perf: replace []string+Join with strings.Builder in hot paths

Covers web search providers (Brave/Tavily/DuckDuckGo/extractText),
skills loader, logger formatFields, system prompt builder, and
Slack message handler. Eliminates intermediate slice allocations.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

pkg/agent/context.go

@@ -218,14 +218,16 @@ func (cb *ContextBuilder) BuildMessages(
 ) []providers.Message {
 	messages := []providers.Message{}
 
-	systemPrompt := cb.BuildSystemPrompt()
+	var sysBuilder strings.Builder
+	sysBuilder.WriteString(cb.BuildSystemPrompt())
 
 	// Add Current Session info if provided
 	if channel != "" && chatID != "" {
-		systemPrompt += fmt.Sprintf("\n\n## Current Session\nChannel: %s\nChat ID: %s", channel, chatID)
+		fmt.Fprintf(&sysBuilder, "\n\n## Current Session\nChannel: %s\nChat ID: %s", channel, chatID)
 	}
 
 	// Log system prompt summary for debugging (debug mode only)
+	systemPrompt := sysBuilder.String()
 	logger.DebugCF("agent", "System prompt built",
 		map[string]any{
 			"total_chars":   len(systemPrompt),
@@ -244,7 +246,9 @@ func (cb *ContextBuilder) BuildMessages(
 		})
 
 	if summary != "" {
-		systemPrompt += "\n\n## Summary of Previous Conversation\n\n" + summary
+		sysBuilder.WriteString("\n\n## Summary of Previous Conversation\n\n")
+		sysBuilder.WriteString(summary)
+		systemPrompt = sysBuilder.String()
 	}
 
 	history = sanitizeHistoryForProvider(history)

pkg/channels/slack.go

@@ -228,8 +228,8 @@ func (c *SlackChannel) handleMessageEvent(ev *slackevents.MessageEvent) {
 		Timestamp: messageTS,
 	})
 
-	content := ev.Text
+	var contentBuf strings.Builder
-	content = c.stripBotMention(content)
+	contentBuf.WriteString(c.stripBotMention(ev.Text))
 
 	var mediaPaths []string
 	localFiles := []string{} // 跟踪需要清理的本地文件
@@ -262,16 +262,17 @@ func (c *SlackChannel) handleMessageEvent(ev *slackevents.MessageEvent) {
 
 				if err != nil {
 					logger.ErrorCF("slack", "Voice transcription failed", map[string]any{"error": err.Error()})
-					content += fmt.Sprintf("\n[audio: %s (transcription failed)]", file.Name)
+					fmt.Fprintf(&contentBuf, "\n[audio: %s (transcription failed)]", file.Name)
 				} else {
-					content += fmt.Sprintf("\n[voice transcription: %s]", result.Text)
+					fmt.Fprintf(&contentBuf, "\n[voice transcription: %s]", result.Text)
 				}
 			} else {
-				content += fmt.Sprintf("\n[file: %s]", file.Name)
+				fmt.Fprintf(&contentBuf, "\n[file: %s]", file.Name)
 			}
 		}
 	}
 
+	content := contentBuf.String()
 	if strings.TrimSpace(content) == "" {
 		return
 	}

pkg/channels/telegram.go

@@ -7,6 +7,7 @@ import (
 	"net/url"
 	"os"
 	"regexp"
+	"strconv"
 	"strings"
 	"sync"
 	"time"
@@ -797,7 +798,7 @@ func extractCodeBlocks(text string) codeBlockMatch {
 
 	i := 0
 	text = re.ReplaceAllStringFunc(text, func(m string) string {
-		placeholder := fmt.Sprintf("\x00CB%d\x00", i)
+		placeholder := "\x00CB" + strconv.Itoa(i) + "\x00"
 		i++
 		return placeholder
 	})
@@ -821,7 +822,7 @@ func extractInlineCodes(text string) inlineCodeMatch {
 
 	i := 0
 	text = re.ReplaceAllStringFunc(text, func(m string) string {
-		placeholder := fmt.Sprintf("\x00IC%d\x00", i)
+		placeholder := "\x00IC" + strconv.Itoa(i) + "\x00"
 		i++
 		return placeholder
 	})

pkg/logger/logger.go

@@ -239,11 +239,18 @@ func formatComponent(component string) string {
 }
 
 func formatFields(fields map[string]any) string {
-	var parts []string
+	var sb strings.Builder
+	sb.WriteByte('{')
+	first := true
 	for k, v := range fields {
-		parts = append(parts, fmt.Sprintf("%s=%v", k, v))
+		if !first {
+			sb.WriteString(", ")
+		}
+		fmt.Fprintf(&sb, "%s=%v", k, v)
+		first = false
 	}
-	return fmt.Sprintf("{%s}", strings.Join(parts, ", "))
+	sb.WriteByte('}')
+	return sb.String()
 }
 
 func Debug(message string) {

pkg/skills/loader.go

@@ -214,15 +214,20 @@ func (sl *SkillsLoader) LoadSkillsForContext(skillNames []string) string {
 		return ""
 	}
 
-	var parts []string
+	var sb strings.Builder
+	first := true
 	for _, name := range skillNames {
 		content, ok := sl.LoadSkill(name)
 		if ok {
-			parts = append(parts, fmt.Sprintf("### Skill: %s\n\n%s", name, content))
+			if !first {
+				sb.WriteString("\n\n---\n\n")
+			}
+			fmt.Fprintf(&sb, "### Skill: %s\n\n%s", name, content)
+			first = false
 		}
 	}
 
-	return strings.Join(parts, "\n\n---\n\n")
+	return sb.String()
 }
 
 func (sl *SkillsLoader) BuildSkillsSummary() string {
@@ -231,23 +236,23 @@ func (sl *SkillsLoader) BuildSkillsSummary() string {
 		return ""
 	}
 
-	var lines []string
+	var sb strings.Builder
-	lines = append(lines, "<skills>")
+	sb.WriteString("<skills>")
 	for _, s := range allSkills {
 		escapedName := escapeXML(s.Name)
 		escapedDesc := escapeXML(s.Description)
 		escapedPath := escapeXML(s.Path)
 
-		lines = append(lines, fmt.Sprintf("  <skill>"))
+		sb.WriteString("\n  <skill>")
-		lines = append(lines, fmt.Sprintf("    <name>%s</name>", escapedName))
+		fmt.Fprintf(&sb, "\n    <name>%s</name>", escapedName)
-		lines = append(lines, fmt.Sprintf("    <description>%s</description>", escapedDesc))
+		fmt.Fprintf(&sb, "\n    <description>%s</description>", escapedDesc)
-		lines = append(lines, fmt.Sprintf("    <location>%s</location>", escapedPath))
+		fmt.Fprintf(&sb, "\n    <location>%s</location>", escapedPath)
-		lines = append(lines, fmt.Sprintf("    <source>%s</source>", s.Source))
+		fmt.Fprintf(&sb, "\n    <source>%s</source>", s.Source)
-		lines = append(lines, "  </skill>")
+		sb.WriteString("\n  </skill>")
 	}
-	lines = append(lines, "</skills>")
+	sb.WriteString("\n</skills>")
 
-	return strings.Join(lines, "\n")
+	return sb.String()
 }
 
 func (sl *SkillsLoader) getSkillMetadata(skillPath string) *SkillMetadata {

pkg/tools/web.go

@@ -70,19 +70,19 @@ func (p *BraveSearchProvider) Search(ctx context.Context, query string, count in
 		return fmt.Sprintf("No results for: %s", query), nil
 	}
 
-	var lines []string
+	var sb strings.Builder
-	lines = append(lines, fmt.Sprintf("Results for: %s", query))
+	fmt.Fprintf(&sb, "Results for: %s", query)
 	for i, item := range results {
 		if i >= count {
 			break
 		}
-		lines = append(lines, fmt.Sprintf("%d. %s\n   %s", i+1, item.Title, item.URL))
+		fmt.Fprintf(&sb, "\n%d. %s\n   %s", i+1, item.Title, item.URL)
 		if item.Description != "" {
-			lines = append(lines, fmt.Sprintf("   %s", item.Description))
+			fmt.Fprintf(&sb, "\n   %s", item.Description)
 		}
 	}
 
-	return strings.Join(lines, "\n"), nil
+	return sb.String(), nil
 }
 
 type TavilySearchProvider struct {
@@ -152,19 +152,19 @@ func (p *TavilySearchProvider) Search(ctx context.Context, query string, count i
 		return fmt.Sprintf("No results for: %s", query), nil
 	}
 
-	var lines []string
+	var sb strings.Builder
-	lines = append(lines, fmt.Sprintf("Results for: %s (via Tavily)", query))
+	fmt.Fprintf(&sb, "Results for: %s (via Tavily)", query)
 	for i, item := range results {
 		if i >= count {
 			break
 		}
-		lines = append(lines, fmt.Sprintf("%d. %s\n   %s", i+1, item.Title, item.URL))
+		fmt.Fprintf(&sb, "\n%d. %s\n   %s", i+1, item.Title, item.URL)
 		if item.Content != "" {
-			lines = append(lines, fmt.Sprintf("   %s", item.Content))
+			fmt.Fprintf(&sb, "\n   %s", item.Content)
 		}
 	}
 
-	return strings.Join(lines, "\n"), nil
+	return sb.String(), nil
 }
 
 type DuckDuckGoSearchProvider struct{}
@@ -208,17 +208,9 @@ func (p *DuckDuckGoSearchProvider) extractResults(html string, count int, query
 		return fmt.Sprintf("No results found or extraction failed. Query: %s", query), nil
 	}
 
-	var lines []string
+	var sb strings.Builder
-	lines = append(lines, fmt.Sprintf("Results for: %s (via DuckDuckGo)", query))
+	fmt.Fprintf(&sb, "Results for: %s (via DuckDuckGo)", query)
 
-	// Pre-compile snippet regex to run inside the loop
-	// We'll search for snippets relative to the link position or just globally if needed
-	// But simple global search for snippets might mismatch order.
-	// Since we only have the raw HTML string, let's just extract snippets globally and assume order matches (risky but simple for regex)
-	// Or better: Let's assume the snippet follows the link in the HTML
-
-	// A better regex approach: iterate through text and find matches in order
-	// But for now, let's grab all snippets too
 	reSnippet := regexp.MustCompile(`<a class="result__snippet[^"]*".*?>([\s\S]*?)</a>`)
 	snippetMatches := reSnippet.FindAllStringSubmatch(html, count+5)
 
@@ -239,19 +231,19 @@ func (p *DuckDuckGoSearchProvider) extractResults(html string, count int, query
 			}
 		}
 
-		lines = append(lines, fmt.Sprintf("%d. %s\n   %s", i+1, title, urlStr))
+		fmt.Fprintf(&sb, "\n%d. %s\n   %s", i+1, title, urlStr)
 
 		// Attempt to attach snippet if available and index aligns
 		if i < len(snippetMatches) {
 			snippet := stripTags(snippetMatches[i][1])
 			snippet = strings.TrimSpace(snippet)
 			if snippet != "" {
-				lines = append(lines, fmt.Sprintf("   %s", snippet))
+				fmt.Fprintf(&sb, "\n   %s", snippet)
 			}
 		}
 	}
 
-	return strings.Join(lines, "\n"), nil
+	return sb.String(), nil
 }
 
 func stripTags(content string) string {
@@ -605,13 +597,16 @@ func (t *WebFetchTool) extractText(htmlContent string) string {
 	result = re.ReplaceAllString(result, "\n\n")
 
 	lines := strings.Split(result, "\n")
-	var cleanLines []string
+	var sb strings.Builder
 	for _, line := range lines {
 		line = strings.TrimSpace(line)
 		if line != "" {
-			cleanLines = append(cleanLines, line)
+			if sb.Len() > 0 {
+				sb.WriteByte('\n')
+			}
+			sb.WriteString(line)
 		}
 	}
 
-	return strings.Join(cleanLines, "\n")
+	return sb.String()
 }