fix(runtime): abort foreground subagent turns

[musnows]

Summary

• Abort foreground delegated subagent turns when the parent turn is interrupted.
• Keep detached/background subagents isolated from parent stop signals, while logging that parent aborts are ignored.
• Add interrupt diagnostics for main turns, foreground subagents, and detached subagent cancellation paths.

Fixes #782

Changes

• Bridge the parent delegation signal to the foreground child turn service so the child model stream receives abort promptly.
• Preserve detached subagent behavior by keeping the independent background abort controller and logging ignored parent aborts.
• Add regression coverage for main-agent interrupt, foreground subagent interrupt, and detached subagent non-interruption.

Tests

• npm --prefix kun run test -- src/delegation/child-agent-executor.test.ts src/loop/agent-loop.test.ts
• npm --prefix kun run typecheck

[XingYu-Zhong]

暂不合入，具体原因：

• PR 当前是 draft。
• GitHub mergeability 是 CONFLICTING，不能直接合入 develop。
• 分支里还带了两条和本 PR 主题无关的 CI 提交：ci(pr): add pull request checks、ci(pr): request changes on check failure。这会扩大 diff，建议 rebase/squash 后只保留 subagent interrupt 相关改动。
• 代码里新增了多处 console.warn 调试日志（foreground/detached subagent abort、turn interrupt），这些如果要保留应改成项目现有 logger/事件体系并控制噪声；否则合前应移除。

功能方向可以继续：父 turn abort 前台 subagent、detached child 独立取消信号这两点都有价值。请先标记 ready、解决冲突、移除无关 CI 提交和临时日志后再 review/merge。

[XingYu-Zhong]

Reviewed via Codex triage; approved for merge.