Agent Skills: Implementation Subagents

Implementation Subagents

Fresh subagent per task. One combined review per completed batch. Parallel when independent, sequential when dependent.

When to Use Subagents

Use when:

• 2+ independent work items do not share state or files
• Each work item has explicit requirements, constraints, files, and validation
• Each problem can be understood without context from the other work items

Don't use when:

• Tasks are tightly coupled (editing the same files)
• You need to understand full system state across tasks
• Failures are related (fixing one might fix others)
• Exploratory work where the problem isn't well-defined yet

Dispatch Modes

Sequential (dependent tasks)

Tasks with dependencies execute one at a time. Each gets a fresh subagent — no context pollution from previous tasks.

Task 1 (Entity) → review → complete
Task 2 (Repository, depends on T1) → review → complete
Task 3 (Service, depends on T2) → review → complete

Parallel (independent tasks)

Independent tasks dispatch simultaneously. One agent per problem domain.

Task A (auth tests) ──→ review → complete
Task B (billing tests) ──→ review → complete    ← concurrent
Task C (notification tests) ──→ review → complete

Independence check: Would fixing Task A affect Task B? Would they edit the same files? If no to both, dispatch in parallel.

For shared-tree parallel work:

1. Assign each task an exclusive file list before dispatch
2. Do not let implementers stage or commit changes
3. Capture full git status, including untracked files, before and after each task
4. Capture the task's path-scoped patch and reject changes outside its assigned paths
5. Run tasks sequentially if their file ownership overlaps or cannot be isolated

Prompt Templates

Use these templates when dispatching subagents. Each template is battle-tested — don't improvise, use them as-is and fill in the variables.

• references/implementor-prompt.md — Dispatch an implementer. Includes self-review checklist.
• references/batch-reviewer-prompt.md — Combined plan and code-quality review for one completed batch.

Prompt quality rules

• Focused — one task, one problem domain
• Self-contained — all context needed is in the prompt. Provide the complete work-item requirements; do not make the subagent recover context
• Specific about files — exact paths, not "the relevant files"
• Specific about output — what should the subagent return?
• Constrained — what should they NOT touch?

Common mistakes

| Mistake | Fix | |---------|-----| | "Fix all the tests" | "Fix the 3 failures in user.test.ts" | | No context about codebase | Paste the relevant patterns and conventions | | No constraints | "Do NOT change production code" or scope to specific files | | Vague output expectations | "Return: root cause, changes made, test results" |

Batch Review

Run one combined review after every completed batch, not separate reviews for each task.

Give one fresh reviewer:

• The complete requirements for work items in the batch
• The relevant constraints
• The path-scoped patch captured for each task
• The full changed-file inventory, including untracked files
• The implementers' reports and validation results

The reviewer checks both requirements compliance and code quality:

1. Every requirement and acceptance criterion is implemented
2. The batch follows the supplied constraints
3. No unrequested work or out-of-scope files are included
4. Tests are meaningful and cover the right boundaries
5. The code follows existing patterns without unnecessary complexity

Use references/batch-reviewer-prompt.md as written.

If the reviewer finds Critical or Important issues, send each issue back to the relevant implementer, refresh its path-scoped patch, and review the batch again. Minor issues may be noted and moved past.

Handling Subagent Questions

Subagents may ask questions before or during implementation. This is good — it means they're thinking rather than guessing.

• Answer clearly and completely
• Provide additional context if needed
• Don't rush them into implementation
• If the question reveals a gap in the plan, that's valuable — note it

Integrating Results

After subagents complete (especially parallel dispatch):

1. Read each summary — understand what changed
2. Capture task patches — use each task's exclusive file list
3. Review the batch — one combined requirements and quality review
4. Run full test suite — verify all changes work together
5. Commit — the coordinator commits the reviewed batch serially
6. Update progress tracking — when the caller uses it

If there are conflicts between parallel results, resolve them manually. Don't dispatch another subagent to merge — that requires too much context.

When Subagents Fail

If a subagent fails a task:

• Don't fix it manually — that pollutes your context
• Dispatch a fix subagent with specific instructions about what went wrong
• If it fails twice, stop and escalate to the human. The requirements or constraints may need revision.