[nostalume]

Summary / 摘要

Fix a partitioned-download cancellation path that could return a nil reader with a nil error and then panic while serving a proxy request. Preserve the acquisition error after cleanup; start a worker only after its first chunk is queued, so a cancelled queue attempt cannot release its concurrency slot twice.

The change is independent of the now-closed #3089 and does not alter configuration, storage format, or public API. The tests cover the downloader's single-part cancellation/upstream failure, multi-part cancellation and concurrency-slot ownership, and the public proxy panic. Already-written HTTP response status is intentionally not remapped in this PR.

• This PR has breaking changes.
  / 此 PR 包含破坏性变更。
• This PR changes public API, config, storage format, or migration behavior.
  / 此 PR 修改了公开 API、配置、存储格式或迁移行为。
• This PR requires corresponding changes in related repositories.
  / 此 PR 需要关联仓库同步修改。

Related repository PRs / 关联仓库 PR:

• OpenList-Frontend: none
• OpenList-Docs: none

Testing / 测试

• go test ./... (not run)
• go test ./internal/net -run '^(TestDownload|TestHighConcurrency)' -count=1 on Windows/amd64, Go 1.27.1
• go test ./server/common -count=1 on Windows/amd64, Go 1.27.1
• go vet ./internal/net ./server/common on Windows/amd64, Go 1.27.1
• CGO_ENABLED=1 go test -race ./internal/net ./server/common -run '^(TestDownloadCancelledAcquisitionReturnsErrorAndReleasesLimit|TestDownloadSinglePartFailureReleasesLimit|TestProxyCancelledPartitionedReaderDoesNotPanic)$' -count=3 on Linux/amd64 (WSL), Go 1.27.1

Known unrelated baseline failures, reproduced on the unmodified main-based worktree: the full Windows go test ./internal/net fails TestNewOSSClientUsesEnvironmentHTTPSProxy (*net.safeTransport versus expected *http.Transport); Linux -race on existing TestHighConcurrency reports a HybridCache.BufferStore.WriteAt/GrowTo race. Neither is addressed in this PR.

Checklist / 检查清单

• I have read CONTRIBUTING.
  / 我已阅读 CONTRIBUTING。
• I confirm this contribution follows the repository license, contribution policy, and code of conduct. (Pending human collaborator confirmation.)
  / 待人工协作者确认。
• I have formatted the changed code with gofmt.
  / 已格式化变更代码。
• I have requested review from relevant maintainers or code owners where applicable.
  / 已请求相关维护者或代码所有者审查。

AI Disclosure / AI 使用声明

• This PR includes AI-assisted content.
  / 此 PR 包含 AI 辅助内容。

Tools used / 使用工具:

• Codex

Usage scope / 使用范围:

• Code generation / 代码生成

• Tests / 测试

• Review assistance / 审查辅助

• I have reviewed and validated all AI-assisted content included in this PR. (Pending human collaborator review.)

• I have ensured that all AI-assisted commits include Co-authored-by attribution.

• I can reproduce all AI-assisted content included in this PR without any AI tools. (Pending human collaborator confirmation.)

[pikachuren]

🙏 感谢 @nostalume 提交！
🤖 AI 自动审核声明：本评审报告由 AI 自动生成，当前使用 Claude Opus 5 模型进行分析。
⚠️ AI 分析结果仅供参考，可能存在误判或遗漏。如您发现任何问题或有不同意见，欢迎随时提出讨论和纠正。
⚠️ 重要提醒：即使 AI 评审认为代码质量良好且建议合并，最终是否合并仍需由项目维护者进行人工判定。项目维护者会综合考虑代码质量、项目规划、技术方向、团队资源等多方面因素做出是否合并的决策。

🎯 结论

✅ Approve — 代码质量良好，建议合并

📖 概要

fix(net): preserve cancellation errors during partitioned downloads

📊 评审结果

改动合理，无重大问题发现。代码逻辑清晰，符合项目规范。

🎯 结论：✅ Approve — 建议合并