chore: import upstream snapshot with attribution

cli-tool/components/loops/engineering/build-test-fix-loop.md

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+---
+name: build-test-fix-loop
+description: Builds the next item on the plan, then runs tests, typecheck and lint, feeding every failure back as the next instruction until the build is green.
+category: engineering
+interval: 10m
+stop-condition: The build is green — tests, typecheck and lint all pass — and the checker reports nothing left to fix.
+components: [agent:development-team/test-runner, hook:testing/test-runner, command:testing/generate-tests]
+tags: [testing, build, ci, loop]
+---
+
+# Build–Test–Fix Loop
+
+> **Loop Engineering** — the single most-demoed loop pattern: a builder writes code and a checker runs tests, typecheck and lint and reports exactly what broke. They pass work back and forth until it's clean. A one-shot agent ships its bugs; this loop catches them.
+
+## 🎯 Goal
+Implement the next item on the plan, then run the full check gate (tests + typecheck + lint), feed **every** failure back as the next instruction, and repeat until the build is green.
+
+## ⏱️ Schedule
+Suggested interval: `10m` (or run until done on a feature).
+
+## ▶️ Run it
+```
+/loop 10m "Build the next item on the plan, then run tests, typecheck and lint. Feed every failure back as the next instruction and fix it. Add a test for anything that lacked coverage. Stop when the build is green and the checker has nothing left to report."
+```
+
+## 🔁 Iteration steps
+1. **Build** — implement the next plan item.
+2. **Check** — the `test-runner` hook runs tests, typecheck and lint automatically.
+3. **Reason** — collect every failure into a concrete fix list.
+4. **Act** — fix each; add tests with `/generate-tests` for uncovered paths.
+5. **Observe** — re-run the gate; loop until fully green.
+
+## 🛑 Stopping condition
+Tests, typecheck and lint all pass and the checker reports nothing outstanding.
+
+## 💰 Budget & guardrails
+Cap iterations or spend so a stubborn failure can't spin forever — surface anything that fails the same way twice for human eyes.
+
+## 🧩 Referenced components
+- `agent:development-team/test-runner` — runs and interprets the check gate.
+- `hook:testing/test-runner` — fires the suite automatically each pass.
+- `command:testing/generate-tests` — covers gaps the loop uncovers.
+
+## 💡 Example
+Implementing a new endpoint, the loop catches a type error, then a failing integration test, then a lint warning — fixing each in turn — and exits only when all three gates are green.