fix(engine): make no-op rollback side-effect free

[GhostXia]

Summary

• define rollback to the current active leaf as a pure no-op
• preserve updated_at, revision, and on-disk bytes for successful no-op retries
• document the persistence contract and add legacy-load regression coverage

Validation

• cargo test -p airp-core --lib chat_store::tests::rollback_to --locked -- --nocapture (4 passed)
• cargo test -p airp-core --lib domain::tests::rollback --locked -- --nocapture (4 passed)
• cargo fmt --all -- --check
• git diff --check

Closes #140

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Review details

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: eefb532c-d6cd-4b7f-9925-0b499bf67023

📥 Commits

Reviewing files that changed from the base of the PR and between f2bea56 and 8dab0ea.

📒 Files selected for processing (3)

• docs/audits/2026-08-13-PR-566-rollback-noop-audit.md
• engine/README.md
• engine/src/chat_store.rs

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[github-actions]

⚠️ Agent exploration runner failed

The exploration runner exited with a non-zero status. The actual report comment may be missing or partial.

• See the workflow run for logs.
• Download the agent-exploration-566 artifact for any partial report/trace files.

This is a non-blocking placeholder (workflow has continue-on-error: true); merge is not blocked. Investigate the failure if it persists.

[github-actions]

⚠️ Non-blocking (阶段 2 MVP): 此报告不阻塞 PR 合并。崩溃/数据损坏/安全问题需人工确认；可用性问题仅记录。

Agent Browser Exploration Report

Run ID: run-1786545873769
Trigger: pr-566
PR: 566
Started: 2026-08-12T14:44:33.769Z
Duration: 221236ms
LLM: deepseek-v4-flash

Summary

• Total tasks: 1
• Passed: 0
• Failed: 1
• Flaky: 0

Task: edit-branch-switch-refresh

Result: Failed

Description

前置：用 API 准备一个角色 + 一个有至少 2 轮对话的 session。

步骤提示：

1. 导航到 02-chat-space.html?character=&session=
2. 记录当前 history 的所有 message_ids 和 active_leaf（通过 /v1/chat/history）
3. 找到第一条 role=user 消息的 message_id
4. 调 PUT /v1/chat/message 编辑该用户消息 content 为 'I changed my question: what is the library policy on late returns?'
5. 由于编辑历史用户消息会触发分支语义（按 engine 当前实现：编辑 user 消息可能创建分支或原地替换；
   以 engine 实现为准），调 /v1/chat/history 确认当前 active path 状态
6. 如果 engine 支持分支（chat_store 有 branch_tree）：调 /v1/chat/branch/switch
   切换到原 active_leaf（编辑前的 leaf）
7. 在原分支继续发一条用户消息 'Thanks.', 等待 assistant 回复
8. 切换回新分支（编辑后的 leaf），发一条用户消息 'And the fines?', 等待 assistant 回复
9. 多次切换两个分支（至少 3 次来回），每次确认 history 只显示当前 active path
10. 刷新页面：await ctx.page.reload()
11. 再次调 /v1/chat/history
12. ASSERT: 当前 active_leaf 与刷新前一致
13. ASSERT: 当前 active path 的消息序列与刷新前一致
14. ASSERT: 另一分支的数据未被删除（切回另一分支验证其消息序列仍在）

Expected

编辑历史用户消息后建立的分支，与原分支共存；
多次切换后，刷新页面应保持当前 active path；
另一分支数据未被污染或删除。

Actual

Error: agent script failed after 3 revisions; last error:
Script validation failed (script NOT executed):

• JavaScript module syntax check failed: [stdin]:2 "active_leaf": "uuid", ^ SyntaxError: Unexpected token ':' at checkSyntax (node:internal/main/check_syntax:74:5) at node:internal/main/check_syntax:45:5 at Socket. (node:internal/process/execution:234:5) at Socket.emit (node:events:536:35) at endReadableNT (node:internal/streams/readable:1698:12) at process.processTicksAndRejections (node:internal/process/task_queues:82:21) Node.js v20.20.2
• Missing required module export: export async function run(ctx)

Fix these and re-output the complete script.
at generateAndRunScript (file:///home/runner/work/AIRP/AIRP/tools/agent-exploration/runner.mjs:470:17)
at process.processTicksAndRejections (node:internal/process/task_queues:95:5)
at async runTask (file:///home/runner/work/AIRP/AIRP/tools/agent-exploration/runner.mjs:336:26)
at async runTasks (file:///home/runner/work/AIRP/AIRP/tools/agent-exploration/runner.mjs:184:16)
at async main (file:///home/runner/work/AIRP/AIRP/tools/agent-exploration/runner.mjs:157:9)
at async file:///home/runner/work/AIRP/AIRP/tools/agent-exploration/runner.mjs:662:3

Evidence

• script: /home/runner/work/AIRP/AIRP/artifacts/agent-exploration/edit-branch-switch-refresh/agent-script-revision-2.mjs
• trace: /home/runner/work/AIRP/AIRP/artifacts/agent-exploration/edit-branch-switch-refresh/trace.zip

[github-actions]

⚠️ Agent exploration runner failed

The exploration runner exited with a non-zero status. The actual report comment may be missing or partial.

• See the workflow run for logs.
• Download the agent-exploration-566 artifact for any partial report/trace files.

This is a non-blocking placeholder (workflow has continue-on-error: true); merge is not blocked. Investigate the failure if it persists.

[github-actions]

⚠️ Non-blocking (阶段 2 MVP): 此报告不阻塞 PR 合并。崩溃/数据损坏/安全问题需人工确认；可用性问题仅记录。

Agent Browser Exploration Report

Run ID: run-1786547312605
Trigger: pr-566
PR: 566
Started: 2026-08-12T15:08:32.605Z
Duration: 216142ms
LLM: deepseek-v4-flash

Summary

• Total tasks: 1
• Passed: 0
• Failed: 1
• Flaky: 0

Task: edit-branch-switch-refresh

Result: Failed

Description

前置：用 API 准备一个角色 + 一个有至少 2 轮对话的 session。

步骤提示：

1. 导航到 02-chat-space.html?character=&session=
2. 记录当前 history 的所有 message_ids 和 active_leaf（通过 /v1/chat/history）
3. 找到第一条 role=user 消息的 message_id
4. 调 PUT /v1/chat/message 编辑该用户消息 content 为 'I changed my question: what is the library policy on late returns?'
5. 由于编辑历史用户消息会触发分支语义（按 engine 当前实现：编辑 user 消息可能创建分支或原地替换；
   以 engine 实现为准），调 /v1/chat/history 确认当前 active path 状态
6. 如果 engine 支持分支（chat_store 有 branch_tree）：调 /v1/chat/branch/switch
   切换到原 active_leaf（编辑前的 leaf）
7. 在原分支继续发一条用户消息 'Thanks.', 等待 assistant 回复
8. 切换回新分支（编辑后的 leaf），发一条用户消息 'And the fines?', 等待 assistant 回复
9. 多次切换两个分支（至少 3 次来回），每次确认 history 只显示当前 active path
10. 刷新页面：await ctx.page.reload()
11. 再次调 /v1/chat/history
12. ASSERT: 当前 active_leaf 与刷新前一致
13. ASSERT: 当前 active path 的消息序列与刷新前一致
14. ASSERT: 另一分支的数据未被删除（切回另一分支验证其消息序列仍在）

Expected

编辑历史用户消息后建立的分支，与原分支共存；
多次切换后，刷新页面应保持当前 active path；
另一分支数据未被污染或删除。

Actual

Error: agent script failed after 3 revisions; last error:
Script validation failed (script NOT executed):

• JavaScript module syntax check failed: [stdin]:6 if (backLeaf !== originalLeaf) { natural? } ^ SyntaxError: Unexpected token '}' at checkSyntax (node:internal/main/check_syntax:74:5) at node:internal/main/check_syntax:45:5 at Socket. (node:internal/process/execution:234:5) at Socket.emit (node:events:536:35) at endReadableNT (node:internal/streams/readable:1698:12) at process.processTicksAndRejections (node:internal/process/task_queues:82:21) Node.js v20.20.2
• Missing required module export: export async function run(ctx)

Fix these and re-output the complete script.
at generateAndRunScript (file:///home/runner/work/AIRP/AIRP/tools/agent-exploration/runner.mjs:470:17)
at process.processTicksAndRejections (node:internal/process/task_queues:95:5)
at async runTask (file:///home/runner/work/AIRP/AIRP/tools/agent-exploration/runner.mjs:336:26)
at async runTasks (file:///home/runner/work/AIRP/AIRP/tools/agent-exploration/runner.mjs:184:16)
at async main (file:///home/runner/work/AIRP/AIRP/tools/agent-exploration/runner.mjs:157:9)
at async file:///home/runner/work/AIRP/AIRP/tools/agent-exploration/runner.mjs:662:3

Evidence

• script: /home/runner/work/AIRP/AIRP/artifacts/agent-exploration/edit-branch-switch-refresh/agent-script-revision-2.mjs
• trace: /home/runner/work/AIRP/AIRP/artifacts/agent-exploration/edit-branch-switch-refresh/trace.zip

[github-actions]

⚠️ Agent exploration runner failed

The exploration runner exited with a non-zero status. The actual report comment may be missing or partial.

• See the workflow run for logs.
• Download the agent-exploration-566 artifact for any partial report/trace files.

This is a non-blocking placeholder (workflow has continue-on-error: true); merge is not blocked. Investigate the failure if it persists.

[github-actions]

⚠️ Non-blocking (阶段 2 MVP): 此报告不阻塞 PR 合并。崩溃/数据损坏/安全问题需人工确认；可用性问题仅记录。

Agent Browser Exploration Report

Run ID: run-1786610452846
Trigger: pr-566
PR: 566
Started: 2026-08-13T08:40:52.846Z
Duration: 169015ms
LLM: deepseek-v4-flash

Summary

• Total tasks: 1
• Passed: 0
• Failed: 1
• Flaky: 0

Task: edit-branch-switch-refresh

Result: Failed

Description

前置：用 API 准备一个角色 + 一个有至少 2 轮对话的 session。

步骤提示：

1. 导航到 02-chat-space.html?character=&session=
2. 记录当前 history 的所有 message_ids 和 active_leaf（通过 /v1/chat/history）
3. 找到第一条 role=user 消息的 message_id
4. 调 PUT /v1/chat/message 编辑该用户消息 content 为 'I changed my question: what is the library policy on late returns?'
5. 由于编辑历史用户消息会触发分支语义（按 engine 当前实现：编辑 user 消息可能创建分支或原地替换；
   以 engine 实现为准），调 /v1/chat/history 确认当前 active path 状态
6. 如果 engine 支持分支（chat_store 有 branch_tree）：调 /v1/chat/branch/switch
   切换到原 active_leaf（编辑前的 leaf）
7. 在原分支继续发一条用户消息 'Thanks.', 等待 assistant 回复
8. 切换回新分支（编辑后的 leaf），发一条用户消息 'And the fines?', 等待 assistant 回复
9. 多次切换两个分支（至少 3 次来回），每次确认 history 只显示当前 active path
10. 刷新页面：await ctx.page.reload()
11. 再次调 /v1/chat/history
12. ASSERT: 当前 active_leaf 与刷新前一致
13. ASSERT: 当前 active path 的消息序列与刷新前一致
14. ASSERT: 另一分支的数据未被删除（切回另一分支验证其消息序列仍在）

Expected

编辑历史用户消息后建立的分支，与原分支共存；
多次切换后，刷新页面应保持当前 active path；
另一分支数据未被污染或删除。

Actual

Error: agent script failed after 3 revisions; last error:
Error: ASSERT: user message id missing in history response
at Module.run (file:///home/runner/work/AIRP/AIRP/artifacts/agent-exploration/edit-branch-switch-refresh/agent-script-revision-2.mjs?t=1786610620133:33:30)
at async runTempScript (file:///home/runner/work/AIRP/AIRP/tools/agent-exploration/runner.mjs:624:5)
at async generateAndRunScript (file:///home/runner/work/AIRP/AIRP/tools/agent-exploration/runner.mjs:463:24)
at async runTask (file:///home/runner/work/AIRP/AIRP/tools/agent-exploration/runner.mjs:336:26)
at async runTasks (file:///home/runner/work/AIRP/AIRP/tools/agent-exploration/runner.mjs:184:16)
at async main (file:///home/runner/work/AIRP/AIRP/tools/agent-exploration/runner.mjs:157:9)
at async file:///home/runner/work/AIRP/AIRP/tools/agent-exploration/runner.mjs:662:3
at generateAndRunScript (file:///home/runner/work/AIRP/AIRP/tools/agent-exploration/runner.mjs:470:17)
at async runTask (file:///home/runner/work/AIRP/AIRP/tools/agent-exploration/runner.mjs:336:26)
at async runTasks (file:///home/runner/work/AIRP/AIRP/tools/agent-exploration/runner.mjs:184:16)
at async main (file:///home/runner/work/AIRP/AIRP/tools/agent-exploration/runner.mjs:157:9)
at async file:///home/runner/work/AIRP/AIRP/tools/agent-exploration/runner.mjs:662:3

Evidence

• script: /home/runner/work/AIRP/AIRP/artifacts/agent-exploration/edit-branch-switch-refresh/agent-script-revision-2.mjs
• trace: /home/runner/work/AIRP/AIRP/artifacts/agent-exploration/edit-branch-switch-refresh/trace.zip