Dispatching Parallel Agents

Dispatching Parallel Agents

Overview

When you have multiple unrelated failures (different test files, different subsystems, different bugs), investigating them sequentially wastes time. Each investigation is independent and can happen in parallel.

Core principle: Dispatch one agent per independent problem domain. Let them work concurrently.

When to Use

digraph when_to_use {
    "Multiple failures?" [shape=diamond];
    "Are they independent?" [shape=diamond];
    "Single agent investigates all" [shape=box];
    "One agent per problem domain" [shape=box];
    "Can they work in parallel?" [shape=diamond];
    "Sequential agents" [shape=box];
    "Parallel dispatch" [shape=box];

    "Multiple failures?" -> "Are they independent?" [label="yes"];
    "Are they independent?" -> "Single agent investigates all" [label="no - related"];
    "Are they independent?" -> "Can they work in parallel?" [label="yes"];
    "Can they work in parallel?" -> "Parallel dispatch" [label="yes"];
    "Can they work in parallel?" -> "Sequential agents" [label="no - shared state"];
}

Use when: 3+ failures with different root causes, multiple independent subsystems broken, no shared state between investigations.

Don't use when: failures are related, need full system context, agents would interfere (editing same files).

The Pattern

1. Identify Independent Domains

Group failures by what's broken. Each domain is independent — fixing one doesn't affect others.

2. Create Focused Agent Tasks

Each agent gets: specific scope (one file/subsystem), clear goal, constraints (don't change other code), expected output (summary of findings and fixes). Include a return format constraint: token budget (e.g., "under 1000 tokens") and structure (e.g., "verdict first, then details").

Model selection: Use Opus for implementation agents, Sonnet for review/analysis agents, Haiku for simple validation or formatting tasks.

Use the dispatch prompt template for the canonical 6-section prompt structure.

3. Dispatch in Parallel

Task("Fix agent-tool-abort.test.ts failures")
Task("Fix batch-completion-behavior.test.ts failures")
Task("Fix tool-approval-race-conditions.test.ts failures")

4. Review and Integrate

Read each summary, verify fixes don't conflict, run full test suite, integrate all changes.

When NOT to Use

• Related failures: Fix one might fix others — investigate together first
• Need full context: Understanding requires seeing entire system
• Exploratory debugging: You don't know what's broken yet
• Shared state: Agents would interfere (consider git worktrees for isolation if parallelism is otherwise beneficial)

Verification

After agents return:

1. Review each summary — Understand what changed
2. Check for conflicts — Did agents edit same code?
3. Run full suite — Verify all fixes work together
4. Spot check — Agents can make systematic errors

For agent prompt structure, common mistakes, and a real example walkthrough, see references/agent-prompts-and-examples.md.