DatabaseSessionService.list_sessions lacks pagination support

[rusherman]

Description

DatabaseSessionService.list_sessions() queries all session rows for a given app_name (and optional user_id) without any pagination mechanism (LIMIT/OFFSET or cursor-based). When the number of sessions under an app grows large, this causes severe performance issues.

Impact

In our production environment with ~10k sessions per app, calling list_sessions() takes approximately 74 seconds to return, making the API endpoint essentially unusable.

Current Behavior

# base_session_service.py
class ListSessionsResponse(BaseModel):
    sessions: list[Session] = Field(default_factory=list)

async def list_sessions(
    self, *, app_name: str, user_id: Optional[str] = None
) -> ListSessionsResponse:
    ...

The method returns all sessions at once with no way to limit the result set.

Proposed Solution

Add pagination support to BaseSessionService.list_sessions() and DatabaseSessionService:

class ListSessionsResponse(BaseModel):
    sessions: list[Session] = Field(default_factory=list)
    next_page_token: str | None = None

async def list_sessions(
    self,
    *,
    app_name: str,
    user_id: str | None = None,
    page_size: int = 20,
    page_token: str | None = None,
) -> ListSessionsResponse:
    ...

The implementation should:

• Accept page_size (with a reasonable default, e.g. 20, max 100) and page_token
• Query with LIMIT/OFFSET (or cursor-based pagination)
• Order by update_time DESC for consistent results
• Return next_page_token when more results are available
• Maintain backward compatibility (default behavior returns first page)

Workaround

We currently bypass DatabaseSessionService.list_sessions() by querying PostgreSQL directly with LIMIT/OFFSET in our service layer.

Environment

• ADK version: 1.25.1
• Python: 3.12
• Database: PostgreSQL with asyncpg