fix(mnemopi): align SQLite page size with OS page size

Add the initial page-size detection and regression coverage for file-backed Mnemopi databases.

packages/mnemopi/CHANGELOG.md

@@ -7,6 +7,9 @@
 ### Fixed
 
 - Stripped `<think>…</think>` reasoning blocks from remote LLM output in `cleanOutput`, so reasoning-model responses no longer leak into consolidated memories or corrupt fact extraction (the reasoning wrapper previously survived parsing and every stored fact became reasoning prose). ([#7231](https://github.com/can1357/oh-my-pi/issues/7231))
+### Fixed
+
+- Fixed SQLite databases being created with a hardcoded 4 KB page size regardless of the OS page size. On systems with larger pages (e.g. Apple Silicon / Asahi Linux at 16 KB), every SQLite page read touches 4 OS pages, causing 4x I/O amplification. Mnemopi now detects the OS page size at startup via `getconf PAGE_SIZE` and sets `PRAGMA page_size` before any tables are created, eliminating the write amplification on non-4K-page systems.
 
 ## [17.2.2] - 2026-07-31
 

packages/mnemopi/src/db.ts

@@ -3,6 +3,24 @@ import { mkdirSync } from "node:fs";
 import { dirname } from "node:path";
 import { dbPath } from "./config";
 
+let _osPageSize: number | undefined;
+
+function osPageSize(): number {
+	if (_osPageSize !== undefined) return _osPageSize;
+	try {
+		const proc = Bun.spawnSync(["getconf", "PAGE_SIZE"], { stdout: "pipe" });
+		if (proc.exitCode === 0) {
+			const size = Number.parseInt(proc.stdout.toString().trim(), 10);
+			if (size >= 512 && size <= 65536 && (size & (size - 1)) === 0) {
+				_osPageSize = size;
+				return size;
+			}
+		}
+	} catch { /* fall through */ }
+	_osPageSize = 4096;
+	return 4096;
+}
+
 export type DatabasePath = string | ":memory:";
 
 export interface OpenDatabaseOptions {
@@ -33,11 +51,14 @@ export function openDatabase(path: DatabasePath = dbPath(), options: OpenDatabas
 	if (options.loadExtension !== undefined) loadExtensions(db, options.loadExtension);
 	return db;
 }
-
 export function enablePragmas(db: Database, path?: DatabasePath): void {
 	db.exec("PRAGMA foreign_keys=ON");
 	db.exec("PRAGMA busy_timeout=5000");
-	if (path !== ":memory:") db.exec("PRAGMA journal_mode=WAL");
+	if (path !== ":memory:") {
+		const pageSize = osPageSize();
+		if (pageSize !== 4096) db.exec(`PRAGMA page_size=${pageSize}`);
+		db.exec("PRAGMA journal_mode=WAL");
+	}
 }
 
 export function loadExtensions(db: Database, extensions: string | readonly string[]): void {

packages/mnemopi/test/db-page-size.test.ts

@@ -0,0 +1,54 @@
+import { afterEach, describe, expect, it } from "bun:test";
+import { mkdtempSync, rmSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { openDatabase, closeQuietly } from "../src/db";
+
+function expectedOsPageSize(): number {
+	try {
+		const proc = Bun.spawnSync(["getconf", "PAGE_SIZE"], { stdout: "pipe" });
+		if (proc.exitCode === 0) {
+			const size = Number.parseInt(proc.stdout.toString().trim(), 10);
+			if (size >= 512 && size <= 65536 && (size & (size - 1)) === 0) return size;
+		}
+	} catch { /* fall through */ }
+	return 4096;
+}
+
+const roots: string[] = [];
+
+afterEach(() => {
+	for (;;) {
+		const root = roots.pop();
+		if (root === undefined) break;
+		rmSync(root, { recursive: true, force: true });
+	}
+});
+
+describe("db page size", () => {
+	it("creates a new database with page size matching the OS page size", () => {
+		const root = mkdtempSync(join(tmpdir(), "mnemopi-page-size-"));
+		roots.push(root);
+		const path = join(root, "test.db");
+
+		const db = openDatabase(path);
+		try {
+			const pageSize = db.query("PRAGMA page_size").get() as { page_size: number };
+			expect(pageSize.page_size).toBe(expectedOsPageSize());
+		} finally {
+			closeQuietly(db);
+		}
+	});
+
+	it("does not set page_size on in-memory databases", () => {
+		const db = openDatabase(":memory:");
+		try {
+			const pageSize = db.query("PRAGMA page_size").get() as { page_size: number };
+			// In-memory DBs keep the SQLite default (4096) since there is no
+			// persistent file whose I/O would benefit from OS page alignment.
+			expect(pageSize.page_size).toBe(4096);
+		} finally {
+			closeQuietly(db);
+		}
+	});
+});