git:20260504.ff3e8c9 to git:20260518.cdd78c8

---

name: choosing-swarm-patterns

description: Use when coordinating multiple AI agents with Agent Relay's workflow engine and need to pick the right orchestration pattern - covers the 10 core patterns (fan-out, pipeline, hub-spoke, consensus, mesh, handoff, cascade, dag, debate, hierarchical) plus 14 specialized ones, with decision framework and accurate SDK/YAML examples.

---

### Overview

The Agent Relay SDK (`@agent-relay/sdk`) supports 24 swarm patterns via a single `swarm.pattern` field. Patterns are configured declaratively in YAML or programmatically via the `workflow()` fluent builder — there are no standalone `fanOut(...)` / `hubAndSpoke(...)` helpers. Pick the simplest pattern that solves the problem; add complexity only when the system proves it's insufficient.

### Two ways to run a pattern

#### **1. YAML (portable):**

```ts

import { runWorkflow } from '@agent-relay/sdk/workflows';

const run = await runWorkflow('workflows/feature-dev.yaml', {

vars: { task: 'Add OAuth login' },

});

```

### Quick Decision Framework

#### ```

```

Is the task independent per agent?

YES → fan-out (parallel workers, hub collects)

Does each step need the previous step's output?

YES → Is it strictly linear?

YES → pipeline

NO → dag (parallel where possible, `dependsOn` edges)

Does a coordinator need to stay alive and adapt?

YES → hub-spoke (single-level hub + workers)

hierarchical (structurally identical in current impl; use for naming/intent)

Is the task about making a decision?

YES → Do agents need to argue opposing sides?

YES → debate (adversarial, full mesh)

NO → consensus (cooperative, full mesh + coordination.consensusStrategy)

Does the right specialist emerge during processing?

YES → handoff (sequential chain, one active at a time)

Do all agents need to freely collaborate?

YES → mesh (full peer-to-peer edges)

Is cost the primary concern?

YES → cascade (chain of increasingly capable agents; each step's prompt

decides whether to pass through or redo the prior output)

```

### Pattern Reference (Core 10)

| # | Pattern | Topology (actual edges) | Best For |

| --- | ---------------- | ------------------------------------------------------------------------------------------------------------------- | --------------------------------------------------------------------------- |

| 1 | **fan-out** | Hub broadcasts to N workers; workers reply to hub only | Independent subtasks (reviews, research, tests) |

| 2 | **pipeline** | Linear chain (agent*i → agent*{i+1}) | Ordered stages (design → implement → test) |

| 3 | **hub-spoke** | Hub ↔ spokes (bidirectional); no spoke-to-spoke | Dynamic coordination, lead reviews/adjusts |

| 4 | **consensus** | Full mesh; decision via `coordination.consensusStrategy` | Architecture decisions, approval gates |

| 5 | **mesh** | Full mesh (every agent ↔ every other) | Brainstorming, collaborative debugging |

| 6 | **handoff** | Chain; passes control forward | Triage, specialist routing |

| 7 | **cascade** | Chain of `dependsOn` steps; all run on success, downstream skipped on upstream failure (no built-in "fall through") | Cost optimization: cheap first, each step's prompt passes through or redoes |

| 8 | **dag** | Edges from step `dependsOn` | Mixed dependencies, parallel where possible |

| 9 | **debate** | Full mesh (same topology as mesh; roles drive behavior) | Rigorous adversarial examination |

| 10 | **hierarchical** | Hub + subordinates (single-level in current impl) | Large teams; semantic distinction from hub-spoke |

> **Heads up:** `hierarchical` resolves to the same edge structure as `hub-spoke` in `coordinator.ts:313-319`. Multi-level tree topology is not currently implemented — use pattern name for intent, but expect the same runtime graph.

### Additional Patterns (role-driven)

These 14 additional patterns exist in `SwarmPattern` (types.ts:114-139). The coordinator has role-based auto-selection heuristics (`coordinator.ts:51-165`), but they only fire when `swarm.pattern` is **omitted** — YAML validation requires it (`runner.ts:2105-2117`), so auto-selection is effectively a programmatic-API feature. In YAML, set `swarm.pattern` explicitly.

Topology is still resolved per-pattern once selected; the "Triggering roles" column reflects what the coordinator looks for to shape edges (per `coordinator.ts:250-450`):

| Pattern | Roles the topology keys off | Topology |

| ----------------- | ------------------------------------------------------- | ---------------------------------------------- |

| `map-reduce` | `mapper` + `reducer` | coordinator → mappers → reducers → coordinator |

| `scatter-gather` | — | hub → workers → hub |

| `supervisor` | `supervisor` | supervisor ↔ workers |

| `reflection` | `critic` or `reviewer` (auto-select uses `critic` only) | producers → critic → producers (loop) |

| `red-team` | `attacker`/`red-team` + `defender`/`blue-team` | adversarial mesh with optional judges |

| `verifier` | `verifier` | producers → verifiers → back to producers |

| `auction` | `auctioneer` | auctioneer → bidders → auctioneer |

| `escalation` | `tier-*` | tiered chain, escalate up / report down |

| `saga` | `saga-orchestrator`, `compensate-handler` | orchestrator ↔ participants |

| `circuit-breaker` | `primary` + `fallback`/`backup` | try primary, fallback on failure |

| `blackboard` | `blackboard` / `shared-workspace` | shared state hub |

| `swarm` | `hive-mind` / `swarm-agent` | stigmergy-style |

| `competitive` | — (declared explicitly) | independent parallel implementations + judge |

| `review-loop` | `implement*` + 2+ `reviewer*` | implementer ↔ reviewers |

### Pattern Details

#### 1. fan-out — Parallel Workers

```ts

await workflow('review')

.pattern('fan-out')

.agent('lead', { cli: 'claude', role: 'lead' })

.agent('auth-rev', { cli: 'claude', role: 'worker', interactive: false })

.agent('db-rev', { cli: 'claude', role: 'worker', interactive: false })

.step('review-auth', { agent: 'auth-rev', task: 'Review auth.ts' })

.step('review-db', { agent: 'db-rev', task: 'Review db.ts' })

.run();

```

#### 2. pipeline — Sequential Stages

```yaml

swarm: { pattern: pipeline }

agents:

- { name: designer, cli: claude }

- { name: implementer, cli: codex, interactive: false }

- { name: tester, cli: codex, interactive: false }

workflows:

- name: build

steps:

- {

name: design,

agent: designer,

task: 'Design the API schema',

verification: { type: output_contains, value: DONE },

}

- {

name: implement,

agent: implementer,

dependsOn: [design],

task: 'Implement: {{steps.design.output}}',

}

- { name: test, agent: tester, dependsOn: [implement], task: 'Write integration tests' }

```

#### 3. hub-spoke — Persistent Coordinator

```ts

await workflow('api-build')

.pattern('hub-spoke')

.channel('swarm-api')

.agent('lead', { cli: 'claude', role: 'lead' })

.agent('db-worker', { cli: 'claude', role: 'worker' }) // interactive by default — hub DMs it

.agent('api-worker', { cli: 'claude', role: 'worker' }) // interactive by default — hub DMs it

.step('models', { agent: 'db-worker', task: 'Build database models' })

.step('routes', { agent: 'api-worker', task: 'Build route handlers', dependsOn: ['models'] })

.step('review', { agent: 'lead', task: 'Review everything', dependsOn: ['routes'] })

.run();

```

#### 4. consensus — Cooperative Voting

```yaml

swarm: { pattern: consensus }

agents:

- { name: perf, cli: claude, role: reviewer }

- { name: dx, cli: claude, role: reviewer }

- { name: sec, cli: claude, role: reviewer }

coordination:

consensusStrategy: majority # declarative marker: majority | unanimous | quorum

votingThreshold: 0.66

workflows:

- name: decide

steps:

- { name: evaluate-perf, agent: perf, task: 'Evaluate perf of Fastify migration' }

- { name: evaluate-dx, agent: dx, task: 'Evaluate DX of Fastify migration' }

- { name: evaluate-sec, agent: sec, task: 'Evaluate security of Fastify migration' }

```

#### 5. mesh — Peer Collaboration

```ts

await workflow('debug-auth')

.pattern('mesh')

.channel('swarm-debug')

.agent('logs', { cli: 'claude' })

.agent('code', { cli: 'claude' })

.agent('repro', { cli: 'claude' })

.step('logs', { agent: 'logs', task: 'Check server logs' })

.step('code', { agent: 'code', task: 'Review auth code' })

.step('repro', { agent: 'repro', task: 'Write repro test' })

.run();

```

#### 6. handoff — Dynamic Routing

```yaml

swarm: { pattern: handoff }

agents:

- { name: triage, cli: claude }

- { name: billing, cli: claude }

- { name: tech, cli: claude }

workflows:

- name: support

steps:

- { name: triage, agent: triage, task: 'Triage: {{request}}' }

- { name: billing, agent: billing, dependsOn: [triage], task: 'Handle billing' }

- { name: tech, agent: tech, dependsOn: [triage], task: 'Handle tech issues' }

```

#### 7. cascade — Cost-Aware Fallthrough

```ts

await workflow('answer')

.pattern('cascade')

.agent('haiku', { cli: 'claude', model: 'claude-haiku-4-5-20251001' })

.agent('sonnet', { cli: 'claude', model: 'claude-sonnet-4-6' })

.agent('opus', { cli: 'claude', model: 'claude-opus-4-7' })

.step('try-haiku', { agent: 'haiku', task: '{{question}}' })

.step('try-sonnet', {

agent: 'sonnet',

task: 'If this is a complete answer, echo it verbatim. Otherwise answer anew:\n{{steps.try-haiku.output}}',

dependsOn: ['try-haiku'],

})

.step('try-opus', {

agent: 'opus',

task: 'Final-tier answer, using prior attempts for context:\n{{steps.try-sonnet.output}}',

dependsOn: ['try-sonnet'],

})

.run();

```

#### 8. dag — Directed Acyclic Graph

```ts

await workflow('fullstack')

.pattern('dag')

.maxConcurrency(3)

.agent('dev', { cli: 'codex', role: 'worker' })

.step('scaffold', { agent: 'dev', task: 'Create project scaffold' })

.step('frontend', { agent: 'dev', task: 'Build React UI', dependsOn: ['scaffold'] })

.step('backend', { agent: 'dev', task: 'Build API', dependsOn: ['scaffold'] })

.step('integrate', { agent: 'dev', task: 'Wire together', dependsOn: ['frontend', 'backend'] })

.run();

```

#### 9. debate — Adversarial Refinement

```yaml

swarm: { pattern: debate }

agents:

- { name: pro, cli: claude, role: debater, task: 'Argue FOR monorepo' }

- { name: con, cli: claude, role: debater, task: 'Argue FOR polyrepo' }

- { name: judge, cli: claude, role: judge, task: 'Decide after 3 rounds' }

coordination:

barriers:

- { name: debate-done, waitFor: [pro-round-3, con-round-3] }

```

#### 10. hierarchical — Multi-Level (structurally hub-spoke today)

```ts

await workflow('large-team')

.pattern('hierarchical')

.agent('lead', { cli: 'claude', role: 'lead' })

.agent('fe-coord', { cli: 'claude', role: 'coordinator' })

.agent('be-coord', { cli: 'claude', role: 'coordinator' })

.agent('fe-dev', { cli: 'codex', role: 'worker', interactive: false })

.agent('be-dev', { cli: 'codex', role: 'worker', interactive: false })

.step('plan', { agent: 'lead', task: 'Coordinate full-stack app' })

.step('fe-plan', { agent: 'fe-coord', task: 'Manage frontend', dependsOn: ['plan'] })

.step('be-plan', { agent: 'be-coord', task: 'Manage backend', dependsOn: ['plan'] })

.step('fe-impl', { agent: 'fe-dev', task: 'Build components', dependsOn: ['fe-plan'] })

.step('be-impl', { agent: 'be-dev', task: 'Build API', dependsOn: ['be-plan'] })

.run();

```

### Verification & Completion Signals

#### An agent step can complete in several ways (`runner.ts:5353-5395`, `runner.ts:4527-4538`):

```yaml

verification:

type: output_contains # or: exit_code | file_exists | custom

value: DONE # or: PLAN_COMPLETE, IMPLEMENTATION_COMPLETE, REVIEW_COMPLETE

```

### Relaycast MCP — Correct Tool Names

The skill previously referenced `mcp__relaycast__send` / `mcp__relaycast__dm` — those names are wrong. The real tools (the first three are cited in the workflow convention-injection at `relay-adapter.ts:31-35`; the rest are exposed by the live `relaycast` MCP server):

| Purpose | Tool | Source |

| ------------------------ | ------------------------------------- | --------------------- |

| Send DM to another agent | `mcp__relaycast__message_dm_send` | `relay-adapter.ts:31` |

| Check inbox | `mcp__relaycast__message_inbox_check` | `relay-adapter.ts:35` |

| List agents | `mcp__relaycast__agent_list` | `relay-adapter.ts:35` |

| Post to a channel | `mcp__relaycast__message_post` | relaycast MCP server |

| Reply in a thread | `mcp__relaycast__message_reply` | relaycast MCP server |

| Spawn sub-agent | `mcp__relaycast__agent_add` | relaycast MCP server |

| Remove sub-agent | `mcp__relaycast__agent_remove` | relaycast MCP server |

> `interactive: false` agents run as non-interactive subprocesses with no relay connection — they must NOT call any `mcp__relaycast__*` tool (validator warns on this at `validator.ts:138-150`, check `NONINTERACTIVE_RELAY`).

### Reflection (Trajectories)

#### Reflection is **not** a `reflectionThreshold` callback. It's configured via the `trajectories:` block:

```yaml

trajectories:

enabled: true

reflectOnBarriers: true # config flag exists but runner does NOT currently invoke this path

reflectOnConverge: true # fires at parallel convergence points (runner.ts:2762-2779)

autoDecisions: true # record retry/skip/fail decisions

```

### Common Mistakes

| Mistake | Why It Fails | Fix |

| -------------------------------------------- | ----------------------------------------------------------------------------- | --------------------------------------------------------------------------------------------- |

| Using mesh/debate for everything | Full-mesh blows up message volume past ~5 agents | Use hub-spoke or dag for most tasks |

| Pipeline for independent work | Sequential bottleneck | Use fan-out or dag |

| Hub-spoke for 2 agents | Hub is unnecessary overhead | Use pipeline or fan-out |

| Expecting `consensusStrategy` to tally votes | Runner has no vote-tally logic; field only affects coordinator auto-selection | Aggregate votes in a judge/lead step that reads `{{steps.*.output}}` |

| Handoff with "routing = skip other branches" | Skipping only fires on upstream **failure**, not routing decisions | Emit a routing token in triage output; downstream prompts self-no-op if token doesn't match |

| Cascade expecting skip-on-success | Runner has no cascade skip logic; failed upstream skips downstream | Chain downstream prompts to pass-through or redo based on `{{steps.previous.output}}` |

| Relying on `reflectOnBarriers` | Config flag exists but runner never calls it | Use `reflectOnConverge` for convergence reflection; use `reflection` pattern for critic loops |

| `interactive: false` agent calling MCP | Non-interactive subprocess has no relay | Use `interactive: true` (default) or emit output on stdout |

| Relying on multi-level `hierarchical` | Topology is single-level hub in current impl | Use pattern for naming; model levels via `dependsOn` graph |

| Writing `mcp__relaycast__send(...)` | Wrong tool name | Use `mcp__relaycast__message_post` or `message_dm_send` |

### Resume & Re-run

#### ```ts

```ts

// Resume a failed run:

await runWorkflow('feature-dev.yaml', { resume: '<runId>' });

// Skip ahead, re-using cached outputs from an earlier run:

await runWorkflow('feature-dev.yaml', {

startFrom: 'review',

previousRunId: '<runId>',

});

```

### Complete YAML Example

#### ```yaml

```yaml

version: '1.0'

name: feature-dev

description: 'Blueprint-style feature development with quality gates.'

swarm:

pattern: hub-spoke

maxConcurrency: 2

timeoutMs: 3600000

channel: swarm-feature-dev

idleNudge: { nudgeAfterMs: 120000, escalateAfterMs: 120000, maxNudges: 1 }

agents:

- { name: lead, cli: claude, role: lead, permissions: { access: full } }

- { name: planner, cli: codex, role: planner, interactive: false, permissions: { access: readonly } }

- { name: developer, cli: codex, role: worker, interactive: false, permissions: { access: readwrite } }

- { name: reviewer, cli: claude, role: reviewer, permissions: { access: readonly } }

workflows:

- name: feature-delivery

onError: retry

preflight:

- { command: 'git status --porcelain', failIf: non-empty, description: 'Clean worktree' }

steps:

- name: plan

agent: planner

task: 'Plan: {{task}}'

verification: { type: output_contains, value: PLAN_COMPLETE }

- name: implement

agent: developer

dependsOn: [plan]

task: 'Implement: {{steps.plan.output}}'

verification: { type: output_contains, value: IMPLEMENTATION_COMPLETE }

- name: test

type: deterministic

dependsOn: [implement]

command: npm test

- name: review

agent: reviewer

dependsOn: [test]

task: 'Review implementation'

verification: { type: output_contains, value: REVIEW_COMPLETE }

coordination:

barriers:

- { name: delivery-ready, waitFor: [plan, implement, review], timeoutMs: 900000 }

trajectories:

enabled: true

reflectOnBarriers: true

reflectOnConverge: true

errorHandling:

strategy: retry

maxRetries: 2

retryDelayMs: 5000

```

### Source of Truth

| Claim | File |

| ----------------------------------------------------------------- | ---------------------------------------------------------------------------- |

| Pattern enum (24 patterns) | `packages/sdk/src/workflows/types.ts:114-139` |

| Topology resolution per pattern | `packages/sdk/src/workflows/coordinator.ts:240-450` |

| Interactive-only topology edges | `packages/sdk/src/workflows/coordinator.ts:218-237` |

| Pattern auto-selection heuristics (programmatic API only) | `packages/sdk/src/workflows/coordinator.ts:51-165` |

| `WorkflowBuilder` fluent API | `packages/sdk/src/workflows/builder.ts` |

| `runWorkflow(yamlPath, options)` | `packages/sdk/src/workflows/run.ts` |

| YAML validation requires `version` + `name` + `swarm.pattern` | `packages/sdk/src/workflows/runner.ts:2105-2117` |

| MCP tool names cited in convention-injection | `packages/sdk/src/relay-adapter.ts:29-36` |

| Completion modes (verification / evidence / owner / process-exit) | `packages/sdk/src/workflows/runner.ts:5353-5395`, `4527-4538` |

| Completion via PTY + summary fallback | `packages/sdk/src/workflows/runner.ts:6600-6615` |

| Downstream skip on upstream failure (not success) | `packages/sdk/src/workflows/runner.ts:7057-7088`, `step-executor.ts:329-334` |

| Trajectory reflection (only `reflectOnConverge` wired) | `packages/sdk/src/workflows/runner.ts:2762-2779`, `trajectory.ts:173-190` |