fix(kun): keep token economy from rewriting history

[musnows]

中文

变更

• 将 token economy 的 tool result 压缩限制到当前 turn，避免改写旧历史。
• 为 request history hygiene 增加 currentTurnId scope，并在 agent loop 中传入当前 turn。
• 补充测试覆盖旧 turn 历史保持原样、当前 turn 仍可被压缩。

原因

历史记录压缩如果每轮改写旧 tool result，会让已进入请求历史的前缀不再稳定，破坏 provider prompt cache 命中。这个 PR 只修复历史压缩作用域，不包含 Read 工具多模态注入修复。

验证

• npm --prefix kun test -- token-economy.test.ts request-history-hygiene.test.ts
• npm --prefix kun test -- loop.test.ts -t "uses compact tool history for model requests without mutating persisted results|bounds tool history for model requests even when token economy is disabled"
• npm --prefix kun run build

English

Changes

• Limit token economy tool-result compression to the current turn.
• Add a currentTurnId scope to request history hygiene and pass it from the agent loop.
• Add tests that keep previous-turn history unchanged while still allowing current-turn compression.

Why

Rewriting historical tool results changes the stable request prefix between turns and can invalidate provider prompt-cache hits. This PR only fixes the history-compression scope and intentionally excludes the multimodal Read tool fix.

Validation

• npm --prefix kun test -- token-economy.test.ts request-history-hygiene.test.ts
• npm --prefix kun test -- loop.test.ts -t "uses compact tool history for model requests without mutating persisted results|bounds tool history for model requests even when token economy is disabled"
• npm --prefix kun run build