fix(parser): 修复 bufio.Scanner token too long 错误 (#64)

## 问题
- 执行 rg 等命令时，如果匹配到 minified 文件，单行输出可能超过 10MB
- 旧实现使用 bufio.Scanner，遇到超长行会报错并中止整个解析
- 导致后续的 agent_message 无法读取，任务失败

## 修复
1. **parser.go**:
   - 移除 bufio.Scanner，改用 bufio.Reader + readLineWithLimit
   - 超长行（>10MB）会被跳过但继续处理后续事件
   - 添加 codexHeader 轻量级解析，只在 agent_message 时完整解析

2. **utils.go**:
   - 修复 logWriter 内存膨胀问题
   - 添加 writeLimited 方法限制缓冲区大小

3. **测试**:
   - parser_token_too_long_test.go: 验证超长行处理
   - log_writer_limit_test.go: 验证日志缓冲限制

## 测试结果
- ✅ TestParseJSONStream_SkipsOverlongLineAndContinues
- ✅ TestLogWriterWriteLimitsBuffer
- ✅ 完整测试套件通过

Fixes #64

Generated with swe-agent-bot

Co-Authored-By: swe-agent-bot <agent@swe-agent.ai>

codeagent-wrapper/utils.go

@@ -78,6 +78,7 @@ type logWriter struct {
 	prefix string
 	maxLen int
 	buf    bytes.Buffer
+	dropped bool
 }
 
 func newLogWriter(prefix string, maxLen int) *logWriter {
@@ -94,12 +95,12 @@ func (lw *logWriter) Write(p []byte) (int, error) {
 	total := len(p)
 	for len(p) > 0 {
 		if idx := bytes.IndexByte(p, '\n'); idx >= 0 {
-			lw.buf.Write(p[:idx])
+			lw.writeLimited(p[:idx])
 			lw.logLine(true)
 			p = p[idx+1:]
 			continue
 		}
-		lw.buf.Write(p)
+		lw.writeLimited(p)
 		break
 	}
 	return total, nil
@@ -117,21 +118,53 @@ func (lw *logWriter) logLine(force bool) {
 		return
 	}
 	line := lw.buf.String()
+	dropped := lw.dropped
+	lw.dropped = false
 	lw.buf.Reset()
 	if line == "" && !force {
 		return
 	}
-	if lw.maxLen > 0 && len(line) > lw.maxLen {
-		cutoff := lw.maxLen
-		if cutoff > 3 {
-			line = line[:cutoff-3] + "..."
-		} else {
-			line = line[:cutoff]
+	if lw.maxLen > 0 {
+		if dropped {
+			if lw.maxLen > 3 {
+				line = line[:min(len(line), lw.maxLen-3)] + "..."
+			} else {
+				line = line[:min(len(line), lw.maxLen)]
+			}
+		} else if len(line) > lw.maxLen {
+			cutoff := lw.maxLen
+			if cutoff > 3 {
+				line = line[:cutoff-3] + "..."
+			} else {
+				line = line[:cutoff]
+			}
 		}
 	}
 	logInfo(lw.prefix + line)
 }
 
+func (lw *logWriter) writeLimited(p []byte) {
+	if lw == nil || len(p) == 0 {
+		return
+	}
+	if lw.maxLen <= 0 {
+		lw.buf.Write(p)
+		return
+	}
+
+	remaining := lw.maxLen - lw.buf.Len()
+	if remaining <= 0 {
+		lw.dropped = true
+		return
+	}
+	if len(p) <= remaining {
+		lw.buf.Write(p)
+		return
+	}
+	lw.buf.Write(p[:remaining])
+	lw.dropped = true
+}
+
 type tailBuffer struct {
 	limit int
 	data  []byte