feat: async chapter-names AI generation with review & apply

- Add POST /api/admin/text-gen/chapter-names/async backend endpoint: fire-and-forget,
  returns job_id immediately (HTTP 202), runs batch generation in background goroutine,
  persists proposed titles in ai_job payload when done
- Register new route in server.go alongside existing SSE endpoint (backward compat)
- Add SvelteKit proxy at /api/admin/text-gen/chapter-names/async
- Add SvelteKit proxy for GET /api/admin/ai-jobs/[id] (job detail with payload)
- Add Review button on ai-jobs page for done chapter-names jobs; inline panel shows
  editable title table (old to new) with Apply All button that POSTs to chapter-names/apply

backend/internal/backend/handlers_textgen.go

@@ -371,6 +371,215 @@ func parseChapterTitlesJSON(raw string) []rawChapterTitle {
 	return out
 }
 
+// handleAdminTextGenChapterNamesAsync handles POST /api/admin/text-gen/chapter-names/async.
+//
+// Fire-and-forget variant: validates inputs, creates an ai_job record, spawns a
+// background goroutine, and returns HTTP 202 with {job_id} immediately. The
+// goroutine runs all batches, stores the proposed titles in the job payload, and
+// marks the job done/failed/cancelled when finished.
+//
+// The client can poll GET /api/admin/ai-jobs/{id} for progress, then call
+// POST /api/admin/text-gen/chapter-names/apply once the job is "done".
+func (s *Server) handleAdminTextGenChapterNamesAsync(w http.ResponseWriter, r *http.Request) {
+	if s.deps.TextGen == nil {
+		jsonError(w, http.StatusServiceUnavailable, "text generation not configured (CFAI_ACCOUNT_ID/CFAI_API_TOKEN missing)")
+		return
+	}
+
+	var req textGenChapterNamesRequest
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		jsonError(w, http.StatusBadRequest, "parse body: "+err.Error())
+		return
+	}
+	if strings.TrimSpace(req.Slug) == "" {
+		jsonError(w, http.StatusBadRequest, "slug is required")
+		return
+	}
+	if strings.TrimSpace(req.Pattern) == "" {
+		jsonError(w, http.StatusBadRequest, "pattern is required")
+		return
+	}
+
+	// Load existing chapter list (use request context — just for validation).
+	allChapters, err := s.deps.BookReader.ListChapters(r.Context(), req.Slug)
+	if err != nil {
+		jsonError(w, http.StatusInternalServerError, "list chapters: "+err.Error())
+		return
+	}
+	if len(allChapters) == 0 {
+		jsonError(w, http.StatusNotFound, fmt.Sprintf("no chapters found for slug %q", req.Slug))
+		return
+	}
+
+	// Apply chapter range filter.
+	chapters := allChapters
+	if req.FromChapter > 0 || req.ToChapter > 0 {
+		filtered := chapters[:0]
+		for _, ch := range allChapters {
+			if req.FromChapter > 0 && ch.Number < req.FromChapter {
+				continue
+			}
+			if req.ToChapter > 0 && ch.Number > req.ToChapter {
+				break
+			}
+			filtered = append(filtered, ch)
+		}
+		chapters = filtered
+	}
+	if len(chapters) == 0 {
+		jsonError(w, http.StatusBadRequest, "no chapters in the specified range")
+		return
+	}
+
+	model := cfai.TextModel(req.Model)
+	if model == "" {
+		model = cfai.DefaultTextModel
+	}
+	maxTokens := req.MaxTokens
+	if maxTokens <= 0 {
+		maxTokens = 4096
+	}
+
+	// Index existing titles for old/new diff.
+	existing := make(map[int]string, len(chapters))
+	for _, ch := range chapters {
+		existing[ch.Number] = ch.Title
+	}
+
+	batches := chunkChapters(chapters, chapterNamesBatchSize)
+	totalBatches := len(batches)
+
+	if s.deps.AIJobStore == nil {
+		jsonError(w, http.StatusServiceUnavailable, "ai job store not configured")
+		return
+	}
+
+	jobPayload := fmt.Sprintf(`{"pattern":%q}`, req.Pattern)
+	jobID, createErr := s.deps.AIJobStore.CreateAIJob(r.Context(), domain.AIJob{
+		Kind:       "chapter-names",
+		Slug:       req.Slug,
+		Status:     domain.TaskStatusPending,
+		FromItem:   req.FromChapter,
+		ToItem:     req.ToChapter,
+		ItemsTotal: len(chapters),
+		Model:      string(model),
+		Payload:    jobPayload,
+		Started:    time.Now(),
+	})
+	if createErr != nil {
+		jsonError(w, http.StatusInternalServerError, "create ai job: "+createErr.Error())
+		return
+	}
+
+	jobCtx, jobCancel := context.WithCancel(context.Background())
+	registerCancelJob(jobID, jobCancel)
+
+	s.deps.Log.Info("admin: text-gen chapter-names async started",
+		"job_id", jobID, "slug", req.Slug,
+		"chapters", len(chapters), "batches", totalBatches, "model", model)
+
+	// Mark running before returning so the UI sees it immediately.
+	_ = s.deps.AIJobStore.UpdateAIJob(r.Context(), jobID, map[string]any{
+		"status": string(domain.TaskStatusRunning),
+	})
+
+	systemPrompt := `You are a chapter title editor for a web novel platform. ` +
+		`The user provides a list of chapter numbers with their current titles, ` +
+		`and a naming pattern template. ` +
+		`Your job: produce one new title for every chapter, following the pattern exactly. ` +
+		`Pattern placeholders: {n} = the chapter number (integer), {scene} = a very short (2–5 word) scene hint derived from the existing title. ` +
+		`RULES: ` +
+		`1. Do NOT include the chapter number inside the title text — the {n} placeholder is already in the pattern. ` +
+		`2. Do NOT include any prefix like "Chapter X -" or "Chapter X:" inside the title field itself. ` +
+		`3. The "title" field in your JSON must be the fully-rendered string (e.g. if pattern is "Chapter {n}: {scene}", output "Chapter 3: The Bet"). ` +
+		`4. Respond ONLY with a raw JSON array — no prose, no markdown fences, no explanation. ` +
+		`5. Each element: {"number": <int>, "title": <string>}. ` +
+		`6. Output every chapter in the input list, in order. Do not skip any.`
+
+	// Capture all locals needed in the goroutine.
+	store := s.deps.AIJobStore
+	textGen := s.deps.TextGen
+	logger := s.deps.Log
+	capturedModel := model
+	capturedMaxTokens := maxTokens
+	capturedPattern := req.Pattern
+	capturedSlug := req.Slug
+
+	go func() {
+		defer deregisterCancelJob(jobID)
+		defer jobCancel()
+
+		var allResults []proposedChapterTitle
+		chaptersDone := 0
+
+		for i, batch := range batches {
+			if jobCtx.Err() != nil {
+				_ = store.UpdateAIJob(context.Background(), jobID, map[string]any{
+					"status":   string(domain.TaskStatusCancelled),
+					"finished": time.Now().Format(time.RFC3339),
+				})
+				return
+			}
+
+			var chapterListSB strings.Builder
+			for _, ch := range batch {
+				chapterListSB.WriteString(fmt.Sprintf("%d: %s\n", ch.Number, ch.Title))
+			}
+			userPrompt := fmt.Sprintf("Naming pattern: %s\n\nChapters:\n%s", capturedPattern, chapterListSB.String())
+
+			raw, genErr := textGen.Generate(jobCtx, cfai.TextRequest{
+				Model: capturedModel,
+				Messages: []cfai.TextMessage{
+					{Role: "system", Content: systemPrompt},
+					{Role: "user", Content: userPrompt},
+				},
+				MaxTokens: capturedMaxTokens,
+			})
+			if genErr != nil {
+				logger.Error("admin: text-gen chapter-names async batch failed",
+					"job_id", jobID, "batch", i+1, "err", genErr)
+				// Continue — skip errored batch rather than aborting.
+				continue
+			}
+
+			proposed := parseChapterTitlesJSON(raw)
+			for _, p := range proposed {
+				allResults = append(allResults, proposedChapterTitle{
+					Number:   p.Number,
+					OldTitle: existing[p.Number],
+					NewTitle: p.Title,
+				})
+			}
+			chaptersDone += len(batch)
+
+			_ = store.UpdateAIJob(context.Background(), jobID, map[string]any{
+				"items_done": chaptersDone,
+			})
+		}
+
+		// Persist results into payload so the UI can load them for review.
+		resultsJSON, _ := json.Marshal(allResults)
+		finalPayload := fmt.Sprintf(`{"pattern":%q,"slug":%q,"results":%s}`,
+			capturedPattern, capturedSlug, string(resultsJSON))
+
+		status := domain.TaskStatusDone
+		if jobCtx.Err() != nil {
+			status = domain.TaskStatusCancelled
+		}
+		_ = store.UpdateAIJob(context.Background(), jobID, map[string]any{
+			"status":     string(status),
+			"items_done": chaptersDone,
+			"finished":   time.Now().Format(time.RFC3339),
+			"payload":    finalPayload,
+		})
+		logger.Info("admin: text-gen chapter-names async done",
+			"job_id", jobID, "slug", capturedSlug,
+			"results", len(allResults), "status", string(status))
+	}()
+
+	writeJSON(w, http.StatusAccepted, map[string]any{"job_id": jobID})
+}
+
 // ── Apply chapter names ───────────────────────────────────────────────────────
 
 // applyChapterNamesRequest is the JSON body for POST /api/admin/text-gen/chapter-names/apply.

backend/internal/backend/server.go

@@ -206,6 +206,7 @@ func (s *Server) ListenAndServe(ctx context.Context) error {
 	// Admin text generation endpoints (chapter names + book description)
 	mux.HandleFunc("GET /api/admin/text-gen/models", s.handleAdminTextGenModels)
 	mux.HandleFunc("POST /api/admin/text-gen/chapter-names", s.handleAdminTextGenChapterNames)
+	mux.HandleFunc("POST /api/admin/text-gen/chapter-names/async", s.handleAdminTextGenChapterNamesAsync)
 	mux.HandleFunc("POST /api/admin/text-gen/chapter-names/apply", s.handleAdminTextGenApplyChapterNames)
 	mux.HandleFunc("POST /api/admin/text-gen/description", s.handleAdminTextGenDescription)
 	mux.HandleFunc("POST /api/admin/text-gen/description/apply", s.handleAdminTextGenApplyDescription)