fix: terminate final-acceptance loop when completion gate is blocked

[Cai-Tang-www]

背景

当 completion gate 未通过时，acceptance engine 会立即返回 continue，导致后续 no-progress/max-turn/retry 收敛逻辑失效，运行可能长期空转（持续注入 continue reminder）。

变更

• 调整 internal/runtime/acceptance/engine.go：
  • 取消 completion gate 未通过时的早返回。
  • 先生成 continue 决策，再统一进入 no-progress / max-turn / retry_exhausted 收敛分支。
  • 保持 completion gate 通过时原有 verifier + hook 行为不变。
• 新增/补强回归测试：
  • internal/runtime/acceptance/engine_test.go
    • completion gate=false + no_progress_exceeded => incomplete
    • completion gate=false + max_turns_reached => incomplete
    • completion gate=false + retry_exhausted => failed
  • internal/runtime/final_acceptance_test.go
    • beforeAcceptFinal 在 completion gate=false 且 no progress 超阈值时返回 incomplete

验证

• go test ./internal/runtime/acceptance ./internal/runtime -run "TestEngineEvaluateFinal|TestBeforeAcceptFinalDecisionPaths" ✅
• go test ./... ⚠️ 当前仓库存在与本改动无关的既有失败：
  • internal/gateway/launcher（绝对路径断言）
  • internal/tui/core/app（TempDir 清理）

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[fennoai]

已完成四轮审查（代码质量、性能、安全、文档一致性）。本次变更范围内未发现需要修改的显著问题。

[fennoai]

已逐项检查该处及相关分支流转，当前实现与测试覆盖能够支撑本次修复目标，暂无可行动问题。

[codecov]

Codecov Report

❌ Patch coverage is 89.74359% with 4 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
internal/runtime/acceptance/engine.go	89.74%	2 Missing and 2 partials ⚠️

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