fix(agent-runtime): persist evidence ledger

[zvzuola]

Summary

Persist EvidenceLedger events across session unloads, restarts, and restores to prevent long-running tasks from losing checkpoints, compression evidence, and partial subagent results.

The ledger is stored as a versioned evidence-ledger.json sidecar under the resolved session directory.

Type and Areas

Type: Bug fix / reliability

Areas: Rust core, Agent Runtime, session persistence, remote workspace

Motivation / Impact

Previously, EvidenceLedger existed only in process memory. When a session was unloaded or the host restarted, the ledger was lost. This could cause long-running tasks to lose important execution evidence and drift away from their original objective.

This change:

• Persists durable session evidence to a versioned JSON sidecar.
• Uses session-level serialization, cross-process file locking, and strict atomic replacement.
• Makes event appends idempotent by event_id.
• Rejects conflicting payloads for duplicate event IDs.
• Loads and validates the ledger before publishing restored runtime state.
• Preserves the original sidecar when the data is corrupt, from a newer schema, or belongs to another session.
• Keeps legacy payloads readable through additive defaults and unknown-enum fallbacks.
• Publishes evidence to in-memory state only after successful persistence.
• Makes checkpoint persistence fail closed for mutating Bash, file, and Git tools.
• Persists partial subagent timeout evidence while retaining already-produced partial results if persistence fails.
• Uses the resolved remote session mirror for remote workspaces instead of reusing controller-side paths.

No new user-facing strings, locale changes, or UI changes are required.

Verification

• cargo check --locked -p bitfun-agent-runtime --no-default-features --features agent-runtime — passed.
• cargo test --locked -p bitfun-agent-runtime --no-default-features --features agent-runtime --lib evidence_ledger — 11 passed.
• cargo test --locked -p bitfun-core --no-default-features --features agent-runtime --lib evidence_ledger — 4 passed.
• cargo test --locked -p bitfun-core --no-default-features --features agent-runtime --lib concurrent_evidence_appends_keep_disk_and_memory_complete — passed.
• cargo test --locked -p bitfun-core --no-default-features --features agent-runtime,remote-workspace --lib remote_workspace_evidence_uses_the_resolved_session_mirror — passed.
• cargo check --locked -p bitfun-core --no-default-features --features product-full — passed.
• pnpm run check:core-boundaries — passed.
• pnpm run fmt:rs — passed.
• git diff --check — passed.

The remote workspace scenario was exercised. Remote control, Peer Device Mode, and Detached Dispatch protocols were not changed by this PR and were not modified in the tests.

Reviewer Notes

• The persistence format is currently schema version 1.
• The sidecar is created only for durable sessions; transient sessions retain their existing in-memory behavior.
• Restore is fail-closed for invalid or incompatible ledger data and does not delete or overwrite the original sidecar.
• Concurrent appends are serialized in-process and protected across processes by the JSON file lock.
• Existing repository feature-conditional warnings remain, but all targeted tests and checks pass.

Checklist

• This PR is focused and does not include secrets, temporary prompts, generated scratch files, or unrelated artifacts.
• Relevant verification is recorded above.
• User-facing strings, docs, and locales are updated where applicable.

[limityan]

需要修改：回退会话后，已撤销的证据会在重启后重新出现

发生场景

1. 某个会话 turn 产生了文件修改前的 checkpoint、失败命令，或 subagent 的部分结果。
2. 用户把会话回退到这个 turn 之前，表示这些后续执行已经被撤销。
3. 用户关闭并重新打开会话，或应用重启后恢复该会话。

当前行为

恢复代码会正确隐藏回退点之后的对话 turn，但随后仍会从 evidence-ledger.json 加载全部历史证据。永久提交回退时，代码也只删除对话 turn、上下文快照和压缩产物，没有同步删除被回退 turn 对应的 ledger 记录。

造成的后果

重启后，已经被用户撤销的文件、失败命令和 subagent 结果会再次进入上下文压缩与 Deep Review。系统会把旧工作误认为当前事实，可能让 Agent 继续处理已经撤销的文件或问题。换句话说：界面中的会话已经回退，但 Agent 使用的证据没有一起回退。

修复要求

• staged revert 和永久回退都应按仍然保留的 turn ID，同步裁剪磁盘 sidecar 与内存 ledger。
• 恢复会话时，只应发布当前可见 turn 对应的证据。
• 增加回归测试：先产生 evidence，再 rollback，随后 unload/restore，确认 compression contract 不再包含被撤销 turn 的证据。

该问题会破坏本 PR 要保证的恢复一致性，因此修复前建议不要合并。