bjornmelin/fan-out

Fan-out

Bounded subagent delegation and evidence-first synthesis for Claude Code. You stay the planner and the single decision-maker; subagents do scoped work and hand back evidence you merge.

When to fan out (and when not to)

Spawn only if at least one is true:

• The user explicitly asked to delegate / parallelize / spawn subagents.
• The task splits into 2-5 genuinely independent subtasks (no shared mutable state).
• Independent work would otherwise pollute the main context (large reads, broad searches).

Otherwise keep it local. Do not rationalize a spawn for work that is sequential, tiny, or shares write surface — coordination overhead and edit collisions cost more than they save.

Mechanism selection

| Situation | Use | |---|---| | One bounded subtask, keep main context clean | a single Task call | | 2-5 independent subtasks, need all results together | batch Task calls in one message (they run concurrently) | | Dependent / multi-stage / DAG-shaped batch | the dynamic Workflow tool (pipeline/parallel/agent stages) | | Genuinely long-running, parent must stay responsive | background Bash task (run_in_background) + TaskGet/TaskStop |

Default to batched Task calls. Reach for Workflow only when stages depend on each other or you need loop/fan-out control flow; reach for background tasks only for true async.

Spawn contract (every subagent prompt)

TASK:    <one concrete outcome>
SCOPE:   <paths / area to look at; what is out of bounds>
MODE:    read-only  |  edit ONLY <named files>
CONTEXT: <self-contained — subagents inherit NO parent transcript>
RETURN:  <exact shape: status, evidence (file:line), commands run, findings + confidence, risks>

Subagents start fresh with no conversation history — never reference "the above" or prior turns.

Roles & model policy

• Pick a custom .claude/agents/<role>.md when one matches; else general-purpose.
• Opus for hard reasoning, review, debugging, planning; inherit (or Sonnet) for read-heavy scans and inventories. Pin model: in the agent file, or omit to inherit the session model.
• Default subagents to read-only (no Edit/Write in their tool scope) unless they own a disjoint, named write surface.

Rendezvous & async discipline

• Synchronous Task batches block until every subagent returns — read all results before the next substantive step; never act on a partial mental model.
• Background tasks: account for every one via TaskGet; TaskStop anything stale or superseded.

Limits & edit safety

• Prefer 2-5 agents; more dilutes synthesis. No nested subagents unless the user asks.
• Parallel edit-workers must own disjoint files. Tell each: "you are not alone in this repo — do not revert or restage another worker's changes." The parent serializes commits.

Escalation

If a subagent underfits, tighten its scope and return contract and re-run only that one on a stronger (Opus) role. Never blanket-escalate the whole batch.

Synthesis & conflict ledger

Merge and dedupe returns; lead with the highest-signal evidence. When subagents disagree, record it and resolve in the parent:

CONFLICT: <claim>
  - agent A: <evidence>
  - agent B: <evidence>
  RESOLUTION: <which wins + why, or the remaining uncertainty>

Verification

Any proposed edit ships with tests/checks actually run, or a concrete command-level verification plan the parent (or a final verify subagent) executes.

Failure modes

| Symptom | Fix | |---|---| | Subagent overscoped / wandered | tighter SCOPE + RETURN contract | | Weak / unusable output | specify exact return shape + evidence format | | Parent acted on partial results | wait for all returns before deciding | | Forgot a background task | reconcile every task via TaskGet | | Edit collision | disjoint write surfaces; parent serializes commits | | Role underfit | re-run only that agent on Opus | | Too many agents | collapse to 2-5 with broader scopes |

See references/agent-templates.md for copyable role stubs and a Workflow skeleton.