Description

Create the data layer for RSS in diracx:

1. SQLAlchemy 2.0 models in diracx-db that map the existing ResourceStatusDB tables — no schema changes, DB is shared with legacy DIRAC.
2. Pydantic models in diracx-core for the consumer-facing view — a simplified binary allowed/banned model.

SQLAlchemy models

Note: The ResourceStatusCache table from the legacy schema is not needed — caching is handled by CacheableSource.

Technical details:

• Create diracx-db/src/diracx/db/sql/rss/ package with schema.py and db.py
• Follow diracx SQLAlchemy 2.0 patterns (DeclarativeBase, Mapped[T], mapped_column()) — see diracx-db/src/diracx/db/sql/auth/schema.py and job/schema.py for reference
• Create ResourceStatusDB(BaseSQLDB) with read methods for status queries
• Register via entry point in pyproject.toml under diracx.dbs.sql
• Must not create or alter tables — schema is owned by legacy DIRAC

Pydantic models

Implement the simplified binary consumer model proposed in the #790 discussion:

from pydantic import BaseModel
from typing import Literal

class AllowedStatus(BaseModel):
    allowed: Literal[True]
    warnings: list[str] = []

    def __bool__(self) -> bool:
        return True

class BannedStatus(BaseModel):
    allowed: Literal[False]
    reason: str = "Unknown"

    def __bool__(self) -> bool:
        return False

ResourceStatus = AllowedStatus | BannedStatus  # Discriminated union on `allowed`

class StorageElementStatus(BaseModel):
    read: ResourceStatus
    write: ResourceStatus
    check: ResourceStatus
    remove: ResourceStatus

class ComputeElementStatus(BaseModel):
    all: ResourceStatus

class SiteStatus(BaseModel):
    all: ResourceStatus

Mapping from DB status to binary model:

• Allowed: Active, Degraded
• Banned: Banned, Probing, Error, Unknown

This matches the existing getUsableSites logic in DIRAC (SiteStatus.py).

Reference

• Legacy schema: DIRAC/ResourceStatusSystem/DB/ResourceStatusDB.py (lines 86–260)
• Chris's model proposal: #790 comment
• Meeting agreement: all resource types (Storage, Compute, Site) implemented, binary allowed/banned for consumers

Acceptance criteria

• SQLAlchemy 2.0 models for the tables, matching the existing schema exactly
• ResourceStatusDB(BaseSQLDB) class with read methods for SiteStatus and ResourceStatus
• Entry point registered in pyproject.toml
• Pydantic models for AllowedStatus, BannedStatus, StorageElementStatus, ComputeElementStatus, SiteStatus
• ResourceType enum
• Unit tests for DB reads and model serialization/deserialization
• No DB migrations or schema changes