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

internal/host/sub2api/gateway_probe.go

@@ -17,12 +17,16 @@ type GatewayAccessResult struct {
 	StatusCode       int      `json:"status_code"`
 	Models           []string `json:"models"`
 	HasExpectedModel bool     `json:"has_expected_model"`
+	CompletionOK     bool     `json:"completion_ok"`
+	CompletionStatus int      `json:"completion_status"`
+	CompletionType   string   `json:"completion_content_type,omitempty"`
+	CompletionBody   string   `json:"completion_body_preview,omitempty"`
 }
 
 func (c *Client) CheckGatewayAccess(ctx context.Context, req GatewayAccessCheckRequest) (GatewayAccessResult, error) {
 	gatewayClient := *c
-	gatewayClient.apiKey = strings.TrimSpace(req.APIKey)
-	gatewayClient.bearerToken = ""
+	gatewayClient.apiKey = ""
+	gatewayClient.bearerToken = strings.TrimSpace(req.APIKey)
 
 	statusCode, _, body, err := gatewayClient.perform(ctx, http.MethodGet, "/v1/models", nil)
 	if err != nil {
@@ -43,6 +47,44 @@ func (c *Client) CheckGatewayAccess(ctx context.Context, req GatewayAccessCheckR
 	return result, nil
 }
 
+func (c *Client) CheckGatewayCompletion(ctx context.Context, req GatewayCompletionCheckRequest) (GatewayCompletionResult, error) {
+	gatewayClient := *c
+	gatewayClient.apiKey = ""
+	gatewayClient.bearerToken = strings.TrimSpace(req.APIKey)
+
+	model := strings.TrimSpace(req.Model)
+	if model == "" {
+		return GatewayCompletionResult{}, nil
+	}
+	prompt := strings.TrimSpace(req.Prompt)
+	if prompt == "" {
+		prompt = "ping"
+	}
+	maxTokens := req.MaxTokens
+	if maxTokens <= 0 {
+		maxTokens = 8
+	}
+	payload := map[string]any{
+		"model": model,
+		"messages": []map[string]string{
+			{"role": "user", "content": prompt},
+		},
+		"max_tokens":  maxTokens,
+		"temperature": 0,
+	}
+
+	statusCode, headers, body, err := gatewayClient.perform(ctx, http.MethodPost, "/v1/chat/completions", payload)
+	if err != nil {
+		return GatewayCompletionResult{}, err
+	}
+	return GatewayCompletionResult{
+		OK:          statusCode >= http.StatusOK && statusCode < http.StatusMultipleChoices,
+		StatusCode:  statusCode,
+		ContentType: strings.TrimSpace(headers.Get("Content-Type")),
+		BodyPreview: previewGatewayBody(body, 400),
+	}, nil
+}
+
 func decodeGatewayModelIDs(body []byte) []string {
 	var payload struct {
 		Data []struct {
@@ -60,3 +102,11 @@ func decodeGatewayModelIDs(body []byte) []string {
 	}
 	return nil
 }
+
+func previewGatewayBody(body []byte, limit int) string {
+	trimmed := strings.TrimSpace(string(body))
+	if limit <= 0 || len(trimmed) <= limit {
+		return trimmed
+	}
+	return trimmed[:limit]
+}