配布済みアプリに残るモデル名と、停止日をまたいだ切り戻しの設計

struct AIRequest: Encodable {
    let capability: String   // "wallpaper.classify" のような機能名
    let assetId: String
    let locale: String
}
 
func classify(assetId: String) async throws -> Classification {
    var req = URLRequest(url: URL(string: "https://api.example.com/v1/ai")!)
    req.httpMethod = "POST"
    req.setValue("application/json", forHTTPHeaderField: "Content-Type")
    // クライアントのバージョンは送る。モデル名は送らない
    req.setValue(Bundle.main.appVersion, forHTTPHeaderField: "X-App-Version")
    req.httpBody = try JSONEncoder().encode(
        AIRequest(capability: "wallpaper.classify",
                  assetId: assetId,
                  locale: Locale.current.identifier)
    )
    let (data, resp) = try await URLSession.shared.data(for: req)
    guard let http = resp as? HTTPURLResponse, http.statusCode == 200 else {
        // 機能単位で静かに縮退する。ここで画面全体を落とさない
        throw AIError.unavailable
    }
    return try JSONDecoder().decode(Classification.self, from: data)
}

import os
from google import genai
 
client = genai.Client(api_key=os.environ["GEMINI_API_KEY"])
 
# モデル名が出てくるのは、このテーブルだけに限定する
CAPABILITY_MODELS = {
    "wallpaper.classify": "gemini-3.7-flash",
    "image.describe":     "gemini-3.7-flash",
    "image.generate":     "gemini-3.1-flash-image",
}
 
# 旧クライアントが送ってくるかもしれない機能名の読み替え
CAPABILITY_ALIASES = {
    "image.imagen4": "image.generate",   # v2.3.0 以前が送ってくる旧称
}
 
class UnknownCapability(Exception):
    pass
 
def resolve_model(capability: str) -> str:
    key = CAPABILITY_ALIASES.get(capability, capability)
    model = CAPABILITY_MODELS.get(key)
    if model is None:
        # 未知の機能名は落とす。推測して既定モデルに流すと事故が見えなくなる
        raise UnknownCapability(capability)
    return model
 
def run(capability: str, parts: list) -> str:
    model = resolve_model(capability)
    resp = client.models.generate_content(model=model, contents=parts)
    return resp.text

FORBIDDEN_FIELDS = ("model", "model_name", "engine")
 
def sanitize(payload: dict) -> dict:
    # 旧クライアントが送ってくるモデル指定は、黙って捨てるのではなく記録して捨てる
    leaked = [f for f in FORBIDDEN_FIELDS if f in payload]
    if leaked:
        logger.warning(
            "client sent model hint: fields=%s version=%s",
            leaked, payload.get("_app_version", "unknown"),
        )
        for f in leaked:
            payload.pop(f)
    return payload