feat: double write to all encrypted columns and decrypt on read (#5265)

* base

* use secret field

* fix

* auth code

* stage publish

* decouple backfill

* revert uncomment

* providers and agent vars

* mcp

* mcp

* stage and publish

* fix oauth

* double encrypt

* sandbox

---------

Co-authored-by: Letta Bot <noreply@letta.com>

tests/test_mcp_encryption.py

@@ -23,7 +23,7 @@ from letta.schemas.mcp import (
     SSEServerConfig,
     StdioServerConfig,
 )
-from letta.schemas.secret import Secret, SecretDict
+from letta.schemas.secret import Secret
 from letta.server.db import db_registry
 from letta.server.server import SyncServer
 from letta.services.mcp_manager import MCPManager