Allow provider selection for gateway OAuth reads and logins (#59819)

## Why

Gateway OAuth reads and logins previously used only the current provider, preventing clients from authorizing another configured provider without changing the default.

## What changed

- Add optional `modelProvider` params to `account/gatewayOAuth/read` and `account/gatewayOAuth/login`, preserving current-provider behavior for omitted or null params and selectors.
- Validate explicit providers against current managed policy without changing the default or any thread's provider.
- Retain readiness state across providers and send `account/gatewayOAuth/changed` notifications for every configured provider sharing the changed credential.
- Update protocol schemas, TypeScript types, Python models, and documentation.

## Testing

Add coverage for non-default provider login, retained readiness when alternating providers, notifications for shared credentials without starting login, and legacy TypeScript request compatibility.

GitOrigin-RevId: cfd472c322b821fe36b8c133a8de774f4ba48534

sdk/python/src/openai_codex/generated/v2_all.py

@@ -1842,12 +1842,32 @@ class GatewayOAuthCancelResponse(BaseModel):
     )
 
 
+class GatewayOAuthLoginParams(BaseModel):
+    model_config = ConfigDict(
+        populate_by_name=True,
+    )
+    model_provider: Annotated[
+        str | None,
+        Field(alias="modelProvider", description="Defaults to the current provider when omitted."),
+    ] = None
+
+
 class GatewayOAuthLoginResponse(BaseModel):
     model_config = ConfigDict(
         populate_by_name=True,
     )
 
 
+class GatewayOAuthReadParams(BaseModel):
+    model_config = ConfigDict(
+        populate_by_name=True,
+    )
+    model_provider: Annotated[
+        str | None,
+        Field(alias="modelProvider", description="Defaults to the current provider when omitted."),
+    ] = None
+
+
 class GatewayOAuthStatus(Enum):
     not_ready = "notReady"
     started = "started"
@@ -3086,6 +3106,14 @@ class NonSteerableTurnKind(Enum):
     compact = "compact"
 
 
+class NullableGatewayOAuthLoginParams(RootModel[GatewayOAuthLoginParams | None]):
+    root: Annotated[GatewayOAuthLoginParams | None, Field(title="Nullable_GatewayOAuthLoginParams")]
+
+
+class NullableGatewayOAuthReadParams(RootModel[GatewayOAuthReadParams | None]):
+    root: Annotated[GatewayOAuthReadParams | None, Field(title="Nullable_GatewayOAuthReadParams")]
+
+
 class NullableGetAccountRateLimitsParams(RootModel[GetAccountRateLimitsParams | None]):
     root: Annotated[
         GetAccountRateLimitsParams | None, Field(title="Nullable_GetAccountRateLimitsParams")
@@ -7956,7 +7984,7 @@ class AccountGatewayOAuthReadRequest(BaseModel):
     method: Annotated[
         Literal["account/gatewayOAuth/read"], Field(title="Account/gatewayOAuth/readRequestMethod")
     ]
-    params: Annotated[None, Field(None)] = None
+    params: GatewayOAuthReadParams | None = None
 
 
 class AccountGatewayOAuthLoginRequest(BaseModel):
@@ -7968,7 +7996,7 @@ class AccountGatewayOAuthLoginRequest(BaseModel):
         Literal["account/gatewayOAuth/login"],
         Field(title="Account/gatewayOAuth/loginRequestMethod"),
     ]
-    params: Annotated[None, Field(None)] = None
+    params: GatewayOAuthLoginParams | None = None
 
 
 class AccountGatewayOAuthCancelRequest(BaseModel):