feat(runtime): bind continuation to accepted Gitoxide workspace heads

[zhiiw]

Summary

Bind safe-boundary continuation to the exact accepted Gitoxide workspace head and prove that Host death does not replay an accepted Write/Edit or provider call.

This combines the old continuation extraction slice #39 into the final layer above #40 and #41.

Primary invariant

A continuation may start only when immutable Runtime history and immutable workspace history identify the same causal boundary: source run high-water, workspace epoch, execution profile, and accepted Git head.

• Owner: Runtime owns continuation lineage and event high-water; the managed Session owner supplies the exact accepted workspace boundary.
• Atomic boundary: continuation-start T1 binds the new Run to the authenticated source ledger prefix and workspace head before execution resumes.
• Failure states: missing, stale, mismatched, cyclic, or unverifiable evidence parks the continuation. There is no silent downgrade to legacy resume.
• Rollback/recovery: a started continuation is reconstructed from durable facts; accepted Write/Edit and provider results are adopted rather than replayed.

Scope

• workspace-bound continuation envelope and strict validation
• continuation lineage v2 binding
• Session Manager admission and lifecycle wiring
• exact accepted-head observation from the Gitoxide managed Session owner
• Host-kill/restart crash tests for no provider replay

Verification

• Core, Storage, Runtime, and Runtime Host builds pass.
• Runtime continuation suite: 16 passed locally.
• Six production-shaped Gitoxide helper/Host tests are explicitly environment-gated locally; they were not counted as passes. Building the real helper on this machine is blocked by a missing MSVC linker, not by source compilation.
• git diff --check passes.

Stack: #40 -> #41 -> this PR.

中文说明

摘要

本 PR 将 safe-boundary continuation 绑定到精确的 accepted Gitoxide workspace head，并证明 Host 崩溃后不会重放已经接受的 Write/Edit 或 provider 调用。它把旧 #39 合并为 #40、#41 之上的最终一层。

主要不变量

只有 immutable Runtime history 与 immutable workspace history 指向同一个 causal boundary 时，continuation 才能启动：source run high-water、workspace epoch、execution profile 与 accepted Git head 必须全部一致。

• Owner： Runtime 拥有 continuation lineage 与 event high-water；managed Session owner 提供精确的 accepted workspace boundary。
• 原子边界： continuation-start T1 在恢复执行前，把新 Run 绑定到经过认证的 source ledger prefix 与 workspace head。
• 失败状态： evidence 缺失、过期、不匹配、成环或不可验证时一律 park；不会静默降级到 legacy resume。
• 恢复方式： 已启动的 continuation 从 durable facts 重建；已接受的 Write/Edit 与 provider result 只 adopt，不重放。

本地四个 workspace 构建通过，Runtime continuation 测试 16 项通过。六个真实 Gitoxide helper/Host 用例因本机缺少可执行 helper 而明确 skip，没有冒充通过；本机 Rust 构建被缺失的 MSVC linker 阻塞。git diff --check 通过。

栈顺序：#40 → #41 → 本 PR。