feat(runtime-host): compose packaged Gitoxide managed sessions

[zhiiw]

Summary

Compose the reviewed Gitoxide Write/Edit authority into a packaged, owner-bound managed Session path.

This combines extraction slices #36-#38. Its base is #40, so the diff contains only Session ownership, packaged-helper release authority, and production Host composition.

Primary invariant

A managed Session can use Gitoxide Write/Edit only when the Host owns the exact admitted helper artifact and exact imported source epoch; development or PATH-discovered executables cannot self-authorize the profile.

• Owner: packaged-resource admission owns helper identity; the Runtime Host owns Session composition and lifetime.
• Atomic boundary: source import and baseline acceptance establish the immutable Session epoch before Write/Edit is exposed.
• Failure states: missing or mismatched helper authority makes the managed profile unavailable; there is no fallback to system Git or attached-checkout mutation.
• Rollback/recovery: exact durable baseline/import receipts are reused; mismatched source or artifact identity fails closed.

Scope

• Gitoxide managed Session owner
• packaged helper preparation and release verification
• Runtime Host composition for owner-bound managed sessions
• merged execution-profile digest and model-connection contracts

Verification

• Runtime Host builds against the merged mainline authorities.
• Focused managed-session tests are present; real-helper cases are environment-gated locally and run in the release/recovery lanes.
• git diff --check passes.

Stack: #40 -> this PR -> continuation PR.

中文说明

摘要

本 PR 把已审查的 Gitoxide Write/Edit authority 接入一个由 Host 所有、可打包发布的 managed Session 路径，并合并旧的 #36-#38。它以 #40 为 base，因此 diff 只包含 Session owner、packaged helper release authority 与 production Host composition。

主要不变量

只有 Host 持有精确的已准入 helper artifact，并且 source 已导入为精确的 workspace epoch 时，managed Session 才能使用 Gitoxide Write/Edit。开发态 executable、PATH 中的 Git 或调用者自报路径都不能自行获得此能力。

• Owner： packaged-resource admission 拥有 helper identity；Runtime Host 拥有 Session composition 与生命周期。
• 原子边界： source import 和 baseline acceptance 在暴露 Write/Edit 前建立 immutable Session epoch。
• 失败状态： helper authority 缺失或不匹配时 profile 明确 unavailable；不回退到系统 Git 或 attached checkout mutation。
• 恢复方式： 精确复用 durable baseline/import evidence；source 或 artifact identity 漂移则 fail closed。

本 PR 暂保持 Draft。栈顺序为：#40 → 本 PR → continuation PR。