Agent SwarmPattern: Drain Loops (Stacked PRs + Merge Loop)
Turn one big parent issue into a chain of small, individually-reviewable stacked PRs, then review-and-merge them bottom-up with a merge loop that halts on the first failure.
Turn one big parent issue into a chain of small, individually-reviewable PRs — then review-and-merge them bottom-up, halting on the first failure.
What it is
Two complementary loops:
- Drain loop — iterate the sub-issues of a parent. For each: branch off the previous PR's branch (so PRs stack), implement, push, open a PR, move the sub-issue to In Review. Repeat until drained.
- Merge loop — review the bottom-most open PR with
base=main. If the reviewer approves and CI is green, squash-merge it, move the sub-issue to Done, and loop up the stack. Halt on the first request-changes or red CI so a bad change doesn't cascade.
Where we use it
- Feature development —
linear-drain-loop+linear-merge-loopdrive a Linear epic from sub-issues to merged PRs. - Weekly code-health — top-N concerns become one PR each, drained with an internal reviewer (capped review rounds).
- UX audits — an umbrella's sub-issues can feed a drain loop for the low-risk fixes.
Why it works
- Small PRs review faster and roll back cleaner than one mega-PR.
- Stacking keeps the chain coherent while each piece stays independently reviewable.
- Halting on first failure prevents a broken base from poisoning everything above it.
How to apply
- Each sub-issue must be independently mergeable — if they're entangled, the stack breaks.
- Cap iterations (
maxIterations) so a runaway loop can't churn forever. - Keep tracker state in lockstep: In Review on PR open, Done on merge. Stale tracker state is the usual failure mode.
Used in
Pattern: Litmus Tests (LLM-as-Judge Quality Gates)
A quality gate where one agent hard-rejects another agent's output against an explicit rubric — using a different model family so the judgment is genuinely independent and not rubber-stamping in disguise.
Pattern: HITL Gates (Human-in-the-Loop Approval)
Pause a workflow mid-flight until a human approves in Slack. The agent does the work; the human owns the irreversible decision (sending, merging, deleting, posting publicly).