Record U3 r0.4 design for review

Why: preserve the failed A01 outcome and an actionable design for reliable staged material work.

Evidence: Documents links and diff checks pass; Dev make test passed with the staged Documents gitlink; original A01 and offline diagnostic receipts remain SELF.

Impact: documentation, task-card evidence and Documents pin only; no product behavior or model budget change.

Refs: modules/documents/docs/proposals/2026-10-14-fast-slow-u3-r04-reliable-first-checkpoint-design.md; .task/feature-fast-slow-u2-u3-plan.md

PROJECT.md

@@ -70,5 +70,5 @@ U2 起实施与部署分别评审。
 
 - [渐进工作台界面重设计 r0.2](modules/documents/docs/proposals/2026-10-12-work-companion-ui-design.md)：用户已授权连续实施；[计划 r1](modules/documents/docs/proposals/2026-10-12-work-companion-ui-plan.md)覆盖任务摘要、对话/输入、窄屏和真实状态投影；进展见对应任务卡。
 
-- [快慢通道 U2/U3 实施计划 r0.1](modules/documents/docs/proposals/2026-10-13-fast-slow-u2-u3-plan.md)：r0.2 唯一获批 A01 已执行，因无依据的分期归属判断，真实模型质量仍 FAIL，尚未合入或部署。[有依据的阶段判断设计 r0.3](modules/documents/docs/proposals/2026-10-13-fast-slow-u3-r03-evidence-backed-judgments-design.md)与[详细实施计划](modules/documents/docs/proposals/2026-10-13-fast-slow-u3-r03-evidence-implementation-plan.md)已获用户批准；零付费实现、机制验证和独立代码复审完成，待阶段6人工审阅与单独付费样本资源批准。详见[核验报告](modules/documents/docs/reports/2026-10-13-fast-slow-u2-u3-validation.md)。
+- [快慢通道 U2/U3 实施计划 r0.1](modules/documents/docs/proposals/2026-10-13-fast-slow-u2-u3-plan.md)：r0.2 因无依据的分期归属、r0.3 因首个检查点参数不完整且零阶段成果，真实模型质量均为 FAIL；六 PR 保持草稿，未合入或部署。[r0.3 设计](modules/documents/docs/proposals/2026-10-13-fast-slow-u3-r03-evidence-backed-judgments-design.md)及[实施计划](modules/documents/docs/proposals/2026-10-13-fast-slow-u3-r03-evidence-implementation-plan.md)已获批准并形成零付费候选；[r0.4 首条阶段发现与失败收口设计](modules/documents/docs/proposals/2026-10-14-fast-slow-u3-r04-reliable-first-checkpoint-design.md)仅获方向批准，书面版本待评审，不授权代码或新付费样本。详见[核验报告](modules/documents/docs/reports/2026-10-13-fast-slow-u2-u3-validation.md)。
 - [系统项目、成员工作入口与私域协作闭环 r1](modules/documents/docs/proposals/2026-10-13-system-project-membership.md)：2026-10-13 用户批准阶段 1–9 连续推进；统一全局项目身份与名称、成员个人会话、每项目两树一网和私域权限；当前组合验证/CI/tag 消费推进中，部署与线上修复未授权。