feat(generation): 立绘 sheet 源格按 PerfectPixel 口径做朝向 QC

[xiaocheny214]

Summary

• 四向/八向立绘 sheet 没有改 HTTP：请求体、计费冻额（2/4）、result.sheets[] 形状不变。这是执行器生产管线。
• 源格在抠图后、吸附/对齐前检查空图、非背面身份、east 正面漂；失败把英文 RetryHints 喂进下一轮，每格最多 3 次，三次仍失败 keep-best。
• 提示词身份节加上 facing lock；定妆像素项目拼同一套 grid 约束。冻额不乘 3。

Refs #779
Close #779

Test plan

• cd backend && uv run pytest tests/test_view_sheet_executor.py tests/test_view_sheet_prompt.py tests/test_identity_histogram.py tests/test_view_sheet_orchestration.py tests/test_master_cutout.py -q
• 四向仍冻 2 次、八向仍冻 4 次；格内 QC 重试不另加价
• 不透明测试母版不触发身份/朝向重试（仍是 2/4 次模型调用）
• 透明底 east 画得和 south 一样宽时，第二轮提示词带 QUALITY CORRECTIONS / never-drift
• 三次仍失败任务仍 completed，不整单失败
• POST /generation/four-view / eight-view 请求与响应字段与 feat(generation): 四向/八向立绘 sheet 调用约定（正视定妆 → 确认母版 → four-view/eight-view） #755 一致

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1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
windup	Ignored	Preview	Aug 26, 2026 1:15pm

[github-actions]

✅ 此 PR 已关联 issue，之前的提醒已自动标记为已解决。

[codecov]

Codecov Report

❌ Patch coverage is 93.44262% with 12 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...dup_app/server/orchestrator/view_sheet_executor.py	88.60%	9 Missing ⚠️
...ai_engine/src/windup_ai_engine/slicing/identity.py	96.59%	3 Missing ⚠️

@@            Coverage Diff             @@
##             main     #781      +/-   ##
==========================================
+ Coverage   87.74%   87.82%   +0.07%     
==========================================
  Files         280      281       +1     
  Lines       20502    20683     +181     
  Branches     3051     3053       +2     
==========================================
+ Hits        17990    18165     +175     
- Misses       1672     1679       +7     
+ Partials      840      839       -1     

Flag	Coverage Δ
backend	92.01% <93.44%> (+0.05%)	⬆️
frontend	82.64% <ø> (+0.04%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
.../ai_engine/src/windup_ai_engine/prompt/__init__.py	100.00% <100.00%> (ø)
...i_engine/src/windup_ai_engine/prompt/view_sheet.py	100.00% <100.00%> (ø)
...app/src/windup_app/server/orchestrator/executor.py	78.64% <100.00%> (+0.29%)	⬆️
...ai_engine/src/windup_ai_engine/slicing/identity.py	96.59% <96.59%> (ø)
...dup_app/server/orchestrator/view_sheet_executor.py	87.81% <88.60%> (-0.29%)	⬇️

... and 3 files with indirect coverage changes

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[fennoai]

Reviewed the complete fixed-range diff across the identity/QC primitives, prompt construction, and sheet orchestration contracts. The QC retry behavior, mirror assembly, and prompt feedback composition are coherent. One worker-startup integration regression is blocking: the executor export removed below is still imported by bootstrap.worker, so the production worker cannot import and start. Static validation completed with py_compile; the repository test command could not run because uv is unavailable in the environment.