diff --git a/apps/api/internal/runner/param_processor.go b/apps/api/internal/runner/param_processor.go
index 3bf9550..8957575 100644
--- a/apps/api/internal/runner/param_processor.go
+++ b/apps/api/internal/runner/param_processor.go
@@ -11,6 +11,7 @@ import (
 )
 
 type paramProcessContext struct {
+	kind            string
 	modelCapability map[string]any
 	candidate       store.RuntimeModelCandidate
 	log             *parameterPreprocessingLog
@@ -58,6 +59,7 @@ func NewParamProcessorChain() ParamProcessorChain {
 		processors: []paramProcessor{
 			resolutionNormalizeProcessor{},
 			aspectRatioProcessor{},
+			messageContentProcessor{},
 			contentFilterProcessor{},
 			inputAudioProcessor{},
 			durationProcessor{},
@@ -91,6 +93,7 @@ func preprocessRequestWithLog(kind string, body map[string]any, candidate store.
 		},
 	}
 	context := &paramProcessContext{
+		kind:            kind,
 		modelCapability: effectiveModelCapability(candidate),
 		candidate:       candidate,
 		log:             &log,
@@ -333,6 +336,193 @@ func (aspectRatioProcessor) Process(params map[string]any, modelType string, con
 	return true
 }
 
+type messageContentProcessor struct{}
+
+func (messageContentProcessor) Name() string { return "MessageContentProcessor" }
+
+func (messageContentProcessor) ShouldProcess(params map[string]any, modelType string, context *paramProcessContext) bool {
+	return isTextGenerationKind(context.kind) && params["messages"] != nil
+}
+
+func (messageContentProcessor) Process(params map[string]any, modelType string, context *paramProcessContext) bool {
+	messages, changed := processMessageListContent(params["messages"], context)
+	if changed {
+		params["messages"] = messages
+	}
+	return true
+}
+
+func processMessageListContent(value any, context *paramProcessContext) ([]any, bool) {
+	rawMessages, ok := value.([]any)
+	if !ok {
+		return nil, false
+	}
+	out := make([]any, 0, len(rawMessages))
+	changed := false
+	for messageIndex, rawMessage := range rawMessages {
+		message, ok := rawMessage.(map[string]any)
+		if !ok {
+			out = append(out, rawMessage)
+			continue
+		}
+		nextMessage := cloneMap(message)
+		if contentParts, ok := message["content"].([]any); ok {
+			nextContent, contentChanged := processMessageContentParts(
+				contentParts,
+				fmt.Sprintf("messages[%d].content", messageIndex),
+				context,
+			)
+			if contentChanged {
+				nextMessage["content"] = nextContent
+				changed = true
+			}
+		}
+		out = append(out, nextMessage)
+	}
+	return out, changed
+}
+
+func processMessageContentParts(parts []any, basePath string, context *paramProcessContext) ([]any, bool) {
+	out := make([]any, 0, len(parts))
+	changed := false
+	for partIndex, rawPart := range parts {
+		part, ok := rawPart.(map[string]any)
+		if !ok {
+			out = append(out, rawPart)
+			continue
+		}
+		if replacement, replacementChanged := messageContentPartReplacement(part, context); replacementChanged {
+			out = append(out, replacement)
+			context.recordChange(
+				"MessageContentProcessor",
+				"convert",
+				fmt.Sprintf("%s[%d]", basePath, partIndex),
+				part,
+				replacement,
+				messageContentConversionReason(part),
+				messageContentCapabilityPath(part),
+				messageContentCapabilityValue(part, context),
+			)
+			changed = true
+			continue
+		}
+		out = append(out, cloneMap(part))
+	}
+	return out, changed
+}
+
+func messageContentPartReplacement(part map[string]any, context *paramProcessContext) (map[string]any, bool) {
+	switch {
+	case isImageContent(part):
+		if modelSupportsMessageModality(context, "image_analysis") {
+			return nil, false
+		}
+		if url := imageURLFromContentPart(part); url != "" {
+			return map[string]any{"type": "text", "text": "Image link: " + url}, true
+		}
+	case isVideoContent(part):
+		if modelSupportsMessageModality(context, "video_understanding") {
+			return nil, false
+		}
+		if url := videoURLFromContentPart(part); url != "" {
+			return map[string]any{"type": "text", "text": "video URL: " + url}, true
+		}
+	case isAudioContent(part) || stringFromAny(part["type"]) == "input_audio":
+		if modelSupportsMessageModality(context, "audio_understanding") {
+			return nil, false
+		}
+		if url := audioURLFromContentPart(part); url != "" {
+			return map[string]any{"type": "text", "text": "audio URL: " + url}, true
+		}
+	}
+	return nil, false
+}
+
+func messageContentConversionReason(part map[string]any) string {
+	switch {
+	case isImageContent(part):
+		return "模型不支持图像理解，已将 image_url 转为文本链接。"
+	case isVideoContent(part):
+		return "模型不支持视频理解，已将 video_url 转为文本链接。"
+	default:
+		return "模型不支持音频理解，已将音频输入转为文本链接。"
+	}
+}
+
+func messageContentCapabilityPath(part map[string]any) string {
+	switch {
+	case isImageContent(part):
+		return "capabilities.image_analysis"
+	case isVideoContent(part):
+		return "capabilities.video_understanding"
+	default:
+		return "capabilities.audio_understanding"
+	}
+}
+
+func messageContentCapabilityValue(part map[string]any, context *paramProcessContext) any {
+	if context == nil {
+		return nil
+	}
+	switch {
+	case isImageContent(part):
+		return capabilityValue(context.modelCapability, "image_analysis", "")
+	case isVideoContent(part):
+		return capabilityValue(context.modelCapability, "video_understanding", "")
+	default:
+		return capabilityValue(context.modelCapability, "audio_understanding", "")
+	}
+}
+
+func modelSupportsMessageModality(context *paramProcessContext, capabilityName string) bool {
+	if context == nil {
+		return false
+	}
+	capabilities := context.modelCapability
+	if capabilityForType(capabilities, capabilityName) != nil {
+		return true
+	}
+	if capabilityForType(capabilities, "omni") != nil {
+		return true
+	}
+	originalTypes := stringListFromAny(capabilities["originalTypes"])
+	return containsString(originalTypes, capabilityName) || containsString(originalTypes, "omni")
+}
+
+func imageURLFromContentPart(part map[string]any) string {
+	return urlFromNestedContentPart(part, "image_url", "url", "imageUrl")
+}
+
+func videoURLFromContentPart(part map[string]any) string {
+	return urlFromNestedContentPart(part, "video_url", "url", "videoUrl")
+}
+
+func audioURLFromContentPart(part map[string]any) string {
+	if stringFromAny(part["type"]) == "input_audio" {
+		if audio, ok := part["input_audio"].(map[string]any); ok {
+			if url := firstNonEmptyString(stringFromAny(audio["data"]), stringFromAny(audio["url"])); url != "" {
+				return url
+			}
+		}
+	}
+	return urlFromNestedContentPart(part, "audio_url", "url", "audioUrl")
+}
+
+func urlFromNestedContentPart(part map[string]any, keys ...string) string {
+	for _, key := range keys {
+		value := part[key]
+		if url := stringFromAny(value); url != "" {
+			return url
+		}
+		if nested, ok := value.(map[string]any); ok {
+			if url := stringFromAny(nested["url"]); url != "" {
+				return url
+			}
+		}
+	}
+	return ""
+}
+
 type contentFilterProcessor struct{}
 
 func (contentFilterProcessor) Name() string { return "ContentFilterProcessor" }
@@ -1239,6 +1429,9 @@ func capabilityValue(capabilities map[string]any, modelType string, key string)
 	if capability == nil {
 		return nil
 	}
+	if strings.TrimSpace(key) == "" {
+		return cloneMap(capability)
+	}
 	return cloneAny(capability[key])
 }
 
diff --git a/apps/api/internal/runner/param_processor_test.go b/apps/api/internal/runner/param_processor_test.go
index 34ab9f8..f4130ae 100644
--- a/apps/api/internal/runner/param_processor_test.go
+++ b/apps/api/internal/runner/param_processor_test.go
@@ -123,6 +123,163 @@ func TestParamProcessorOmniCapabilityLogUsesActualCapabilityKey(t *testing.T) {
 	t.Fatalf("expected log to reference capabilities.omni.input_audio, got %+v", result.Log.Changes)
 }
 
+func TestParamProcessorChatConvertsUnsupportedMediaMessageContentToText(t *testing.T) {
+	body := map[string]any{
+		"model": "text-only",
+		"messages": []any{
+			map[string]any{
+				"role": "user",
+				"content": []any{
+					map[string]any{"type": "text", "text": "describe these"},
+					map[string]any{"type": "image_url", "image_url": map[string]any{"url": "https://example.com/image.png"}},
+					map[string]any{"type": "video_url", "video_url": map[string]any{"url": "https://example.com/video.mp4"}},
+					map[string]any{"type": "audio_url", "audio_url": map[string]any{"url": "https://example.com/audio.mp3"}},
+					map[string]any{"type": "input_audio", "input_audio": map[string]any{"data": "https://example.com/input.wav"}},
+				},
+			},
+		},
+	}
+	candidate := store.RuntimeModelCandidate{
+		ModelType: "text_generate",
+		Capabilities: map[string]any{
+			"text_generate": map[string]any{},
+			"originalTypes": []any{"text_generate"},
+		},
+	}
+
+	result := preprocessRequestWithLog("chat.completions", body, candidate)
+	messages, _ := result.Body["messages"].([]any)
+	if len(messages) != 1 {
+		t.Fatalf("expected one message, got %+v", result.Body["messages"])
+	}
+	message, _ := messages[0].(map[string]any)
+	content, _ := message["content"].([]any)
+	if len(content) != 5 {
+		t.Fatalf("expected five content parts, got %+v", message["content"])
+	}
+	expectedText := []string{
+		"describe these",
+		"Image link: https://example.com/image.png",
+		"video URL: https://example.com/video.mp4",
+		"audio URL: https://example.com/audio.mp3",
+		"audio URL: https://example.com/input.wav",
+	}
+	for index, expected := range expectedText {
+		part, _ := content[index].(map[string]any)
+		if stringFromAny(part["text"]) != expected {
+			t.Fatalf("content[%d] text = %q, want %q; all=%+v", index, stringFromAny(part["text"]), expected, content)
+		}
+	}
+	if len(result.Log.Changes) != 4 {
+		t.Fatalf("expected four media conversion changes, got %+v", result.Log.Changes)
+	}
+	expectedCapabilityPaths := map[string]bool{
+		"capabilities.image_analysis":      false,
+		"capabilities.video_understanding": false,
+		"capabilities.audio_understanding": false,
+	}
+	for _, change := range result.Log.Changes {
+		if _, ok := expectedCapabilityPaths[change.CapabilityPath]; ok {
+			expectedCapabilityPaths[change.CapabilityPath] = true
+		}
+	}
+	for path, found := range expectedCapabilityPaths {
+		if !found {
+			t.Fatalf("expected conversion log for %s, got %+v", path, result.Log.Changes)
+		}
+	}
+}
+
+func TestParamProcessorChatKeepsOmniMessageContent(t *testing.T) {
+	body := map[string]any{
+		"model": "omni",
+		"messages": []any{
+			map[string]any{
+				"role": "user",
+				"content": []any{
+					map[string]any{"type": "image_url", "image_url": map[string]any{"url": "https://example.com/image.png"}},
+					map[string]any{"type": "video_url", "video_url": map[string]any{"url": "https://example.com/video.mp4"}},
+					map[string]any{"type": "audio_url", "audio_url": map[string]any{"url": "https://example.com/audio.mp3"}},
+				},
+			},
+		},
+	}
+	candidate := store.RuntimeModelCandidate{
+		ModelType: "text_generate",
+		Capabilities: map[string]any{
+			"text_generate": map[string]any{},
+			"omni":          map[string]any{},
+			"originalTypes": []any{"text_generate", "omni"},
+		},
+	}
+
+	result := preprocessRequestWithLog("chat.completions", body, candidate)
+	if result.Log.Changed {
+		t.Fatalf("omni model should keep message media content unchanged, got %+v", result.Log.Changes)
+	}
+	messages, _ := result.Body["messages"].([]any)
+	message, _ := messages[0].(map[string]any)
+	content, _ := message["content"].([]any)
+	for _, item := range content {
+		part, _ := item.(map[string]any)
+		if stringFromAny(part["type"]) == "text" {
+			t.Fatalf("media content should not be converted for omni model: %+v", content)
+		}
+	}
+}
+
+func TestParamProcessorChatConvertsOnlyUnsupportedModalities(t *testing.T) {
+	body := map[string]any{
+		"model": "vision-only",
+		"messages": []any{
+			map[string]any{
+				"role": "user",
+				"content": []any{
+					map[string]any{"type": "image_url", "image_url": map[string]any{"url": "https://example.com/image.png"}},
+					map[string]any{"type": "video_url", "video_url": map[string]any{"url": "https://example.com/video.mp4"}},
+				},
+			},
+		},
+	}
+	candidate := store.RuntimeModelCandidate{
+		ModelType: "text_generate",
+		Capabilities: map[string]any{
+			"text_generate":  map[string]any{},
+			"image_analysis": map[string]any{},
+			"originalTypes":  []any{"text_generate", "image_analysis"},
+		},
+	}
+
+	result := preprocessRequestWithLog("chat.completions", body, candidate)
+	messages, _ := result.Body["messages"].([]any)
+	message, _ := messages[0].(map[string]any)
+	content, _ := message["content"].([]any)
+	first, _ := content[0].(map[string]any)
+	second, _ := content[1].(map[string]any)
+	if stringFromAny(first["type"]) != "image_url" {
+		t.Fatalf("image content should be kept when image_analysis is supported: %+v", content)
+	}
+	if stringFromAny(second["text"]) != "video URL: https://example.com/video.mp4" {
+		t.Fatalf("video content should be converted, got %+v", second)
+	}
+	if len(result.Log.Changes) != 1 || result.Log.Changes[0].CapabilityPath != "capabilities.video_understanding" {
+		t.Fatalf("expected only video conversion to be logged, got %+v", result.Log.Changes)
+	}
+}
+
+func TestSkipTaskParameterPreprocessingLogForTextModelTypes(t *testing.T) {
+	for _, modelType := range []string{"text_generate", "chat", "responses", "text"} {
+		if !skipTaskParameterPreprocessingLog(modelType) {
+			t.Fatalf("%s should skip task parameter preprocessing log", modelType)
+		}
+	}
+	for _, modelType := range []string{"image_generate", "image_edit", "video_generate", "omni_video"} {
+		if skipTaskParameterPreprocessingLog(modelType) {
+			t.Fatalf("%s should keep task parameter preprocessing log", modelType)
+		}
+	}
+}
+
 func TestParamProcessorVideoCapabilitiesNormalizeAndFilter(t *testing.T) {
 	body := map[string]any{
 		"model":        "Seedance",
diff --git a/apps/api/internal/runner/service.go b/apps/api/internal/runner/service.go
index 116da1a..e5cc2e8 100644
--- a/apps/api/internal/runner/service.go
+++ b/apps/api/internal/runner/service.go
@@ -531,6 +531,9 @@ func (s *Service) runCandidate(ctx context.Context, task store.GatewayTask, user
 }
 
 func (s *Service) recordTaskParameterPreprocessing(ctx context.Context, taskID string, attemptID string, attemptNo int, candidate store.RuntimeModelCandidate, log parameterPreprocessingLog) error {
+	if skipTaskParameterPreprocessingLog(log.ModelType) {
+		return nil
+	}
 	_, err := s.store.CreateTaskParamPreprocessingLog(ctx, store.CreateTaskParamPreprocessingLogInput{
 		TaskID:          taskID,
 		AttemptID:       attemptID,
@@ -549,6 +552,15 @@ func (s *Service) recordTaskParameterPreprocessing(ctx context.Context, taskID s
 	return err
 }
 
+func skipTaskParameterPreprocessingLog(modelType string) bool {
+	switch strings.TrimSpace(modelType) {
+	case "text_generate", "chat", "responses", "text":
+		return true
+	default:
+		return false
+	}
+}
+
 func (s *Service) clientFor(candidate store.RuntimeModelCandidate, simulated bool) clients.Client {
 	if simulated {
 		return s.clients["simulation"]