<objective> SOLID Go enforces a modular architecture for Go 1.27+: every feature lives under `internal/modules/[feature]/` (handlers, services, repositories, ports, models) with shared code in `internal/core/`, interfaces (ports) live only in `ports/` directories and stay small (1-3 methods, the Go idiom), functions accept interfaces but return structs, and every exported function carries a godoc comment.

Before writing any new code it requires a DRY check against internal/core/services and internal/core/ports. See solid-principles.md for the overview, the per-principle references for SRP/OCP/LSP/ISP/DIP detail, architecture-patterns.md for hexagonal/modular layout, and the templates for module/service/interface/handler/error/test scaffolding. </objective>

SOLID Go - Modular Architecture

Agent Workflow (MANDATORY)

Before ANY implementation, spawn 3 agents in parallel, one Agent call each with a name:

1. fuse-ai-pilot:explore-codebase - Analyze existing architecture
2. fuse-ai-pilot:research-expert - Verify Go docs via Context7
3. fuse-ai-pilot:sniper - Post-implementation validation

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DRY - Reuse Before Creating (MANDATORY)

Before writing ANY new code:

1. Grep the codebase for similar interfaces, services, or logic
2. Check shared locations: internal/core/services/, internal/core/ports/
3. If similar code exists -> extend/reuse instead of duplicate
4. If code will be used by 2+ features -> create it in internal/core/

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Architecture (Modules MANDATORY)

Layer	Location
Handlers	internal/modules/[feature]/handlers/
Services	internal/modules/[feature]/services/
Repositories	internal/modules/[feature]/repositories/
Ports (interfaces)	internal/modules/[feature]/ports/
Models	internal/modules/[feature]/models/
Shared	internal/core/{services,ports,models}/

NEVER use flat internal/ structure - always internal/modules/[feature]/

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Critical Rules (MANDATORY)

Rule	Value
File limit	FUSE_SOLID_MAX_LINES
Handlers	Thin, delegate to services
Interfaces	ports/ directory ONLY
Godoc	Every exported function documented
Accept interfaces	Return structs
Small interfaces	1-3 methods max (Go idiom)

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Reference Guide

Concepts

Topic	Reference	When to consult
SOLID Overview	solid-principles.md	Quick reference
SRP	single-responsibility.md	Fat structs
OCP	open-closed.md	Adding providers
LSP	liskov-substitution.md	Contracts
ISP	interface-segregation.md	Fat interfaces
DIP	dependency-inversion.md	Injection
Architecture	architecture-patterns.md	Hex/modular

Templates

Template	When to use
module.md	Feature module structure
service.md	Business logic service
interface.md	Port definition
handler.md	HTTP handler
error.md	Custom errors
test.md	Table-driven tests

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Forbidden

Anti-Pattern	Fix
Files over FUSE_SOLID_MAX_LINES	Split by responsibility
Interfaces in impl files	Move to ports/ directory
Fat interfaces (4+ methods)	Split into small interfaces
Flat internal/ structure	Use internal/modules/[feature]/
init() for dependency wiring	Use constructor injection