fix: make session shard export deterministic

exportedAt used Date.now(), so the shard payload changed on every export
even when the session itself did not. git saw every shard as modified and
autoPushOnIdle produced a commit touching every session file on each idle.

Derive exportedAt from the session's own time_updated instead, so a repeat
export of an unchanged session is byte-identical and pushes stay incremental.

The existing regression test never caught this: under vitest the dynamic
import("node:sqlite") fails to resolve, sqliteAvailable() reported false
and every session test returned early. Fall back to createRequire so the
builtin loads under test runners and the session tests actually execute.

Refs #3

Author: aquelejota

src/core/sessions.ts

@@ -165,7 +165,10 @@ function buildShard(db: SqliteDatabase, sessionId: string, tables: string[]): Se
     formatVersion: 1,
     session: sessionRow,
     tables: {},
-    exportedAt: Date.now(),
+    // Derived from the session itself, never wall-clock time. A repeat export
+    // of an unchanged session must produce identical bytes, otherwise every
+    // push rewrites every shard and import/pull churn is unavoidable.
+    exportedAt: Number(sessionRow.time_updated ?? 0),
   };
 
   const projectId = sessionRow.project_id;

src/core/sqlite.ts

@@ -14,6 +14,8 @@
  * disabled with a clear message rather than failing halfway through.
  */
 
+import { createRequire } from "node:module";
+
 export interface SqliteStatement {
   all(...params: unknown[]): any[];
   run(...params: unknown[]): unknown;
@@ -39,6 +41,23 @@ async function importBunSqlite(): Promise<any> {
   return import(/* @vite-ignore */ /* webpackIgnore: true */ BUN_SQLITE);
 }
 
+/**
+ * Load the Node built-in SQLite driver.
+ *
+ * The plain dynamic import is what works under Node and Bun. Test runners such
+ * as vitest intercept dynamic imports and try to resolve `node:sqlite` as a
+ * project file, which makes the driver undetectable and silently turns every
+ * session test into an early return. `createRequire` bypasses the bundler and
+ * loads the real builtin, so those tests actually run.
+ */
+async function importNodeSqlite(): Promise<any> {
+  try {
+    return await import("node:sqlite");
+  } catch {
+    return createRequire(import.meta.url)("node:sqlite");
+  }
+}
+
 let cachedDriver: "bun" | "node" | "none" | undefined;
 
 async function detectDriver(): Promise<"bun" | "node" | "none"> {
@@ -53,7 +72,7 @@ async function detectDriver(): Promise<"bun" | "node" | "none"> {
     }
   }
   try {
-    const mod: any = await import("node:sqlite");
+    const mod: any = await importNodeSqlite();
     if (mod?.DatabaseSync) {
       cachedDriver = "node";
       return cachedDriver;
@@ -102,7 +121,7 @@ export async function openDatabase(
   }
 
   if (driver === "node") {
-    const { DatabaseSync } = (await import("node:sqlite")) as any;
+    const { DatabaseSync } = (await importNodeSqlite()) as any;
     const db = new DatabaseSync(file, options.readOnly ? { readOnly: true } : {});
     return {
       prepare: (sql: string) => {

tests/sessions.test.ts

@@ -305,13 +305,14 @@ describe("export and import", () => {
 
     await exportSessions(source, repo, { ...settings(), now }, silentReporter);
     const shard = path.join(repo, "_sessions", "ses_recent.json.gz");
-    const before = fs.statSync(shard).mtimeMs;
+    const before = fs.readFileSync(shard);
 
     await new Promise((resolve) => setTimeout(resolve, 20));
     await exportSessions(source, repo, { ...settings(), now }, silentReporter);
 
-    // An unchanged session must not produce a new diff on every push.
-    expect(fs.statSync(shard).mtimeMs).toBe(before);
+    // An unchanged session must not produce a new diff on every push — same
+    // bytes, same mtime, no diff for git to pick up.
+    expect(fs.readFileSync(shard).equals(before)).toBe(true);
   });
 });