fix(backend): create_commit 直接引用经典空树 SHA（W1-C2 #165，ADR-0054） by randypanding · Pull Request #2 · Cloudbird-Software/arbiter

randypanding · 2026-08-21T15:51:33Z

动机

W1-C3 AC-1 e2e 演习（陌生 agent，卡 .github#206）抓出：GitHubRefBackend.create_commit 先 POST /git/trees 空 body 建空树，GitHub 对空树创建一律 422 Invalid tree info（{}/tree:[]/base_tree 姿势全拒）——租约创建在真实 API 上从未成功过。单测全走 LocalGitBackend 故未暴露（conductor run 32493680834 实证，fail-closed ABORT 语义正确工作：拒绝+不绕过）。

变更

create_commit 删除 /git/trees 调用，直接以经典空树 SHA 4b825dc… 为 tree 调 POST /git/commits（租约元数据全在 commit message，无需树内容）
新增 tests/test_github_backend_wire.py（3 例，HTTP 请求形状层回归锁定：trees 零调用、tree=常量、parent 透传、常量值本体断言）

验证

本地全量 unittest：72 tests OK（69+3）
修复合入后由主代理在 .github#206 重投 /claim 完成 e2e 闭环（租约 ref 实存验证）

AC 映射（#165 AC-2/AC-5 补强）

真实 GitHub 后端的 CAS 链路至此才有实证；fail-closed 行为已被 e2e 负向验证（infra=ABORT 非绕过）。

回滚：revert 本 PR（内核其余路径零改动）。

Summary by CodeRabbit

Bug 修复
- 优化 GitHub 提交创建流程，创建空提交时更加稳定可靠。
- 避免不必要的空树创建请求，减少 API 调用并提升处理效率。
- 修复并验证带有父提交和无父提交两种场景下的提交数据传递。

…b 一律 422（e2e .github#206 实测，conductor run 32493680834）(1/2)

coderabbitai · 2026-08-21T15:51:58Z

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Reviewing files that changed from the base of the PR and between 2f344cd and 50ec39e.

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arbiter/backend.py
tests/test_github_backend_wire.py

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📝 Walkthrough

Walkthrough

Changes

GitHub 空提交创建

Layer / File(s)	Summary
空提交请求与回归验证 `arbiter/backend.py`, `tests/test_github_backend_wire.py`	`GitHubRefBackend.create_commit` 使用固定的 `EMPTY_TREE_SHA` 调用 `/git/commits`，不再调用 `/git/trees`。测试覆盖无父提交、有父提交、请求调用次数及 canonical 常量值。

Suggested labels: bug

Merge Risk: ⚪ Minimal · up to 50ec3

This change uses the GitHub-compatible classic empty-tree SHA when creating commits and adds regression coverage for the request shape; no actionable merge-blocking risk remains beyond normal checks and review.

🚥 Pre-merge checks | ✅ 1 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Title check	⚠️ Warning	标题准确描述了修复内容，并使用了有效的 Conventional Commits 前缀，但长度为 61 个字符，超过 50 字符限制。	将标题缩短至 50 个字符以内，同时保留有效前缀和核心修复内容。

✅ Passed checks (1 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.

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Commit unit tests in branch fix-empty-tree

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qodo-code-review · 2026-08-21T15:52:07Z

PR Summary by Qodo

Fix GitHubRefBackend create_commit to use canonical empty tree SHA

🐞 Bug fix 🧪 Tests 🕐 10-20 Minutes

AI Description

• Fix GitHub create_commit by removing failing empty-tree /git/trees call
• Always create commits using Git’s canonical empty tree SHA
• Add wire-level tests to lock HTTP request shape and parent passthrough

Diagram

graph TD
  A["GitHubRefBackend.create_commit"] --> B["EMPTY_TREE_SHA constant"] --> C["GitHub API /git/commits"]
  A --> C

High-Level Assessment

The following are alternative approaches to this PR:

1. Use parent commit’s tree when parent is provided

➕ Avoids relying on a magic constant
➕ Ensures tree is always known-valid in GitHub
➖ Doesn’t solve the no-parent case (new lease) by itself
➖ Couples lease commit creation to repository state more than necessary

2. Create a minimal tree with a placeholder blob

➕ Avoids empty-tree edge case entirely
➕ Tree SHA is derived from content rather than a hardcoded constant
➖ Introduces unnecessary repo content semantics and storage
➖ More API calls (blobs/trees) and more failure modes

Recommendation: Keep the PR’s approach: using git’s canonical empty-tree SHA is the simplest and most stable fix given that lease/ledger metadata is stored entirely in the commit message. It removes a GitHub API call path that is known to fail (422) and is now protected by wire-level regression tests.

Files changed (2) +74 / -8

Bug fix (1) +8 / -8

backend.pyUse canonical empty-tree SHA for GitHubRefBackend.create_commit +8/-8

Use canonical empty-tree SHA for GitHubRefBackend.create_commit

• Stops calling POST /git/trees to create an empty tree (GitHub rejects this with 422). Introduces EMPTY_TREE_SHA and always posts commits with that tree; parent commit SHA is still passed through when provided.

arbiter/backend.py

Tests (1) +66 / -0

test_github_backend_wire.pyAdd wire regression tests for GitHubRefBackend create_commit +66/-0

Add wire regression tests for GitHubRefBackend create_commit

• Adds three unittest cases that mock _request to assert create_commit makes exactly one POST to /git/commits, uses the canonical empty-tree SHA, and correctly passes parents when provided. Also pins the constant value to prevent accidental drift without real API evidence.

tests/test_github_backend_wire.py

qodo-code-review · 2026-08-21T15:53:57Z

Code Review by Qodo

🐞 Bugs (1) 📘 Rule violations (0) 📜 Skill insights (0)

1. Parent 分支未锁请求形状 🐞 Bug ⚙ Maintainability

Description

tests/test_github_backend_wire.py 的 parent 用例未断言只发生一次请求、且请求路径必须是 /git/commits，因此未来若仅在 parent
分支回归引入额外调用（例如再调用 /git/trees）可能不会被该用例稳定捕获。该测试文件的意图是“HTTP 请求形状回归锁定”，建议对 parent 场景同样加上请求次数与路径断言。

Code

tests/test_github_backend_wire.py[R46-49]

+        def fake_request(method, path, body=None):
+            calls.append((method, path, body))
+            return 201, {"sha": "beef"}
+

Evidence

parent 场景测试目前对 _request 的 fake 实现对任意 path 都返回 201，且用例未断言请求次数/路径；而生产代码在 if parent: 分支会改写
body（未来也可能被人扩展为额外请求），因此该用例没有把“请求形状”在 parent 分支上锁死。

tests/test_github_backend_wire.py[43-55]
arbiter/backend.py[124-133]

Agent prompt

The issue below was found during a code review. Follow the provided context and guidance below and implement a solution

## Issue description
`test_create_commit_with_parent` 目前只断言了 `parents` 透传，但没有锁定：
- 仅一次 HTTP 调用
- 调用路径必须是 `.../git/commits`
- 不允许任何额外调用（例如回归引入 `/git/trees`）

这与该文件的“请求形状回归测试”目标不完全一致。

## Issue Context
`create_commit` 存在 `if parent:` 分支（parent 场景与非 parent 场景可能在未来被人改出差异），因此需要在 parent 用例里也做同等强度的 wire-level 断言。

## Fix Focus Areas
- tests/test_github_backend_wire.py[43-55]
- arbiter/backend.py[126-129]

## Suggested change
在 `test_create_commit_with_parent` 中：
1) 让 `fake_request` 对非 `/git/commits` 的调用直接 `AssertionError`（与第一个用例一致）。
2) 在调用后断言 `len(calls) == 1`。
3) 断言 `method == "POST"` 且 `path.endswith("/git/commits")`。
4) 同时断言 `body["tree"] == GitHubRefBackend.EMPTY_TREE_SHA`，确保 parent 场景也使用空树常量。

ⓘ Copy this prompt and use it to remediate the issue with your preferred AI generation tools

Context sources

✅ Web pages:

🌐 GitHub v3 API - how do I create the initial commit in a repository?

🌐 How can I use the Github API to push an empty commit

🌐 fix(push_repo_memory): seed new memory branches via GitHub API to satisfy signed-commit rules

+2 more

Review mode: ⚖️ Balanced: 该变更修改 GitHub 后端真实 API 的提交链路并引入固定协议常量，虽逻辑集中且有回归测试，但属于有行为和外部契约影响的风险变更，需完整单次审查。

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Copilot

Pull request overview

该 PR 修复 GitHubRefBackend.create_commit 在真实 GitHub Git Data API 上无法创建“空树”的问题：不再调用 POST /git/trees 试图创建空树，而是直接使用 Git 的经典空树 SHA 作为 commit 的 tree，从而让租约/台账的 commit 能在真实 API 上成功落地（元数据仍仅存于 commit message）。

Changes:

GitHubRefBackend.create_commit 移除 /git/trees 调用，改为使用常量 EMPTY_TREE_SHA 直接创建 commit。
新增 wire-level 回归测试，锁定 create_commit 的 HTTP 请求形状（确保不再回归到 /git/trees）。

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
`arbiter/backend.py`	为 GitHub 后端引入经典空树 SHA 常量，并让 `create_commit` 直接引用该 tree 创建 commit。
`tests/test_github_backend_wire.py`	新增对 `GitHubRefBackend.create_commit` 的请求形状回归测试（mock `_request`）。

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+import unittest
+from unittest.mock import patch
+
+from arbiter.backend import GitHubRefBackend


qodo-code-review · 2026-08-21T15:53:59Z

+        def fake_request(method, path, body=None):
+            calls.append((method, path, body))
+            return 201, {"sha": "beef"}
+


1. Parent 分支未锁请求形状 🐞 Bug ⚙ Maintainability

tests/test_github_backend_wire.py 的 parent 用例未断言只发生一次请求、且请求路径必须是 /git/commits，因此未来若仅在 parent 分支回归引入额外调用（例如再调用 /git/trees）可能不会被该用例稳定捕获。该测试文件的意图是“HTTP 请求形状回归锁定”，建议对 parent 场景同样加上请求次数与路径断言。

Agent Prompt

## Issue description `test_create_commit_with_parent` 目前只断言了 `parents` 透传，但没有锁定： - 仅一次 HTTP 调用 - 调用路径必须是 `.../git/commits` - 不允许任何额外调用（例如回归引入 `/git/trees`）这与该文件的“请求形状回归测试”目标不完全一致。 ## Issue Context `create_commit` 存在 `if parent:` 分支（parent 场景与非 parent 场景可能在未来被人改出差异），因此需要在 parent 用例里也做同等强度的 wire-level 断言。 ## Fix Focus Areas - tests/test_github_backend_wire.py[43-55] - arbiter/backend.py[126-129] ## Suggested change 在 `test_create_commit_with_parent` 中： 1) 让 `fake_request` 对非 `/git/commits` 的调用直接 `AssertionError`（与第一个用例一致）。 2) 在调用后断言 `len(calls) == 1`。 3) 断言 `method == "POST"` 且 `path.endswith("/git/commits")`。 4) 同时断言 `body["tree"] == GitHubRefBackend.EMPTY_TREE_SHA`，确保 parent 场景也使用空树常量。

ⓘ Copy this prompt and use it to remediate the issue with your preferred AI generation tools

清偿项（全部行为保持，裁决语义/退出码/错误通道零变化）： - kernel.adjudicate：删除防重放段无操作的 try/except InfraError: raise 纯透传包装（异常本就由函数级 infra 通道统一上报）；防重放语义（seen ref + 台账）与 CasConflict→noop/replay-detected 路径逐字节不变 - kernel.EXIT_CODE：改由 EXIT_ALLOW/EXIT_DENY/EXIT_INFRA 常量组装，消除字面量双写（原三常量从未被引用，属死代码） - backend.LocalGitBackend：4 处重复的 subprocess.run(git -C …) 样板收敛为 _exec_git 单一入口；各调用方的异常包装与报错文案逐字保留（"git 子进程失败"/"git rev-parse 失败"两通道不合并） - 魔法常量具名化：timeout=30×4 → GIT_TIMEOUT_SECONDS；重试 3 次/0.15s → LOCK_RETRY_MAX_ATTEMPTS / LOCK_RETRY_SLEEP_SECONDS - 函数内 import（time / urllib.request|error|parse）上提至模块顶部（backend.py 是静态扫描白名单中的唯一网络模块，tests/test_no_llm.py 不受限）不动项：#2 空树 SHA 链路与 _quote_ref_path refs/ 剥离逻辑零触碰； capabilities.yaml / AGENTS.md / ci.yml / README / tests 断言数量不减。验证：python -m py_compile arbiter/*.py ✓； python -m unittest discover -s tests → 73 tests OK ×2 连跑； python -m arbiter.policy capabilities.yaml → POLICY-OK default-deny=verified。 Co-authored-by: randypanding <randypanding@users.noreply.github.com>

randypanding added 2 commits August 21, 2026 23:51

fix(backend): create_commit 直接引用经典空树 SHA——POST /git/trees 空树创建被 GitHu…

c09a1b7

…b 一律 422（e2e .github#206 实测，conductor run 32493680834）(1/2)

test: GitHubRefBackend 请求形状回归测试（空树 SHA 常量/trees 零调用/parent 透传，3 例）(2/2)

50ec39e

Copilot AI lite review requested due to automatic review settings August 21, 2026 15:51

Copilot started reviewing on behalf of randypanding August 21, 2026 15:52 View session

coderabbitai Bot added the bug Something isn't working label Aug 21, 2026

Copilot AI reviewed Aug 21, 2026

View reviewed changes

Comment thread tests/test_github_backend_wire.py

Comment on lines +10 to +13

import unittest

from unittest.mock import patch

from arbiter.backend import GitHubRefBackend

qodo-code-review Bot reviewed Aug 21, 2026

View reviewed changes

randypanding merged commit 3dff55d into main Aug 21, 2026
14 checks passed

randypanding deleted the fix-empty-tree branch August 21, 2026 15:54

randypanding mentioned this pull request Aug 26, 2026

refactor: 近一周 PR 技术债清扫（行为保持） #8

Merged

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fix(backend): create_commit 直接引用经典空树 SHA（W1-C2 #165，ADR-0054） - #2

fix(backend): create_commit 直接引用经典空树 SHA（W1-C2 #165，ADR-0054）#2
randypanding merged 2 commits into
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fix-empty-tree

randypanding commented Aug 21, 2026 •

edited by coderabbitai Bot

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randypanding commented Aug 21, 2026 • edited by coderabbitai Bot Loading Uh oh! There was an error while loading. Please reload this page.

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动机

变更

验证

AC 映射（#165 AC-2/AC-5 补强）

Summary by CodeRabbit

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randypanding commented Aug 21, 2026 •

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