feat(runtime-host): prepare Gitoxide mutation candidates

[zhiiw]

Summary

Introduce the Gitoxide-owned immutable mutation candidate used by managed Write/Edit.

This Draft is stacked on the rebuilt successor authority. It carries the short-lived Gitoxide helper/data-plane prerequisites because the final delivery will be rebuilt after the stack lands.

Primary invariant

A captured mutation may publish only an operation-scoped candidate ref and durable receipt. It cannot advance accepted workspace truth.

• Owner: Runtime Host Gitoxide candidate authority.
• Atomic boundary: one Gitoxide ref transaction publishes the deterministic successor directly to the candidate ref from a frozen accepted base.
• Failure state: base/ref/receipt mismatch fails closed; accepted ref and SQLite head are unchanged.
• Recovery: ref-only and receipt-complete states converge by exact retry; a real child-process kill after ref publication is covered.

Scope

• pure immutable-tree successor construction through the short-lived helper;
• opaque owner-bound candidate capability;
• deterministic ref and strict durable receipt;
• exact reopen/retry and tamper rejection;
• three-platform real-helper CI, including process-kill recovery.

Not claimed

• No SQLite acceptance or accepted-ref promotion in this PR.
• No Write/Edit production composition in this PR.
• No M3 behavior.

中文说明

摘要

本 Draft 引入 managed Write/Edit 使用的 Gitoxide immutable mutation candidate owner，并叠加在重建版 successor authority 上。最终交付仍会在前置合并后从最新 main 重建。

主要不变量

一次 capture 只能发布 operation 专属 candidate ref 和严格 durable receipt，绝不能推进 accepted workspace truth。

• Owner： Runtime Host Gitoxide candidate authority。
• 原子边界： 单次 Gitoxide ref transaction 从冻结的 accepted base 直接发布确定性 successor 到 candidate ref。
• 失败状态： base/ref/receipt 任一不匹配都 fail closed；accepted ref 与 SQLite head 不变。
• 恢复： ref-only 与 receipt-complete 状态可由 exact retry 收敛；真实子进程在 ref 发布后被杀的恢复测试已覆盖。

范围

• 短生命周期 helper 从 immutable tree 构造纯 successor；
• owner-bound opaque candidate capability；
• 确定性 ref、严格 durable receipt、重开与篡改拒绝；
• 三平台真实 helper CI 和 process-kill recovery。

本 PR 不负责 SQLite acceptance、accepted-ref promotion、Write/Edit 生产组合或 M3。

[zhiiw]

Closed as an obsolete extraction/integration slice. The current delivery path is the merged Gitoxide foundation followed by #40 -> #41 -> #42. This PR remains available as design and implementation history.

中文说明

该 PR 属于旧 extraction/integration 栈，现已失去独立合并价值。当前交付路径是已合并的 Gitoxide 基础，然后依次审查 #40 → #41 → #42。这里继续保留设计、实现与审查历史。