fix(runtime): preserve Codex transcript turn boundaries

[kingfs]

Summary

Preserve boundaries between consecutive Codex interactive turns in the runtime transcript.

The interactive session now keeps its buffered text writer and inserts a newline before a subsequent turn when the previous output did not end with one. This
prevents output from adjacent turns from being concatenated while avoiding redundant separators when a newline is already present.

Testing

• npm test
  • 16 test files passed
  • 143 tests passed
• npm run typecheck
• git diff --check origin/main..HEAD

Checklist

• Documentation updated when behavior or configuration changed. No documentation update is required because this is an internal transcript formatting fix
  with no configuration or interface changes.
• Tests added or updated for user-visible behavior.
• No secrets, private endpoints, internal certificates, or local runtime state included.

[monkeyscan]

PR Title: fix(runtime): preserve Codex transcript turn bound...

Commit: 27b3f67

本次PR修复了Codex交互式会话中多轮对话时transcript缺少turn boundary的问题。主要变更：将BufferedTextWriter持久化为类字段，新增turnCount计数器，并在第二轮及以后的runHumanMessage调用时执行beginTurn()，在上一轮输出末尾追加换行符以实现回合分隔。测试新增了transcript字段的断言验证。经审查，变更逻辑自洽，没有发现引入安全、正确性或回归风险的问题。

[monkeyscan]

PR Title: fix(runtime): preserve Codex transcript turn bound...

Commit: 9e08774

本次 PR 仅修改了 runtime/javascript/test/runtime.e2e.test.ts，新增一个 E2E 测试用例 "preserves turn boundaries across interactive Codex messages"。

该测试通过 runStreamCommand 模拟交互式 Codex 会话，向 stdin 依次发送 start、human_message（"first"）、human_message（"second"）和 eof 帧，然后捕获 stdout 输出并断言最终 result 帧的 transcript 字段正确保留了两次消息的转录边界（{"input":"first"}\n{"input":"second"}）。

测试覆盖了前序 fix commit 中修复的 Codex 交互式消息 turn boundary 丢失问题。测试逻辑与 stream.ts、interactive.ts 及 runners/codex.ts 的实现一致：每轮 human_message 触发 runStreamed，BufferedTextWriter 在轮次切换时通过 beginTurn() 插入换行，最终 transcript 以换行分隔各轮输出。断言聚焦于最终结果帧的 transcript，符合该测试的回归防护目标。

整体评估：变更范围单一、意图明确，测试代码结构清晰，未发现正确性、安全性或可维护性方面的可执行问题。