-muted) uppercase tracking-wide">{m.book_detail_admin_description()}</p>
+						<a href="/admin/text-gen" class="text-xs text-(--color-brand)/70 hover:text-(--color-brand) transition-colors">Full editor ↗</a>
+					</div>
+					<input
+						type="text"
+						bind:value={descInstructions}
+						placeholder="e.g. 3-sentence blurb, avoid spoilers, dramatic tone"
+						class="w-full px-2 py-1.5 rounded bg-(--color-surface-3) border border-(--color-border) text-(--color-text) text-xs focus:outline-none focus:border-(--color-brand)"
+					/>
 					<div class="flex items-center gap-3 flex-wrap">
 						<button
 							onclick={generateDesc}
@@ -1019,6 +1130,12 @@
 				<!-- Chapter names generation -->
 				<div class="flex flex-col gap-2">
 					<p class="text-xs font-medium text-(--color-muted) uppercase tracking-wide">{m.book_detail_admin_chapter_names()}</p>
+					<input
+						type="text"
+						bind:value={chapNamesPattern}
+						placeholder="Chapter {n}: {scene}"
+						class="w-full px-2 py-1.5 rounded bg-(--color-surface-3) border border-(--color-border) text-(--color-text) text-xs focus:outline-none focus:border-(--color-brand)"
+					/>
 					<div class="flex items-center gap-3 flex-wrap">
 						<button
 							onclick={generateChapNames}
@@ -1033,18 +1150,30 @@
 							{/if}
 							{m.book_detail_admin_generate()}
 						</button>
+						{#if chapNamesBatchProgress && chapNamesGenerating}
+							<span class="text-xs text-(--color-muted)">{chapNamesBatchProgress}</span>
+						{/if}
 						{#if chapNamesResult === 'error'}
 							<span class="text-xs text-(--color-danger)">{m.common_error()}</span>
 						{:else if chapNamesResult === 'applied'}
-							<span class="text-xs text-green-400">{m.book_detail_admin_applied()} ({chapNamesPreview.length > 0 ? chapNamesPreview.length : ''})</span>
+							<span class="text-xs text-green-400">{m.book_detail_admin_applied()}</span>
 						{/if}
 					</div>
+					{#if chapNamesBatchWarnings.length > 0}
+						{#each chapNamesBatchWarnings as w}
+							<p class="text-xs text-amber-400">{w}</p>
+						{/each}
+					{/if}
 					{#if chapNamesPreview.length > 0}
 						<div class="flex flex-col gap-1.5 max-h-48 overflow-y-auto rounded border border-(--color-border) p-2 bg-(--color-surface-3)">
 							{#each chapNamesPreview as ch}
-								<div class="flex gap-2 text-xs">
+								<div class="flex gap-2 text-xs items-center">
 									<span class="text-(--color-muted) flex-shrink-0 w-6 text-right">{ch.number}.</span>
-									<span class="text-(--color-text) truncate">{ch.new_title}</span>
+									<input
+										type="text"
+										bind:value={ch.edited}
+										class="flex-1 min-w-0 bg-transparent border-b border-(--color-border) text-(--color-text) text-xs focus:outline-none focus:border-(--color-brand) py-0.5"
+									/>
 								</div>
 							{/each}
 						</div>
@@ -1057,7 +1186,7 @@
 							>
 								{chapNamesApplying ? m.book_detail_admin_applying() : m.book_detail_admin_apply()} ({chapNamesPreview.length})
 							</button>
-							<button onclick={() => (chapNamesPreview = [])} class="text-xs text-(--color-muted) hover:text-(--color-text) transition-colors">{m.book_detail_admin_discard()}</button>
+							<button onclick={() => { chapNamesPreview = []; chapNamesBatchProgress = ''; chapNamesBatchWarnings = []; }} class="text-xs text-(--color-muted) hover:text-(--color-text) transition-colors">{m.book_detail_admin_discard()}</button>
 						</div>
 					{/if}
 				</div>