feat(runtime): derive managed mutations from accepted content

[zhiiw]

Summary

• compute managed Write/Edit as pure transforms over immutable accepted-tree content
• keep all provider arguments under Runtime ownership
• expose only an immutable mutation result proof to the workspace owner
• normalize deterministic transform failures into no-effect operation evidence

This stacked slice does not create or accept a Git candidate. The next slice connects its proof to the durable candidate receipt owner and apache#3741 successor transaction.

中文说明

本 PR 只建立纯变换边界：Runtime 使用自己的原始 Write/Edit 参数与 accepted tree 的 immutable base content 计算结果。Host 无权返回完整 executionArgs，也不能改写 content/old_string/new_string。它尚不创建 candidate、推进 head 或接产品消费者。

[zhiiw]

Superseded by the rebuilt delivery stack #40 -> #41 -> #42. This extraction PR remains available as implementation and review history; no validated logic was discarded.

中文说明

该 extraction PR 已由从最新 main 重建的组合交付栈 #40 → #41 → #42 替代。这里仍保留实现与审查历史，已验证逻辑没有被丢弃。