feat(palace): add LLM memory extractor with regex fallback

backend/src/modules/palace/extractor.ts

@@ -0,0 +1,73 @@
+import {
+  buildExtractionPrompt,
+  parseExtractionResponse,
+  regexFallbackExtraction,
+  hallFromLabel,
+  HALL_PRESETS,
+} from '@bytelyst/palace';
+import type { ExtractedMemory } from '@bytelyst/palace';
+import { llm } from '../../lib/llm.js';
+import { config } from '../../lib/config.js';
+import { HALL_TYPES } from './types.js';
+import type { HallType } from './types.js';
+
+export type { ExtractedMemory };
+
+const NOTELETT_HALLS = HALL_PRESETS.notelett?.halls ?? HALL_TYPES;
+
+export interface NoteLettExtractedMemory {
+  hall: HallType;
+  content: string;
+  roomSlug: string;
+  entities: string[];
+}
+
+/**
+ * Extract memories from note content using LLM with regex fallback.
+ *
+ * Uses @bytelyst/palace shared extraction prompt builder + parser.
+ * Falls back to regex extraction if LLM is unavailable or fails.
+ */
+export async function extractMemories(
+  noteBody: string,
+  noteTitle: string,
+  workspaceName: string,
+): Promise<NoteLettExtractedMemory[]> {
+  if (!config.PALACE_EXTRACTION_ENABLED) return [];
+  if (!noteBody || noteBody.trim().length === 0) return [];
+
+  const content = noteBody.slice(0, 6000);
+  const prompt = buildExtractionPrompt(content, {
+    title: noteTitle,
+    context: workspaceName,
+    hallTypes: NOTELETT_HALLS,
+  });
+
+  let rawMemories: ExtractedMemory[];
+
+  try {
+    const provider = llm();
+    const result = await provider.chatCompletion({
+      model: config.LLM_DEFAULT_MODEL,
+      messages: [{ role: 'user', content: prompt }],
+      temperature: 0.1,
+    });
+    rawMemories = parseExtractionResponse(result.content);
+  } catch {
+    rawMemories = regexFallbackExtraction(content);
+  }
+
+  // Map to NoteLett halls, filtering out any that don't match
+  return rawMemories
+    .map(mem => {
+      const mappedHall = hallFromLabel(mem.hall, NOTELETT_HALLS as unknown as HallType[]) as HallType | undefined;
+      if (!mappedHall) return null;
+      return {
+        hall: mappedHall,
+        content: mem.content,
+        roomSlug: mem.roomSlug || 'general',
+        entities: mem.entities || [],
+      };
+    })
+    .filter((m): m is NoteLettExtractedMemory => m !== null);
+}