fix(security): harden password recovery with usable eight-character codes (#2477)

Use eight securely random recovery-code characters with concurrency-safe online throttling. Preserve existing keys and verify recovery through browser and real SQLite integration tests.

Co-authored-by: zhangjinpeng@mail.tuchong.com <zhangjinpeng@mail.tuchong.com>
Co-authored-by: dadachann <185672915+dadachann@users.noreply.github.com>

src/langbot/pkg/core/stages/genkeys.py

@@ -1,9 +1,18 @@
 from __future__ import annotations
 
+import logging
 import secrets
 
 from .. import stage, app
 
+# This stage runs before SetupLoggerStage, so ap.logger is still None here;
+# the module logger falls back to the stderr lastResort handler.
+_logger = logging.getLogger(__name__)
+
+# 32 symbols without 0/O or 1/I; eight independent draws provide 40 random bits.
+_RECOVERY_KEY_ALPHABET = '23456789ABCDEFGHJKLMNPQRSTUVWXYZ'
+_RECOVERY_KEY_LENGTH = 8
+
 
 @stage.stage_class('GenKeysStage')
 class GenKeysStage(stage.BootingStage):
@@ -20,5 +29,15 @@ class GenKeysStage(stage.BootingStage):
             ap.instance_config.data['system']['recovery_key'] = ''
 
         if not ap.instance_config.data['system']['recovery_key']:
-            ap.instance_config.data['system']['recovery_key'] = secrets.token_hex(3).upper()
+            # Keep recovery practical to type. Security also requires the reset
+            # endpoint's concurrency-safe quota (five admissions per 15 minutes).
+            ap.instance_config.data['system']['recovery_key'] = ''.join(
+                secrets.choice(_RECOVERY_KEY_ALPHABET) for _ in range(_RECOVERY_KEY_LENGTH)
+            )
             await ap.instance_config.dump_config()
+        elif len(ap.instance_config.data['system']['recovery_key']) < _RECOVERY_KEY_LENGTH:
+            _logger.warning(
+                'Low-entropy legacy recovery key detected (length < 8); '
+                'regenerate system.recovery_key in the configuration file '
+                'with a strong random value (#2392)'
+            )