feat(server): memory v2 — BM25 + local embedding hybrid search

- Bm25Ranker: Okapi BM25 scoring (pure TS, no deps)
- Embedding module: ONNX-based local embeddings via onnxruntime-node
- Hybrid recall: BM25 (30%) + cosine similarity (70%) weighted merge
- Falls back to keyword-only via MEMORY_SEARCH=keyword env var
- extract_memory agent tool for persisting memory entries

apps/server/src/services/tools/extract_memory.ts

@@ -0,0 +1,44 @@
+import { z } from 'zod';
+import type { ToolDef } from '../tools/types.js';
+import { ensureMemoryScaffold, getMemoryRoot } from '../memory/paths.js';
+import { writeEntry } from '../memory/store.js';
+
+const ExtractMemoryInput = z.object({
+  topic: z.enum(['project', 'user', 'reference']).describe('Memory topic category'),
+  title: z.string().min(1).max(200).describe('Entry title (will be normalized to filename)'),
+  content: z.string().min(1).describe('Memory content body'),
+  tags: z.array(z.string()).optional().describe('Optional tags for search'),
+});
+
+type InputT = z.infer<typeof ExtractMemoryInput>;
+
+export const extractMemoryTool: ToolDef<InputT> = {
+  name: 'extract_memory',
+  description: 'Persist a memory entry to .boocode/memory/ for cross-session recall. Use for project conventions, user preferences, and architectural decisions.',
+  inputSchema: ExtractMemoryInput,
+  jsonSchema: {
+    type: 'function',
+    function: {
+      name: 'extract_memory',
+      description: 'Persist a memory entry for cross-session recall',
+      parameters: {
+        type: 'object',
+        properties: {
+          topic: { type: 'string', enum: ['project', 'user', 'reference'] },
+          title: { type: 'string', description: 'Entry title' },
+          content: { type: 'string', description: 'Memory content' },
+          tags: { type: 'array', items: { type: 'string' }, description: 'Search tags' },
+        },
+        required: ['topic', 'title', 'content'],
+      },
+    },
+  },
+  async execute(input: InputT, projectRoot: string): Promise<unknown> {
+    const root = getMemoryRoot(projectRoot);
+    await ensureMemoryScaffold(root);
+    await writeEntry(root, input.topic, input.title, input.content, input.tags ?? []);
+    return {
+      result: `Memory entry "${input.title}" saved to .boocode/memory/${input.topic}/`,
+    };
+  },
+};