dispatching-parallel-agents

What this skill does

# 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

```dot
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+ test files failing with different root causes
- Multiple subsystems broken independently
- Each problem can be understood without context from others
- No shared state between investigations

**Don't use when:**
- Failures are related (fix one might fix others)
- Need to understand full system state
- Agents would interfere with each other

## The Pattern

### 1. Identify Independent Domains

Group failures by what's broken:
- File A tests: Tool approval flow
- File B tests: Batch completion behavior
- File C tests: Abort functionality

Each domain is independent - fixing tool approval doesn't affect abort tests.

### 2. Create Focused Agent Tasks

Each agent gets:
- **Specific scope:** One test file or subsystem
- **Clear goal:** Make these tests pass
- **Constraints:** Don't change other code
- **Expected output:** Summary of what you found and fixed

### 3. Dispatch in Parallel

**CRITICAL:** All Task calls must be in a **single message** to run in parallel.

```
// Use the Task tool with these parameters:

Task 1:
  description: "Fix abort test failures"
  prompt: "Fix the 3 failing tests in agent-tool-abort.test.ts..."
  subagent_type: "general-purpose"

Task 2:
  description: "Fix batch completion failures"
  prompt: "Fix the 2 failing tests in batch-completion-behavior.test.ts..."
  subagent_type: "general-purpose"

Task 3:
  description: "Fix race condition failures"
  prompt: "Fix the failing test in tool-approval-race-conditions.test.ts..."
  subagent_type: "general-purpose"

// All three in ONE message = parallel execution
```

**Available subagent_type options:**
- `general-purpose` - For most tasks (searching, coding, multi-step work)
- `Bash` - For command execution tasks
- `Explore` - For codebase exploration (specify thoroughness: "quick", "medium", "very thorough")
- `Plan` - For designing implementation plans
- Custom agents from `agents/` directory (e.g., your defined agents)

**Using Explore for parallel codebase analysis:**
```
Task 1:
  description: "Find auth implementation"
  prompt: "Find how authentication is implemented. Thoroughness: medium"
  subagent_type: "Explore"

Task 2:
  description: "Find API endpoints"
  prompt: "Find all API endpoint definitions. Thoroughness: quick"
  subagent_type: "Explore"

Task 3:
  description: "Find database models"
  prompt: "Find all database model definitions. Thoroughness: medium"
  subagent_type: "Explore"
```

### 4. Review and Integrate

When agents return:
- Read each summary
- Verify fixes don't conflict
- Run full test suite
- Integrate all changes

## Agent Prompt Structure

Good agent prompts are:
1. **Focused** - One clear problem domain
2. **Self-contained** - All context needed to understand the problem
3. **Specific about output** - What should the agent return?

```markdown
Fix the 3 failing tests in src/agents/agent-tool-abort.test.ts:

1. "should abort tool with partial output capture" - expects 'interrupted at' in message
2. "should handle mixed completed and aborted tools" - fast tool aborted instead of completed
3. "should properly track pendingToolCount" - expects 3 results but gets 0

These are timing/race condition issues. Your task:

1. Read the test file and understand what each test verifies
2. Identify root cause - timing issues or actual bugs?
3. Fix by:
   - Replacing arbitrary timeouts with event-based waiting
   - Fixing bugs in abort implementation if found
   - Adjusting test expectations if testing changed behavior

Do NOT just increase timeouts - find the real issue.

Return: Summary of what you found and what you fixed.
```

## Common Mistakes

**❌ Too broad:** "Fix all the tests" - agent gets lost
**✅ Specific:** "Fix agent-tool-abort.test.ts" - focused scope

**❌ No context:** "Fix the race condition" - agent doesn't know where
**✅ Context:** Paste the error messages and test names

**❌ No constraints:** Agent might refactor everything
**✅ Constraints:** "Do NOT change production code" or "Fix tests only"

**❌ Vague output:** "Fix it" - you don't know what changed
**✅ Specific:** "Return summary of root cause and changes"

## When NOT to Use

**Related failures:** Fixing 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 (editing same files, using same resources)

## Real Example from Session

**Scenario:** 6 test failures across 3 files after major refactoring

**Failures:**
- agent-tool-abort.test.ts: 3 failures (timing issues)
- batch-completion-behavior.test.ts: 2 failures (tools not executing)
- tool-approval-race-conditions.test.ts: 1 failure (execution count = 0)

**Decision:** Independent domains - abort logic separate from batch completion separate from race conditions

**Dispatch:**
```
Agent 1 → Fix agent-tool-abort.test.ts
Agent 2 → Fix batch-completion-behavior.test.ts
Agent 3 → Fix tool-approval-race-conditions.test.ts
```

**Results:**
- Agent 1: Replaced timeouts with event-based waiting
- Agent 2: Fixed event structure bug (threadId in wrong place)
- Agent 3: Added wait for async tool execution to complete

**Integration:** All fixes independent, no conflicts, full suite green

**Time saved:** 3 problems solved in parallel vs sequentially

## Key Benefits

1. **Parallelization** - Multiple investigations happen simultaneously
2. **Focus** - Each agent has narrow scope, less context to track
3. **Independence** - Agents don't interfere with each other
4. **Speed** - 3 problems solved in time of 1

## Advanced Task Tool Features

### Background Execution

Run agents in background while you continue working:

```
Task:
  description: "Run slow analysis"
  prompt: "Analyze the entire codebase for..."
  subagent_type: "general-purpose"
  run_in_background: true

// Returns immediately with output_file path
// Use Read tool or `tail` to check progress later
```

### Agent Resumption

Resume a previous agent to continue its work:

```
Task:
  description: "Continue previous analysis"
  prompt: "Continue from where you left off..."
  subagent_type: "general-purpose"
  resume: "<agent-id-from-previous-run>"

// Agent continues with full previous context preserved
```

### Model Selection

Choose appropriate model for task complexity:

```
Task:
  description: "Quick formatting check"
  prompt: "Check if files follow naming convention..."
  subagent_type: "general-purpose"
  model: "haiku"  // Fast, low-cost for simple tasks

Task:
  description: "Complex architecture analysis"
  prompt: "Design the migration strategy..."
  subagent_type: "general-purpose"
  model: "opus"  // Most capable for complex reasoning
```

### Using Custom Agents

Define agents in `agents/` directory, then use them:

```
Task:
  description: "Security review"
  prompt: "[plan content]"
  subagent_type