zebbern 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
- Multiple failures? → Yes
- Are they independent? → Yes (not related)
- Can they work in parallel? → Yes (no shared state) → Use parallel dispatch
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: Component X logic
- File B tests: Component Y behavior
- File C tests: Component Z functionality
Each domain is independent - fixing X doesn't affect Z 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
Using runSubagent tool:
runSubagent(
prompt: "Fix the failing tests in src/components/ComponentA.test.ts...",
description: "Fix ComponentA tests"
)
runSubagent(
prompt: "Fix the failing tests in src/hooks/useHookB.test.ts...",
description: "Fix useHookB tests"
)
runSubagent(
prompt: "Fix the failing tests in src/services/ServiceC.test.ts...",
description: "Fix ServiceC tests"
)
// All three run concurrently
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:
- Focused - One clear problem domain
- Self-contained - All context needed to understand the problem
- Specific about output - What should the agent return?
Fix the 3 failing tests in src/components/ImageUploader.test.tsx:
1. "should handle file upload correctly" - expects onUpload to be called
2. "should validate file type" - jpeg not accepted
3. "should show error for large files" - no error displayed
These are likely state management or event handling issues. Your task:
1. Read the test file and understand what each test verifies
2. Identify root cause - component bug or test setup issue?
3. Fix by:
- Fixing component bugs if found
- Adjusting test expectations if testing changed behavior
- Use systematic-debugging skill
Do NOT just add 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 ImageUploader.test.tsx" - 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)
Key Benefits
- Parallelization - Multiple investigations happen simultaneously
- Focus - Each agent has narrow scope, less context to track
- Independence - Agents don't interfere with each other
- Speed - 3 problems solved in time of 1
Verification
After agents return:
- Review each summary - Understand what changed
- Check for conflicts - Did agents edit same code?
- Run full suite - Verify all fixes work together
- Spot check - Agents can make systematic errors