feat(openai): 支持messages模型映射与instructions模板注入

backend/internal/service/openai_codex_instructions_template.go

@@ -0,0 +1,55 @@
+package service
+
+import (
+	"bytes"
+	"fmt"
+	"strings"
+	"text/template"
+)
+
+type forcedCodexInstructionsTemplateData struct {
+	ExistingInstructions string
+	OriginalModel        string
+	NormalizedModel      string
+	BillingModel         string
+	UpstreamModel        string
+}
+
+func applyForcedCodexInstructionsTemplate(
+	reqBody map[string]any,
+	templateText string,
+	data forcedCodexInstructionsTemplateData,
+) (bool, error) {
+	rendered, err := renderForcedCodexInstructionsTemplate(templateText, data)
+	if err != nil {
+		return false, err
+	}
+	if rendered == "" {
+		return false, nil
+	}
+
+	existing, _ := reqBody["instructions"].(string)
+	if strings.TrimSpace(existing) == rendered {
+		return false, nil
+	}
+
+	reqBody["instructions"] = rendered
+	return true, nil
+}
+
+func renderForcedCodexInstructionsTemplate(
+	templateText string,
+	data forcedCodexInstructionsTemplateData,
+) (string, error) {
+	tmpl, err := template.New("forced_codex_instructions").Option("missingkey=zero").Parse(templateText)
+	if err != nil {
+		return "", fmt.Errorf("parse forced codex instructions template: %w", err)
+	}
+
+	var buf bytes.Buffer
+	if err := tmpl.Execute(&buf, data); err != nil {
+		return "", fmt.Errorf("render forced codex instructions template: %w", err)
+	}
+
+	return strings.TrimSpace(buf.String()), nil
+}