SKILL.md

name	code-structure-cleanup
description	Guides behavior-preserving boundary cleanup after a feature works. Use when code has duplicated mechanics, repeated API calls, mixed contracts/policy/adapters, privileged effects inside domain logic, deep imports, or a growing god module; use to decide ownership across shared records, policy, services, ports, adapters, and presentation.
hints	- Run cleanup AFTER the feature works, never during feature development. - Extract shared mechanics only after 2+ callers; split mixed responsibilities even when a module has one caller. - Keep domain rules (auth, error classification, status transitions) in actions. - Keep dependency-free shared records in the lowest safe package and privileged effects behind owning-package ports. - Replace one caller first, verify, then migrate the rest. - Keep the diff small and focused on the feature area only.

Code Structure Cleanup & Service Layer Architecture

Overview

AI agents often take the easiest path: they create new functions instead of reusing existing ones. A feature can work while still leaving behind duplicated logic, inconsistent validation, and repeated API calls that future agents will struggle to debug.

The fix is a two-layer architecture: actions orchestrate domain rules (the "why/when"), while a service layer centralizes reusable mechanics (the "how"). Run the cleanup pass after the feature works — not before, and not during.

When to Use

• A feature works but the code has duplicated mechanics across multiple files.
• Multiple callers perform the same low-level operation (email sending, sandbox creation, API calls, data parsing).
• The agent created similar helper functions in different files.
• A bug fix in one flow was not propagated to other flows doing the same thing.

When NOT to use: A cohesive single-purpose module merely because it is long, or a speculative abstraction with no ownership problem. Do not use this as permission to redesign the whole app.

Boundary Shape

Use only the layers the domain has earned:

contracts/      dependency-free records and stable vocabulary
domain/         invariants and state transitions
policy/         deterministic decisions
ports/          capabilities required from storage, process, provider, or host
services/       use-case orchestration over policy and ports
adapters/       filesystem, database, provider, process, Electron, or transport effects
presentation/   host-specific view models and UI

Do not create every folder mechanically. Split when a file mixes owners, when a host effect leaks into deterministic policy, or when a shared record sits above one of its consumers in the dependency graph. Keep existing public entrypoints as thin compatibility barrels until all maintained consumers migrate.

The Service Layer Pattern

Orchestration Layer (Actions)          Service Layer (Shared Mechanics)
├── owns business rules                ├── owns reusable operations
├── owns state transitions             ├── owns provider/SDK interactions
├── owns auth/ownership checks         ├── owns command execution details
├── owns failure classification        ├── owns health checks / readiness
├── owns retries / user-facing errors  └── returns structured results
└── calls service functions

Decision rule:

• "What this product flow means" → keep in actions
• "How to do this operation reliably" → move to service layer

Designing Service Functions

Design as capability blocks, not monoliths. Each function should:

• Accept all required data as explicit parameters (no hidden global state)
• Return structured outputs — e.g., { ready, previewUrl, proxyPort }
• Never reach into the database or domain state directly
• Make failure explicit (structured results, not swallowed errors)

// Good: composable blocks — each caller picks what it needs
createManagedSandbox(...)
prepareRepo(...)
detectPackageManager(...)
installDependencies(...)
runBuildCommand(...)

// Bad: one god function that hides all control flow
doEverythingForSandbox(...)

Cleanup Process

Step 1: Run the Cleanup Prompt

The feature is working. Now do a code-structure cleanup pass.

Goal:
- Find duplicated runtime mechanics, repeated API calls, repeated parsing, repeated validation.
- Move repeated mechanics into reusable service-layer functions/modules.
- Keep domain policy (auth, status transitions, error classification) in the calling route/action.
- Do not change user-facing behavior.
- Keep the diff small.

Process:
1. Inspect the files touched by the feature.
2. Identify repeated logic and name the duplication clearly.
3. Propose the smallest service-layer extraction.
4. Implement it.
5. Run the relevant tests/typechecks.
6. Summarize exactly what got simpler.

Step 2: Migrate Incrementally

1. Write the flow in action code first — establish clear behavior.
2. Mark repeated operational chunks across callers.
3. Extract repeated non-domain chunks to a service function, or separate mixed contracts/policy/host effects behind the smallest earned boundary.
4. Replace one caller first → verify tests pass → replace remaining callers.
5. Run typecheck, lint, and confirm all flows still work.

Example: Email Service

// emailService.ts — shared mechanics (the "how")
export async function sendWelcomeEmail(params: { to: string; name: string }) {
  const html = `<h1>Welcome ${params.name}</h1>`;
  await emailProvider.send(params.to, "Welcome", html);
}

// userSignup.ts — orchestration (the "when" — different business rule)
if (user.marketingOptIn) {
  await sendWelcomeEmail({ to: user.email, name: user.name });
}

// adminInvite.ts — orchestration (same mechanic, different domain rule)
await sendWelcomeEmail({ to: invitee.email, name: invitee.name });

Common Rationalizations

Rationalization	Reality
"I'll clean it up later"	Later never comes. AI agents copy existing patterns — duplicated code compounds with every new feature.
"It's only in two places"	Two callers is exactly when to extract. Three callers means the window for clean extraction is closing.
"Cleanup will change behavior"	It should not. Behavior-changing cleanup is a bug fix or refactor — do it separately.
"I'll just refactor the whole module while I'm here"	Unscoped cleanup creates risky diffs and noisy PRs. Stay focused on the feature area.
"The service should handle business logic too"	Services own mechanics, not decisions. Auth, error classification, and policy stay in actions.

Red Flags

• A bug fix applied in one flow was not applied to other flows doing the same thing.
• Helper functions with the same logic scattered across action files.
• Service functions that directly mutate database tables or domain state.
• A single "do-everything" service function hiding all control flow.
• Cleanup and feature development mixed in the same PR.
• Extracting logic used by only one caller (premature abstraction).

Verification

After completing the cleanup pass, confirm:

• User-facing behavior is unchanged (existing tests still pass).
• Duplicated mechanics were reduced — callers now share the extracted function.
• Calling files became simpler, not more complex.
• Domain policy (auth, transitions, error classification) remained in actions.
• Typecheck and lint passed.
• Diff is focused on the feature area — no unrelated changes mixed in.