feat(pico): add support for tool_calls in chat messages

web/backend/api/session.go

@@ -2,7 +2,6 @@ package api
 
 import (
 	"bufio"
-	"bytes"
 	"encoding/json"
 	"errors"
 	"net/http"
@@ -53,6 +52,7 @@ type sessionChatMessage struct {
 	Kind        string                  `json:"kind,omitempty"`
 	Media       []string                `json:"media,omitempty"`
 	Attachments []sessionChatAttachment `json:"attachments,omitempty"`
+	ToolCalls   []utils.VisibleToolCall `json:"tool_calls,omitempty"`
 }
 
 type sessionChatAttachment struct {
@@ -456,7 +456,10 @@ func truncateRunes(s string, maxLen int) string {
 }
 
 func sessionChatMessageVisible(msg sessionChatMessage) bool {
-	return strings.TrimSpace(msg.Content) != "" || len(msg.Media) > 0 || len(msg.Attachments) > 0
+	return strings.TrimSpace(msg.Content) != "" ||
+		len(msg.Media) > 0 ||
+		len(msg.Attachments) > 0 ||
+		len(msg.ToolCalls) > 0
 }
 
 func sessionChatMessagePreview(msg sessionChatMessage) string {
@@ -475,6 +478,9 @@ func sessionChatMessagePreview(msg sessionChatMessage) string {
 		}
 		return "[attachment]"
 	}
+	if len(msg.ToolCalls) > 0 {
+		return "[tool call]"
+	}
 	return ""
 }
 
@@ -521,25 +527,11 @@ func sessionTranscriptMessages(
 				}
 			}
 
-			toolSummaryMessages := visibleAssistantToolSummaryMessages(msg.ToolCalls, toolFeedbackMaxArgsLength)
-			if len(toolSummaryMessages) > 0 {
-				transcript = append(transcript, toolSummaryMessages...)
-			}
-
+			toolCallsMsg, hasToolCallsMsg := assistantToolCallsMessage(
+				msg.ToolCalls,
+				toolFeedbackMaxArgsLength,
+			)
 			visibleToolMessages := visibleAssistantToolMessages(msg.ToolCalls)
-			if len(visibleToolMessages) > 0 {
-				transcript = append(transcript, visibleToolMessages...)
-			}
-
-			// When assistant content exactly matches the rendered tool summary or
-			// tool-delivered message, skip it to avoid duplicates. Distinct content
-			// must remain visible in restored session history.
-			if len(msg.ToolCalls) > 0 &&
-				len(msg.Media) == 0 &&
-				len(attachments) == 0 &&
-				assistantToolCallContentDuplicated(msg.Content, toolSummaryMessages, visibleToolMessages) {
-				continue
-			}
 
 			// Pico web chat can persist both visible `message` tool output and a
 			// later plain assistant reply in the same turn. Hide only the fixed
@@ -547,6 +539,12 @@ func sessionTranscriptMessages(
 			content := msg.Content
 			if assistantMessageInternalOnly(msg) {
 				if len(attachments) == 0 {
+					if hasToolCallsMsg {
+						transcript = append(transcript, toolCallsMsg)
+					}
+					if len(visibleToolMessages) > 0 {
+						transcript = append(transcript, visibleToolMessages...)
+					}
 					continue
 				}
 				content = ""
@@ -559,10 +557,22 @@ func sessionTranscriptMessages(
 				Attachments: attachments,
 			}
 			if !sessionChatMessageVisible(chatMsg) {
+				if hasToolCallsMsg {
+					transcript = append(transcript, toolCallsMsg)
+				}
+				if len(visibleToolMessages) > 0 {
+					transcript = append(transcript, visibleToolMessages...)
+				}
 				continue
 			}
 
 			transcript = append(transcript, chatMsg)
+			if hasToolCallsMsg {
+				transcript = append(transcript, toolCallsMsg)
+			}
+			if len(visibleToolMessages) > 0 {
+				transcript = append(transcript, visibleToolMessages...)
+			}
 		}
 	}
 
@@ -580,51 +590,6 @@ func filterSessionChatMessages(messages []sessionChatMessage) []sessionChatMessa
 	return filtered
 }
 
-func assistantToolCallContentDuplicated(
-	content string,
-	toolSummaryMessages []sessionChatMessage,
-	visibleToolMessages []sessionChatMessage,
-) bool {
-	content = strings.TrimSpace(content)
-	if content == "" {
-		return false
-	}
-
-	for _, msg := range toolSummaryMessages {
-		if toolSummaryContainsContent(msg.Content, content) {
-			return true
-		}
-	}
-	for _, msg := range visibleToolMessages {
-		if strings.TrimSpace(msg.Content) == content {
-			return true
-		}
-	}
-	return false
-}
-
-func toolSummaryContainsContent(summary, content string) bool {
-	summary = strings.TrimSpace(summary)
-	content = strings.TrimSpace(content)
-	if summary == "" || content == "" {
-		return false
-	}
-	if summary == content {
-		return true
-	}
-
-	_, body, hasBody := strings.Cut(summary, "\n")
-	if !hasBody {
-		return false
-	}
-	body = strings.TrimSpace(body)
-	if body == content {
-		return true
-	}
-	firstSection, _, _ := strings.Cut(body, "\n```")
-	return strings.TrimSpace(firstSection) == content
-}
-
 func sessionAttachments(msg providers.Message) []sessionChatAttachment {
 	if len(msg.Attachments) == 0 {
 		return nil
@@ -720,80 +685,34 @@ func assistantThoughtMessage(msg providers.Message) (sessionChatMessage, bool) {
 	}, true
 }
 
-func visibleAssistantToolSummaryMessages(
+func assistantToolCallsMessage(
 	toolCalls []providers.ToolCall,
 	toolFeedbackMaxArgsLength int,
-) []sessionChatMessage {
+) (sessionChatMessage, bool) {
 	if len(toolCalls) == 0 {
-		return nil
+		return sessionChatMessage{}, false
 	}
 	if toolFeedbackMaxArgsLength <= 0 {
 		toolFeedbackMaxArgsLength = defaultToolFeedbackMaxArgsLength()
 	}
 
-	messages := make([]sessionChatMessage, 0, len(toolCalls))
-	for _, tc := range toolCalls {
-		name, argsJSON := toolCallNameAndArguments(tc)
-		if strings.TrimSpace(name) == "" {
-			continue
-		}
-		if name == "web_search" || name == "web_fetch" {
-			continue
-		}
-		if name == "message" {
-			if _, ok := parseMessageToolContent(argsJSON); ok {
-				continue
-			}
-		}
-
-		messages = append(messages, sessionChatMessage{
-			Role: "assistant",
-			Content: utils.FormatToolFeedbackMessage(
-				name,
-				visibleAssistantToolFeedbackExplanation(tc, toolFeedbackMaxArgsLength),
-				visibleAssistantToolArgsPreview(tc, toolFeedbackMaxArgsLength),
-			),
-		})
+	visibleToolCalls := utils.BuildVisibleToolCalls(toolCalls, toolFeedbackMaxArgsLength)
+	if len(visibleToolCalls) == 0 {
+		return sessionChatMessage{}, false
 	}
 
-	return messages
-}
-
-func visibleAssistantToolFeedbackExplanation(
-	tc providers.ToolCall,
-	toolFeedbackMaxArgsLength int,
-) string {
-	if tc.ExtraContent != nil {
-		if explanation := strings.TrimSpace(tc.ExtraContent.ToolFeedbackExplanation); explanation != "" {
-			return utils.Truncate(explanation, toolFeedbackMaxArgsLength)
-		}
-	}
-	return ""
+	return sessionChatMessage{
+		Role:      "assistant",
+		Kind:      "tool_calls",
+		ToolCalls: visibleToolCalls,
+	}, true
 }
 
 func visibleAssistantToolArgsPreview(
 	tc providers.ToolCall,
 	toolFeedbackMaxArgsLength int,
 ) string {
-	argsJSON := ""
-	if tc.Function != nil {
-		argsJSON = tc.Function.Arguments
-	}
-	if strings.TrimSpace(argsJSON) == "" && len(tc.Arguments) > 0 {
-		if encodedArgs, err := json.MarshalIndent(tc.Arguments, "", "  "); err == nil {
-			argsJSON = string(encodedArgs)
-		}
-	}
-	argsJSON = strings.TrimSpace(argsJSON)
-	if argsJSON == "" {
-		return ""
-	}
-	var pretty bytes.Buffer
-	if err := json.Indent(&pretty, []byte(argsJSON), "", "  "); err == nil {
-		argsJSON = pretty.String()
-	}
-
-	return utils.Truncate(argsJSON, toolFeedbackMaxArgsLength)
+	return utils.VisibleToolCallArgumentsPreview(tc, toolFeedbackMaxArgsLength)
 }
 
 func visibleAssistantToolMessages(toolCalls []providers.ToolCall) []sessionChatMessage {
@@ -803,7 +722,7 @@ func visibleAssistantToolMessages(toolCalls []providers.ToolCall) []sessionChatM
 
 	messages := make([]sessionChatMessage, 0, len(toolCalls))
 	for _, tc := range toolCalls {
-		name, argsJSON := toolCallNameAndArguments(tc)
+		name, argsJSON := utils.VisibleToolCallNameAndArguments(tc)
 		if name != "message" {
 			continue
 		}
@@ -820,23 +739,6 @@ func visibleAssistantToolMessages(toolCalls []providers.ToolCall) []sessionChatM
 	return messages
 }
 
-func toolCallNameAndArguments(tc providers.ToolCall) (string, string) {
-	name := tc.Name
-	argsJSON := ""
-	if tc.Function != nil {
-		if name == "" {
-			name = tc.Function.Name
-		}
-		argsJSON = tc.Function.Arguments
-	}
-	if strings.TrimSpace(argsJSON) == "" && len(tc.Arguments) > 0 {
-		if encodedArgs, err := json.Marshal(tc.Arguments); err == nil {
-			argsJSON = string(encodedArgs)
-		}
-	}
-	return name, argsJSON
-}
-
 func parseMessageToolContent(argsJSON string) (string, bool) {
 	var args struct {
 		Content string `json:"content"`

web/backend/api/session_test.go

@@ -32,6 +32,25 @@ func sessionsTestDir(t *testing.T, configPath string) string {
 	return dir
 }
 
+func assertVisibleToolCallMessage(
+	t *testing.T,
+	msg sessionChatMessage,
+	toolName string,
+) utils.VisibleToolCall {
+	t.Helper()
+
+	if msg.Role != "assistant" || msg.Kind != "tool_calls" {
+		t.Fatalf("message = %#v, want assistant/tool_calls", msg)
+	}
+	if len(msg.ToolCalls) != 1 {
+		t.Fatalf("len(message.ToolCalls) = %d, want 1", len(msg.ToolCalls))
+	}
+	if got := msg.ToolCalls[0].Function; got == nil || got.Name != toolName {
+		t.Fatalf("tool call = %#v, want function %q", msg.ToolCalls[0], toolName)
+	}
+	return msg.ToolCalls[0]
+}
+
 func TestHandleListSessions_JSONLStorage(t *testing.T) {
 	configPath, cleanup := setupOAuthTestEnv(t)
 	defer cleanup()
@@ -516,11 +535,7 @@ func TestHandleGetSession_SkipsTransientThoughtMessages(t *testing.T) {
 	}
 
 	var resp struct {
-		Messages []struct {
-			Role    string `json:"role"`
-			Content string `json:"content"`
-			Kind    string `json:"kind"`
-		} `json:"messages"`
+		Messages []sessionChatMessage `json:"messages"`
 	}
 	if err := json.Unmarshal(rec.Body.Bytes(), &resp); err != nil {
 		t.Fatalf("Unmarshal() error = %v", err)
@@ -569,11 +584,7 @@ func TestHandleGetSession_ReconstructsThoughtFromAssistantReasoningContent(t *te
 	}
 
 	var resp struct {
-		Messages []struct {
-			Role    string `json:"role"`
-			Content string `json:"content"`
-			Kind    string `json:"kind"`
-		} `json:"messages"`
+		Messages []sessionChatMessage `json:"messages"`
 	}
 	if err := json.Unmarshal(rec.Body.Bytes(), &resp); err != nil {
 		t.Fatalf("Unmarshal() error = %v", err)
@@ -667,11 +678,7 @@ func TestHandleGetSession_ReconstructsRefreshMatrixForThoughtAndToolSummary(t *t
 	}
 
 	var resp struct {
-		Messages []struct {
-			Role    string `json:"role"`
-			Content string `json:"content"`
-			Kind    string `json:"kind"`
-		} `json:"messages"`
+		Messages []sessionChatMessage `json:"messages"`
 	}
 	if err := json.Unmarshal(rec.Body.Bytes(), &resp); err != nil {
 		t.Fatalf("Unmarshal() error = %v", err)
@@ -694,20 +701,14 @@ func TestHandleGetSession_ReconstructsRefreshMatrixForThoughtAndToolSummary(t *t
 	assertMessage(2, "assistant", "", "plain visible")
 	assertMessage(3, "user", "", "turn2")
 	assertMessage(4, "assistant", "thought", "tool thought")
-	if !strings.Contains(resp.Messages[5].Content, "`read_file`") {
-		t.Fatalf("messages[5] = %#v, want read_file tool summary", resp.Messages[5])
-	}
+	assertVisibleToolCallMessage(t, resp.Messages[5], "read_file")
 	assertMessage(6, "user", "", "turn3")
-	if !strings.Contains(resp.Messages[7].Content, "`list_dir`") {
-		t.Fatalf("messages[7] = %#v, want list_dir tool summary", resp.Messages[7])
-	}
-	assertMessage(8, "assistant", "", "tool visible only")
+	assertMessage(7, "assistant", "", "tool visible only")
+	assertVisibleToolCallMessage(t, resp.Messages[8], "list_dir")
 	assertMessage(9, "user", "", "turn4")
 	assertMessage(10, "assistant", "thought", "tool mixed thought")
-	if !strings.Contains(resp.Messages[11].Content, "`exec`") {
-		t.Fatalf("messages[11] = %#v, want exec tool summary", resp.Messages[11])
-	}
-	assertMessage(12, "assistant", "", "tool visible and thought")
+	assertMessage(11, "assistant", "", "tool visible and thought")
+	assertVisibleToolCallMessage(t, resp.Messages[12], "exec")
 }
 
 func TestHandleGetSession_ReconstructsVisibleMessageToolOutputWithoutDuplicateSummary(t *testing.T) {
@@ -758,27 +759,20 @@ func TestHandleGetSession_ReconstructsVisibleMessageToolOutputWithoutDuplicateSu
 	}
 
 	var resp struct {
-		Messages []struct {
-			Role    string `json:"role"`
-			Content string `json:"content"`
-		} `json:"messages"`
+		Messages []sessionChatMessage `json:"messages"`
 	}
 	if err := json.Unmarshal(rec.Body.Bytes(), &resp); err != nil {
 		t.Fatalf("Unmarshal() error = %v", err)
 	}
-	if len(resp.Messages) != 2 {
-		t.Fatalf("len(resp.Messages) = %d, want 2", len(resp.Messages))
+	if len(resp.Messages) != 3 {
+		t.Fatalf("len(resp.Messages) = %d, want 3", len(resp.Messages))
 	}
 	if resp.Messages[0].Role != "user" || resp.Messages[0].Content != "test" {
 		t.Fatalf("first message = %#v, want user/test", resp.Messages[0])
 	}
-	if resp.Messages[1].Role != "assistant" || resp.Messages[1].Content != "visible tool output" {
-		t.Fatalf("assistant message = %#v, want visible tool output", resp.Messages[1])
-	}
-	for _, msg := range resp.Messages {
-		if msg.Role == "tool" || strings.Contains(msg.Content, "`message`") {
-			t.Fatalf("unexpected raw tool or duplicate message-tool summary: %#v", msg)
-		}
+	assertVisibleToolCallMessage(t, resp.Messages[1], "message")
+	if resp.Messages[2].Role != "assistant" || resp.Messages[2].Content != "visible tool output" {
+		t.Fatalf("assistant message = %#v, want visible tool output", resp.Messages[2])
 	}
 }
 
@@ -829,25 +823,23 @@ func TestHandleGetSession_PreservesFinalAssistantReplyAfterMessageToolOutput(t *
 	}
 
 	var resp struct {
-		Messages []struct {
-			Role    string `json:"role"`
-			Content string `json:"content"`
-		} `json:"messages"`
+		Messages []sessionChatMessage `json:"messages"`
 	}
 	if err := json.Unmarshal(rec.Body.Bytes(), &resp); err != nil {
 		t.Fatalf("Unmarshal() error = %v", err)
 	}
-	if len(resp.Messages) != 3 {
-		t.Fatalf("len(resp.Messages) = %d, want 3", len(resp.Messages))
+	if len(resp.Messages) != 4 {
+		t.Fatalf("len(resp.Messages) = %d, want 4", len(resp.Messages))
 	}
 	if resp.Messages[0].Role != "user" || resp.Messages[0].Content != "test" {
 		t.Fatalf("first message = %#v, want user/test", resp.Messages[0])
 	}
-	if resp.Messages[1].Role != "assistant" || resp.Messages[1].Content != "visible tool output" {
-		t.Fatalf("interim assistant message = %#v, want visible tool output", resp.Messages[1])
+	assertVisibleToolCallMessage(t, resp.Messages[1], "message")
+	if resp.Messages[2].Role != "assistant" || resp.Messages[2].Content != "visible tool output" {
+		t.Fatalf("interim assistant message = %#v, want visible tool output", resp.Messages[2])
 	}
-	if resp.Messages[2].Role != "assistant" || resp.Messages[2].Content != "final assistant reply" {
-		t.Fatalf("final assistant message = %#v, want final assistant reply", resp.Messages[2])
+	if resp.Messages[3].Role != "assistant" || resp.Messages[3].Content != "final assistant reply" {
+		t.Fatalf("final assistant message = %#v, want final assistant reply", resp.Messages[3])
 	}
 }
 
@@ -904,8 +896,8 @@ func TestHandleListSessions_MessageCountUsesVisibleTranscript(t *testing.T) {
 	if len(items) != 1 {
 		t.Fatalf("len(items) = %d, want 1", len(items))
 	}
-	if items[0].MessageCount != 2 {
-		t.Fatalf("items[0].MessageCount = %d, want 2", items[0].MessageCount)
+	if items[0].MessageCount != 3 {
+		t.Fatalf("items[0].MessageCount = %d, want 3", items[0].MessageCount)
 	}
 }
 
@@ -959,25 +951,24 @@ func TestHandleGetSession_DoesNotDuplicateAssistantToolCallContent(t *testing.T)
 	}
 
 	var resp struct {
-		Messages []struct {
-			Role    string `json:"role"`
-			Content string `json:"content"`
-		} `json:"messages"`
+		Messages []sessionChatMessage `json:"messages"`
 	}
 	if err := json.Unmarshal(rec.Body.Bytes(), &resp); err != nil {
 		t.Fatalf("Unmarshal() error = %v", err)
 	}
-	if len(resp.Messages) != 2 {
-		t.Fatalf("len(resp.Messages) = %d, want 2", len(resp.Messages))
+	if len(resp.Messages) != 3 {
+		t.Fatalf("len(resp.Messages) = %d, want 3", len(resp.Messages))
 	}
 	if resp.Messages[0].Role != "user" || resp.Messages[0].Content != "check file" {
 		t.Fatalf("first message = %#v, want user/check file", resp.Messages[0])
 	}
-	if !strings.Contains(resp.Messages[1].Content, "`read_file`") {
-		t.Fatalf("tool summary message = %#v, want read_file summary", resp.Messages[1])
+	if resp.Messages[1].Content != "Read the file before replying." {
+		t.Fatalf("assistant content = %#v, want preserved assistant content", resp.Messages[1])
 	}
-	if !strings.Contains(resp.Messages[1].Content, "Read the file before replying.") {
-		t.Fatalf("tool summary message = %#v, want tool explanation", resp.Messages[1])
+	toolCall := assertVisibleToolCallMessage(t, resp.Messages[2], "read_file")
+	if toolCall.ExtraContent == nil ||
+		toolCall.ExtraContent.ToolFeedbackExplanation != "Read the file before replying." {
+		t.Fatalf("tool call = %#v, want explanation", toolCall)
 	}
 }
 
@@ -1030,10 +1021,7 @@ func TestHandleGetSession_PreservesDistinctAssistantToolCallContent(t *testing.T
 	}
 
 	var resp struct {
-		Messages []struct {
-			Role    string `json:"role"`
-			Content string `json:"content"`
-		} `json:"messages"`
+		Messages []sessionChatMessage `json:"messages"`
 	}
 	if err := json.Unmarshal(rec.Body.Bytes(), &resp); err != nil {
 		t.Fatalf("Unmarshal() error = %v", err)
@@ -1041,13 +1029,11 @@ func TestHandleGetSession_PreservesDistinctAssistantToolCallContent(t *testing.T
 	if len(resp.Messages) != 3 {
 		t.Fatalf("len(resp.Messages) = %d, want 3", len(resp.Messages))
 	}
-	if !strings.Contains(resp.Messages[1].Content, "`read_file`") {
-		t.Fatalf("tool summary message = %#v, want read_file summary", resp.Messages[1])
-	}
-	if resp.Messages[2].Role != "assistant" ||
-		resp.Messages[2].Content != "I will summarize the findings after reading the file." {
-		t.Fatalf("assistant content = %#v, want preserved distinct content", resp.Messages[2])
+	if resp.Messages[1].Role != "assistant" ||
+		resp.Messages[1].Content != "I will summarize the findings after reading the file." {
+		t.Fatalf("assistant content = %#v, want preserved distinct content", resp.Messages[1])
 	}
+	assertVisibleToolCallMessage(t, resp.Messages[2], "read_file")
 }
 
 func TestHandleGetSession_PreservesMediaWhenAssistantToolCallContentDuplicatesSummary(t *testing.T) {
@@ -1100,11 +1086,7 @@ func TestHandleGetSession_PreservesMediaWhenAssistantToolCallContentDuplicatesSu
 	}
 
 	var resp struct {
-		Messages []struct {
-			Role    string   `json:"role"`
-			Content string   `json:"content"`
-			Media   []string `json:"media"`
-		} `json:"messages"`
+		Messages []sessionChatMessage `json:"messages"`
 	}
 	if err := json.Unmarshal(rec.Body.Bytes(), &resp); err != nil {
 		t.Fatalf("Unmarshal() error = %v", err)
@@ -1112,23 +1094,16 @@ func TestHandleGetSession_PreservesMediaWhenAssistantToolCallContentDuplicatesSu
 	if len(resp.Messages) != 3 {
 		t.Fatalf("len(resp.Messages) = %d, want 3", len(resp.Messages))
 	}
-	if !strings.Contains(resp.Messages[1].Content, "`view_image`") {
-		t.Fatalf("tool summary message = %#v, want view_image summary", resp.Messages[1])
+	if resp.Messages[1].Role != "assistant" {
+		t.Fatalf("assistant message role = %q, want assistant", resp.Messages[1].Role)
 	}
-	if resp.Messages[2].Role != "assistant" {
-		t.Fatalf("assistant message role = %q, want assistant", resp.Messages[2].Role)
+	if resp.Messages[1].Content != "Reviewing the generated screenshot." {
+		t.Fatalf("assistant content = %q, want preserved duplicated content with media", resp.Messages[1].Content)
 	}
-	if resp.Messages[2].Content != "Reviewing the generated screenshot." {
-		t.Fatalf("assistant content = %q, want preserved duplicated content with media", resp.Messages[2].Content)
-	}
-	if len(resp.Messages[2].Media) != 1 || resp.Messages[2].Media[0] != "data:image/png;base64,abc123" {
-		t.Fatalf("assistant media = %#v, want preserved media", resp.Messages[2].Media)
-	}
-	for _, msg := range resp.Messages {
-		if msg.Role == "tool" || strings.Contains(msg.Content, "raw read_file result") {
-			t.Fatalf("unexpected raw tool result in history: %#v", msg)
-		}
+	if len(resp.Messages[1].Media) != 1 || resp.Messages[1].Media[0] != "data:image/png;base64,abc123" {
+		t.Fatalf("assistant media = %#v, want preserved media", resp.Messages[1].Media)
 	}
+	assertVisibleToolCallMessage(t, resp.Messages[2], "view_image")
 }
 
 func TestHandleGetSession_PreservesAttachmentsWhenAssistantToolCallContentDuplicatesSummary(t *testing.T) {
@@ -1198,21 +1173,19 @@ func TestHandleGetSession_PreservesAttachmentsWhenAssistantToolCallContentDuplic
 	if len(resp.Messages) != 3 {
 		t.Fatalf("len(resp.Messages) = %d, want 3", len(resp.Messages))
 	}
-	if !strings.Contains(resp.Messages[1].Content, "`read_file`") {
-		t.Fatalf("tool summary message = %#v, want read_file summary", resp.Messages[1])
+	if resp.Messages[1].Role != "assistant" {
+		t.Fatalf("assistant message role = %q, want assistant", resp.Messages[1].Role)
 	}
-	if resp.Messages[2].Role != "assistant" {
-		t.Fatalf("assistant message role = %q, want assistant", resp.Messages[2].Role)
+	if resp.Messages[1].Content != "Reviewing the generated report." {
+		t.Fatalf("assistant content = %q, want preserved duplicated content", resp.Messages[1].Content)
 	}
-	if resp.Messages[2].Content != "Reviewing the generated report." {
-		t.Fatalf("assistant content = %q, want preserved duplicated content", resp.Messages[2].Content)
+	if len(resp.Messages[1].Attachments) != 1 {
+		t.Fatalf("len(assistant.Attachments) = %d, want 1", len(resp.Messages[1].Attachments))
 	}
-	if len(resp.Messages[2].Attachments) != 1 {
-		t.Fatalf("len(assistant.Attachments) = %d, want 1", len(resp.Messages[2].Attachments))
-	}
-	if resp.Messages[2].Attachments[0].URL != "https://example.com/report.txt" {
-		t.Fatalf("attachment url = %q, want report URL", resp.Messages[2].Attachments[0].URL)
+	if resp.Messages[1].Attachments[0].URL != "https://example.com/report.txt" {
+		t.Fatalf("attachment url = %q, want report URL", resp.Messages[1].Attachments[0].URL)
 	}
+	assertVisibleToolCallMessage(t, resp.Messages[2], "read_file")
 }
 
 func TestHandleGetSession_UsesConfiguredToolFeedbackMaxArgsLength(t *testing.T) {
@@ -1273,10 +1246,7 @@ func TestHandleGetSession_UsesConfiguredToolFeedbackMaxArgsLength(t *testing.T)
 	}
 
 	var resp struct {
-		Messages []struct {
-			Role    string `json:"role"`
-			Content string `json:"content"`
-		} `json:"messages"`
+		Messages []sessionChatMessage `json:"messages"`
 	}
 	err = json.Unmarshal(rec.Body.Bytes(), &resp)
 	if err != nil {
@@ -1287,17 +1257,15 @@ func TestHandleGetSession_UsesConfiguredToolFeedbackMaxArgsLength(t *testing.T)
 	}
 
 	wantPreview := utils.Truncate(explanation, 20)
-	if !strings.Contains(resp.Messages[1].Content, wantPreview) {
-		t.Fatalf("tool summary = %q, want preview %q", resp.Messages[1].Content, wantPreview)
-	}
 	wantArgsPreview := visibleAssistantToolArgsPreview(providers.ToolCall{
 		Function: &providers.FunctionCall{Arguments: argsJSON},
 	}, 20)
-	if !strings.Contains(resp.Messages[1].Content, wantArgsPreview) {
-		t.Fatalf("tool summary = %q, want args preview %q", resp.Messages[1].Content, wantArgsPreview)
+	toolCall := assertVisibleToolCallMessage(t, resp.Messages[1], "read_file")
+	if toolCall.ExtraContent == nil || toolCall.ExtraContent.ToolFeedbackExplanation != wantPreview {
+		t.Fatalf("tool call = %#v, want preview %q", toolCall, wantPreview)
 	}
-	if !strings.Contains(resp.Messages[1].Content, "`read_file`") {
-		t.Fatalf("tool summary = %q, want read_file summary", resp.Messages[1].Content)
+	if toolCall.Function == nil || toolCall.Function.Arguments != wantArgsPreview {
+		t.Fatalf("tool call = %#v, want args preview %q", toolCall, wantArgsPreview)
 	}
 }
 
@@ -1357,10 +1325,7 @@ func TestHandleGetSession_FallsBackToLegacyToolArgumentsWhenExplanationMissing(t
 	}
 
 	var resp struct {
-		Messages []struct {
-			Role    string `json:"role"`
-			Content string `json:"content"`
-		} `json:"messages"`
+		Messages []sessionChatMessage `json:"messages"`
 	}
 	if err := json.Unmarshal(rec.Body.Bytes(), &resp); err != nil {
 		t.Fatalf("Unmarshal() error = %v", err)
@@ -1372,11 +1337,9 @@ func TestHandleGetSession_FallsBackToLegacyToolArgumentsWhenExplanationMissing(t
 	wantPreview := visibleAssistantToolArgsPreview(providers.ToolCall{
 		Function: &providers.FunctionCall{Arguments: argsJSON},
 	}, 20)
-	if !strings.Contains(resp.Messages[1].Content, "`read_file`") {
-		t.Fatalf("tool summary = %q, want read_file summary", resp.Messages[1].Content)
-	}
-	if !strings.Contains(resp.Messages[1].Content, wantPreview) {
-		t.Fatalf("tool summary = %q, want legacy args preview %q", resp.Messages[1].Content, wantPreview)
+	toolCall := assertVisibleToolCallMessage(t, resp.Messages[1], "read_file")
+	if toolCall.Function == nil || toolCall.Function.Arguments != wantPreview {
+		t.Fatalf("tool call = %#v, want legacy args preview %q", toolCall, wantPreview)
 	}
 }