fix fresh-host acceptance and document real-host debugging learnings

internal/host/sub2api/client.go

@@ -25,11 +25,12 @@ type HostAdapter interface {
 	CreateAccount(ctx context.Context, req CreateAccountRequest) (AccountRef, error)
 	BatchCreateAccounts(ctx context.Context, req BatchCreateAccountsRequest) ([]AccountRef, error)
 	DeleteAccount(ctx context.Context, accountID string) error
-	TestAccount(ctx context.Context, accountID string) (ProbeResult, error)
+	TestAccount(ctx context.Context, accountID, modelID string) (ProbeResult, error)
 	GetAccountModels(ctx context.Context, accountID string) ([]AccountModel, error)
 	EnsureSubscriptionAccess(ctx context.Context, req EnsureSubscriptionAccessRequest) (SubscriptionAccessRef, error)
 	AssignSubscription(ctx context.Context, req AssignSubscriptionRequest) (SubscriptionRef, error)
 	CheckGatewayAccess(ctx context.Context, req GatewayAccessCheckRequest) (GatewayAccessResult, error)
+	CheckGatewayCompletion(ctx context.Context, req GatewayCompletionCheckRequest) (GatewayCompletionResult, error)
 	ListManagedResources(ctx context.Context, req ListManagedResourcesRequest) (ManagedResourceSnapshot, error)
 }
 
@@ -159,6 +160,20 @@ type SubscriptionRef struct {
 	ID string `json:"id"`
 }
 
+type GatewayCompletionCheckRequest struct {
+	APIKey    string
+	Model     string
+	Prompt    string
+	MaxTokens int
+}
+
+type GatewayCompletionResult struct {
+	OK          bool   `json:"ok"`
+	StatusCode  int    `json:"status_code"`
+	ContentType string `json:"content_type,omitempty"`
+	BodyPreview string `json:"body_preview,omitempty"`
+}
+
 type Client struct {
 	baseURL     *url.URL
 	httpClient  *http.Client