DatabaseSessionService stores non-ASCII text as \uXXXX escapes in TEXT JSON columns #7610

🔴 Required Information

Describe the Bug:
DatabaseSessionService stores non-ASCII text (e.g. Japanese) as \uXXXX escape sequences in JSON columns on databases that store JSON as TEXT (SQLite, MySQL, etc.). The cause is DynamicJSON.process_bind_param in src/google/adk/sessions/schemas/shared.py, which calls json.dumps(value) with the default ensure_ascii=True.

Steps to Reproduce:

1. Create DatabaseSessionService(db_url="sqlite+aiosqlite:///sessions.db").
2. Create a session and append an event whose text is こんにちは, or set a state value to こんにちは.
3. Check data in DB

Expected Behavior:
The text is stored as-is (こんにちは) so it is readable when inspecting the database.

Observed Behavior:
The text is stored as \u3053\u3093\u306b\u3061\u306f in the database.

Environment Details:

• ADK Version: 2.12.0
• Desktop OS: macOS
• Python Version: 3.13.7

Model Information:

• Are you using LiteLLM: N/A
• Which model is being used: N/A

🟡 Optional Information

Regression:
Not a regression; json.dumps has used the default.

Minimal Reproduction Code:
You can see escaped data in console.

import asyncio
import sqlite3

from google.adk.events import Event
from google.adk.sessions import DatabaseSessionService
from google.genai import types

DB_FILE = "sessions.db"


async def main():
  service = DatabaseSessionService(db_url=f"sqlite+aiosqlite:///{DB_FILE}")
  session = await service.create_session(
      app_name="app", user_id="user", state={"greeting": "こんにちは"}
  )

  await service.append_event(
      session,
      Event(
          author="user",
          content=types.Content(
              role="user", parts=[types.Part(text="こんにちは")]
          ),
      ),
  )

  # Read the raw column straight from SQLite.
  con = sqlite3.connect(DB_FILE)
  print("sessions.state   :", con.execute("select state from sessions").fetchone()[0])
  print("events.event_data:", con.execute("select event_data from events").fetchone()[0])


asyncio.run(main())

How often has this issue occurred?:

• Always (100%)