Fix crash when parsing MCP server tool results

internal/parser/parser.go

@@ -65,10 +65,10 @@ type UserMessage struct {
 
 // ToolResult represents a tool result in a user message
 type ToolResult struct {
-	Type      string `json:"type"`
-	ToolUseID string `json:"tool_use_id"`
-	Content   string `json:"content"`
-	IsError   bool   `json:"is_error"`
+	Type      string          `json:"type"`
+	ToolUseID string          `json:"tool_use_id"`
+	Content   json.RawMessage `json:"content"`
+	IsError   bool            `json:"is_error"`
 }
 
 // ToolInput represents the input field for various tools
@@ -184,7 +184,7 @@ func parseUserMessage(raw RawMessage, timestamp time.Time) []StreamItem {
 				AgentID:   raw.AgentID,
 				AgentName: agentName,
 				Timestamp: timestamp,
-				Content:   result.Content,
+				Content:   extractToolResultContent(result.Content),
 				ToolID:    result.ToolUseID,
 			})
 		}
@@ -193,6 +193,38 @@ func parseUserMessage(raw RawMessage, timestamp time.Time) []StreamItem {
 	return items
 }
 
+// extractToolResultContent handles both string and array-of-blocks content.
+// Built-in tools return a plain string; MCP tools return [{"type":"text","text":"..."}].
+func extractToolResultContent(raw json.RawMessage) string {
+	if len(raw) == 0 {
+		return ""
+	}
+
+	// Try as plain string first (built-in tools)
+	var s string
+	if err := json.Unmarshal(raw, &s); err == nil {
+		return s
+	}
+
+	// Try as array of content blocks (MCP tools)
+	var blocks []struct {
+		Type string `json:"type"`
+		Text string `json:"text"`
+	}
+	if err := json.Unmarshal(raw, &blocks); err == nil {
+		var parts []string
+		for _, b := range blocks {
+			if b.Text != "" {
+				parts = append(parts, b.Text)
+			}
+		}
+		return strings.Join(parts, "\n")
+	}
+
+	// Fallback: return raw JSON
+	return string(raw)
+}
+
 func formatToolInput(toolName string, inputRaw json.RawMessage) string {
 	var input ToolInput
 	if err := json.Unmarshal(inputRaw, &input); err != nil {

internal/parser/parser_test.go

@@ -178,6 +178,43 @@ func TestParseLine_UserToolResult(t *testing.T) {
 	}
 }
 
+func TestParseLine_MCPToolResult(t *testing.T) {
+	// MCP tools return content as an array of content blocks, not a plain string
+	line := `{"type":"user","timestamp":"2025-01-01T12:00:00Z","message":{"role":"user","content":[{"type":"tool_result","tool_use_id":"toolu_mcp1","content":[{"type":"text","text":"MCP result here"}]}]}}`
+	items, err := ParseLine(line)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if len(items) != 1 {
+		t.Fatalf("expected 1 item, got %d", len(items))
+	}
+	item := items[0]
+	if item.Type != TypeToolOutput {
+		t.Errorf("type = %q, want %q", item.Type, TypeToolOutput)
+	}
+	if item.ToolID != "toolu_mcp1" {
+		t.Errorf("toolID = %q, want %q", item.ToolID, "toolu_mcp1")
+	}
+	if item.Content != "MCP result here" {
+		t.Errorf("content = %q, want %q", item.Content, "MCP result here")
+	}
+}
+
+func TestParseLine_MCPToolResultMultiBlock(t *testing.T) {
+	// MCP tools can return multiple content blocks
+	line := `{"type":"user","timestamp":"2025-01-01T12:00:00Z","message":{"role":"user","content":[{"type":"tool_result","tool_use_id":"toolu_mcp2","content":[{"type":"text","text":"block one"},{"type":"text","text":"block two"}]}]}}`
+	items, err := ParseLine(line)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if len(items) != 1 {
+		t.Fatalf("expected 1 item, got %d", len(items))
+	}
+	if items[0].Content != "block one\nblock two" {
+		t.Errorf("content = %q, want %q", items[0].Content, "block one\nblock two")
+	}
+}
+
 func TestParseLine_SubagentMessage(t *testing.T) {
 	line := `{"type":"assistant","agentId":"abc1234567890","timestamp":"2025-01-01T12:00:00Z","message":{"role":"assistant","content":[{"type":"thinking","thinking":"subagent thinking"}]}}`
 	items, err := ParseLine(line)