DatabaseSessionService on PostgreSQL changes state values and can't store a NUL #7854

Describe the Bug:

Currently, DynamicJSON stores state and events as JSONB on PostgreSQL, so dict keys come back reordered, floats from 1e16 up come back as ints, -0.0 as 0.0, and text with a NUL is refused. The same service on SQLite stores json.dumps text and keeps every value.

Steps to Reproduce:

With google-adk[db] and psycopg[binary] installed, run this as python repro.py postgresql+psycopg://localhost/postgres and as python repro.py sqlite+aiosqlite:///a.db:

import asyncio, sys
from google.adk.events import Event, EventActions
from google.adk.sessions import DatabaseSessionService
from google.genai import types

async def main():
    svc = DatabaseSessionService(sys.argv[1])
    s = await svc.create_session(app_name="a", user_id="u")
    d = {"k": {"b": 1, "a": 2}, "x": 1e23, "z": -0.0}
    await svc.append_event(s, Event(author="a", actions=EventActions(state_delta=d)))
    s = await svc.get_session(app_name="a", user_id="u", session_id=s.id)

    print(s.state["k"], s.state["x"], s.state["z"])
    # PostgreSQL: {'a': 2, 'b': 1} 100000000000000000000000 0.0
    # SQLite:     {'b': 1, 'a': 2} 1e+23 -0.0
    # the float 1e23 is 99999999999999991611392, so the int is a different number

    t = types.Content(role="model", parts=[types.Part(text="a\x00b")])
    await svc.append_event(s, Event(author="a", content=t))
    # PostgreSQL: sqlalchemy.exc.DataError: (psycopg.errors.UntranslatableCharacter) unsupported Unicode escape sequence
    # SQLite:     no error

asyncio.run(main())

Expected Behavior:

On PostgreSQL the script prints the SQLite line and appends the event.

Observed Behavior:

The state comes back as the PostgreSQL: line shows, and the last append_event raises sqlalchemy.exc.DataError: (psycopg.errors.UntranslatableCharacter) unsupported Unicode escape sequence with DETAIL: \u0000 cannot be converted to text.

Environment Details:

• ADK Library Version (pip show google-adk): 2.13.0 and main
• Desktop OS: macOS 26.7.1, arm64 (Darwin 25.6.0)
• Python Version (python -V): Python 3.12.16
• PostgreSQL 18.6, SQLAlchemy 2.1.6, psycopg 3.3.6; asyncpg 0.32.0 gives the same state and the same NUL error

Model Information:

• Are you using LiteLLM: No
• Which model is being used: N/A

Additional Context:

Through a json column instead of jsonb, PostgreSQL returns the state dict and the NUL text unchanged.

How often has this issue occurred?:

• Always (100%)