chore: import upstream snapshot with attribution

cli-tool/components/loops/engineering/builder-reviewer-loop.md

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+---
+name: builder-reviewer-loop
+description: Passes code between a builder and an independent reviewer subagent until the review has no blocking findings and tests pass.
+category: engineering
+interval: 15m
+stop-condition: The reviewer reports zero blocking findings and the full test suite passes.
+components: [agent:expert-advisors/architect-review, agent:development-team/test-runner, command:git-workflow/pr-review]
+tags: [code-review, subagents, quality, loop]
+---
+
+# Builder–Reviewer Loop
+
+> **Loop Engineering** — separate the *builder* from the *reviewer* so the agent doesn't grade its own work. Code bounces between them until it genuinely passes.
+
+## 🎯 Goal
+Implement a change, then have an **independent reviewer subagent** critique it; iterate on the findings until the review is clean and tests are green.
+
+## ⏱️ Schedule
+Suggested interval: `15m` (or run until done on a single feature).
+
+## ▶️ Run it
+```
+/loop 15m "Implement the next slice of the feature. Then hand it to an independent reviewer subagent for an adversarial review. Address every blocking finding and re-run tests. Continue until the reviewer has no blocking findings and the suite passes."
+```
+
+## 🔁 Iteration steps
+1. **Build** — implement the next slice of work.
+2. **Review** — the `architect-review` agent inspects the diff for correctness, design and risk.
+3. **Plan** — collect blocking findings into a fix list.
+4. **Act** — address each finding; re-run the suite with `test-runner`.
+5. **Observe** — re-review with `/pr-review`; if blocking findings remain, loop again.
+
+## 🛑 Stopping condition
+Reviewer reports zero blocking findings **and** all tests pass.
+
+## 🧩 Referenced components
+- `agent:expert-advisors/architect-review` — the independent reviewer (no self-grading).
+- `agent:development-team/test-runner` — runs the suite each pass.
+- `command:git-workflow/pr-review` — structured review checklist.
+
+## 💡 Example
+The builder ships a new caching layer; the reviewer flags a race condition and a missing eviction test. The loop fixes both, re-reviews, and exits clean.