CLI caches the E2E key (0600)

Argon2id ran on every CLI/MCP call; the derived key is now cached
owner-only in the data dir.

Todo: fda71ed1

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

lib/cli/cli_session.dart

@@ -7,6 +7,7 @@
 /// records hand-written into RTDB.
 library;
 
+import 'dart:convert';
 import 'dart:io';
 
 import 'package:crdt_sync/crdt_sync.dart';
@@ -149,6 +150,8 @@ class CliSession {
       store: _remote(push: push),
       oldPrefix: plainService.notesDir,
       readPassphrase: _readPassphrase,
+      // Argon2id once per install, not on every CLI/MCP call.
+      keyCache: E2eKeyCache(read: _readCachedKey, write: _writeCachedKey),
     );
     if (!push) {
       // Read-only during the migration: old builds still write the plaintext
@@ -181,6 +184,29 @@ class CliSession {
   RemoteStore _remote({required bool push}) =>
       push ? _firebase : PullOnlyStore(_firebase);
 
+  /// Owner-only file in the data dir caching the derived E2E key.
+  static const e2eKeyFileName = 'e2e_key';
+
+  File get _keyFile => File(p.join(dataDir, e2eKeyFileName));
+
+  Future<List<int>?> _readCachedKey() async {
+    final file = _keyFile;
+    if (!file.existsSync()) return null;
+    try {
+      return base64.decode((await file.readAsString()).trim());
+    } on FormatException {
+      return null;
+    }
+  }
+
+  Future<void> _writeCachedKey(List<int> bytes) async {
+    final file = _keyFile;
+    // Restrict before the key is written, never after.
+    await file.writeAsString('');
+    await Process.run('chmod', ['600', file.path]);
+    await file.writeAsString(base64.encode(bytes), flush: true);
+  }
+
   /// Environment variable holding the shared crdt-sync passphrase.
   static const e2ePassphraseEnv = 'TODO_E2E_PASSPHRASE';
 

pubspec.yaml

@@ -16,7 +16,7 @@ publish_to: 'none' # Remove this line if you wish to publish to pub.dev
 # https://developer.apple.com/library/archive/documentation/General/Reference/InfoPlistKeyReference/Articles/CoreFoundationKeys.html
 # In Windows, build-name is used as the major, minor, and patch parts
 # of the product and file versions while build-number is used as the build suffix.
-version: 1.0.86+1
+version: 1.0.87+1
 
 environment:
   sdk: ^3.12.2

test/cli/cli_session_test.dart

@@ -129,6 +129,21 @@ void main() {
       await session.close();
     });
 
+    test('the derived key is cached owner-only for the next run', () async {
+      final first = await open('cache');
+      await first.repository.upsert(note('n1'));
+      await first.sync(push: true);
+      await first.close();
+      final cached = File('${tmp.path}/cache/${CliSession.e2eKeyFileName}');
+      expect(cached.existsSync(), isTrue);
+      expect(cached.statSync().mode & 0x1ff, 384); // 0600
+      // Without any passphrase the next run still unlocks from the cache.
+      File('${tmp.path}/e2e_passphrase').deleteSync();
+      final second = await open('cache');
+      expect((await second.sync(push: true)).pushed, isFalse);
+      await second.close();
+    });
+
     test('a second node sees the first node note', () async {
       final a = await open('a');
       await a.repository.upsert(note('shared'));