create-feature-slice

---

name: create-feature-slice description: Adds a complete vertical-slice feature to a service in this repo — feature folder, command or query record, co-located validator, handler (or in-endpoint logic), route, and a declarative authorization gate. Three variants selected by the service's declared endpoint framework: FastEndpoints without MediatR (handler in the endpoint), Carter + MediatR, and Minimal APIs + MediatR. Use when adding a new feature to Submission, Review, Journals, Production, Auth, or ArticleHub — read the service's CLAUDE.md for its framework first. user-invocable: true

Create Feature Slice

Adds one vertical-slice feature to a service: a feature folder holding the command or query, its co-located validator, and the handler — plus a thin endpoint and a declarative authorization gate. A feature is always a folder; there is never a shared Controllers/ or Validators/ god-folder (endpoints-3).

The endpoint framework is a per-service decision (endpoints-1). Read the target service's CLAUDE.md Endpoint framework line first, then follow the matching variant — do not carry one service's shape into another.

Step 0 — Pick the variant

Read src/Services/{Service}/CLAUDE.md. Its Endpoint framework line selects one of three variants; each has a copy-ready template with full code for every phase below. Then skim one existing feature in that same service — the closest sibling operation — for its exact current idioms (folder nesting, base types, response shape) before writing: the template gives the shape, the neighbour confirms this service's live form.

Declared framework	Variant	Services	Handler shape	Template
FastEndpoints (no MediatR)	A	Journals, Production, Auth	logic in the endpoint's HandleAsync — no handler file (endpoints-2)	templates/fastendpoints.md
Carter + MediatR	B	Review (ArticleHub is read-only)	ICarterModule shim dispatches via ISender to an IRequestHandler	templates/carter-mediatr.md
Minimal APIs + MediatR	C	Submission	static Map extension dispatches via ISender to an IRequestHandler	templates/minimal-api-mediatr.md

The framework inventory is architecture-reference.md §4; the rules are endpoints-1 and endpoints-2.

Where the feature folder lives

• Variant A (FastEndpoints): everything is colocated in the API project — {Service}.API/Features/{Area}/{Operation}/ holds the endpoint + command + validator together (endpoints-3).
• Variants B and C (MediatR): the command + validator + handler live in {Service}.Application/Features/{Area}/{Operation}/; the thin endpoint shim lives in {Service}.API/Endpoints/ (endpoints-2, endpoints-3). Submission uses a flat Features/{Operation}/; Review nests under an {Area}/ (for example Articles/).

Phases (every variant)

Each phase states the binding rule and its registry row; the concrete per-variant code is in the template from Step 0.

1. Feature folder — create Features/{Area}/{Operation}/ in the project named above. One folder per feature; never a god-folder (endpoints-3).

2. Command / query record

   • Article-scoped write — inherit the service's ArticleCommand base (its own Features/.../_Shared/ArticleCommand.cs, which is ArticleCommandBase<ArticleActionType> plus the CQRS marker). The base self-computes audit and provenance: ArticleId, ActionType, Action, CreatedOn, and CreatedById are all [JsonIgnore] and pipeline-set — only Comment and your own payload fields are wire-settable. Override the abstract ActionType with this feature's enum value. Never add a settable CreatedById or CreatedOn to the wire contract; provenance is pipeline-computed, never client-trusted (appcqrs-1).
   • Non-article command/query (for example CreateJournal, GetArticle) — a plain record. MediatR variants mark it ICommand<TResponse> or IQuery<TResponse>; FastEndpoints request records carry no marker.
   • The ICommand<T> / IQuery<T> markers express read/write intent in the type system only — no pipeline behavior branches on them (appcqrs-5).

3. Validator (co-located) — in the same file as the record. The base type follows the framework (endpoints-4): MediatR uses AbstractValidator<T>; FastEndpoints uses Validator<T> (or the project-local BaseValidator<T> in Production). Article-scoped commands extend the service's ArticleCommandValidator<T> base, which supplies the ArticleId greater-than-zero rule. Validators are auto-discovered — MediatR via AddValidatorsFromAssemblyContaining (already wired in Application/DependencyInjection.cs), FastEndpoints via assembly scan — so do not register the validator by hand.

4. Handler / in-endpoint logic — same body shape everywhere: load the aggregate, call its existing domain behavior method, SaveChangesAsync, return the response.

   • Variant A — the logic goes in the endpoint's HandleAsync; there is no handler file (endpoints-2).
   • Variants B and C — write an IRequestHandler<TCommand, TResponse> in the feature folder; the endpoint only dispatches via ISender. Handlers are MediatR-assembly-scanned — no DI edit.
   • No role checks and no IsInRole in the handler or domain body — authorization is the endpoint's job (endpoints-5).

5. Endpoint + route

   • REST-resource-first URL; append a :verb RPC suffix for non-CRUD actions (/articles/{articleId:int}:approve), applied identically across all three frameworks. Plain CRUD stays verb-less (POST /articles, GET /articles/{id}) (namingx-4).
   • Route-id binding: bind {articleId} from the route into the command before dispatch — Minimal API uses command with { ArticleId = articleId }, Carter sets command.ArticleId = articleId.
   • Registration: FastEndpoints endpoints are attribute-routed and auto-discovered by UseCustomFastEndpoints(), and Carter modules are auto-discovered by MapCarter() — both need zero manual wiring. Minimal API is the exception: add one line to EndpointRegistration.MapAllEndpoints().

6. Authorization gate — declarative, at the endpoint boundary only (endpoints-5):

   • Role-gated article write — the two-layer RequireRoleAuthorization(Role.X, ...) (Minimal API / Carter) or [Authorize(Roles = Role.X)] (FastEndpoints). The RequireRoleAuthorization extension stacks RequireRole plus an ArticleRoleRequirement resource check; never call bare RequireRole (security-2).
   • Read-only aggregate endpoint (ArticleHub, or any plain authenticated read) — single-layer .RequireAuthorization() or [Authorize]: authentication only, no resource gate (security-2).

Response mapping (Mapster)

Handlers and endpoints move data between the wire, the domain, and the response with Mapster's .Adapt<T>() — the same tool inbound and outbound:

• Inbound (wire record to entity), when the shapes line up: var journal = command.Adapt<Journal>(); (Journals CreateJournal).
• Outbound (entity to DTO): return new GetArticleResponse(article.Adapt<ArticleDto>()); (Submission GetArticle); journal.Adapt<JournalDto>() (Journals GetJournal).

Eligibility test — bare .Adapt<T>() or a config? Use a bare .Adapt<T>() only when member names and nesting line up and Mapster's flattening convention (a nested Journal.Name resolves to a flat JournalName) does the rest. The moment a member name differs, a value object needs a factory, inheritance is involved, or a property must be ignored, register the rule in an IRegister config in the service's Mappings/ folder (assembly-scanned by AddMapsterConfigsFromAssemblyContaining) — never hand-map field-by-field in the handler. Real rules from Submission.Application/Mappings/RestEndpointMappings.cs:

config.NewConfig<ArticleActor, ActorDto>().Include<ArticleAuthor, ActorDto>();   // inheritance
config.NewConfig<IArticleAction<ArticleActionType>, ArticleAction>()
      .Map(dest => dest.TypeId, src => src.ActionType);                          // renamed member
config.ForType<string, EmailAddress>().MapWith(src => EmailAddress.Create(src)); // value-object factory

Flattening caveat: the convention is silent — a nested member that does not resolve to a matching flat name is left at its default, with no error. When an outbound ArticleDto/JournalDto comes back with an unexpectedly empty field, suspect a flattening miss and add an explicit .Map(...) rather than trusting the convention.

Binding rules

1. A feature is a folder; never a Controllers/ or Validators/ god-folder (endpoints-3).
2. The endpoint framework comes from the service CLAUDE.md, not from preference (endpoints-1).
3. Article provenance (ArticleId, CreatedById, CreatedOn, Action) is [JsonIgnore] and pipeline-computed — never a wire field (appcqrs-1).
4. Commands and queries carry ICommand<T> / IQuery<T> markers in MediatR services; nothing branches on them (appcqrs-5).
5. The MediatR request pipeline is already registered once per service in Application/DependencyInjection.cs — do not re-register behaviors; rely on it to stamp CreatedById before validation runs (appcqrs-2). For the pipeline itself — the behaviors, their order, and how to add one — see the cqrs-patterns skill.
6. Authorization is declarative at the endpoint; zero role logic in a handler or domain body (endpoints-5).
7. Non-CRUD routes take a :verb suffix (namingx-4).

What this skill does NOT do

• Create or modify the domain aggregate or its behavior method. The handler calls an existing behavior method; if it is missing, add it with the aggregate/domain skill first.
• Wire integration events, consumers, gRPC contracts, or file storage — separate concerns with their own skills.
• Register pipeline behaviors, validators, or handlers by hand — all are already auto-wired (appcqrs-2).
• Add or reorder MediatR pipeline behaviors, or go deeper on command/query dispatch — that is the cqrs-patterns skill; this one only slots a feature into the existing pipeline.
• Split a FastEndpoints endpoint that has outgrown its file into endpoint + sibling request/response types — that is the extract-endpoint-types skill, the natural follow-up once a Variant A slice grows.

Lessons

When this skill misfires — a service's real feature shape has drifted from a template, a cited row is now wrong, or you hit a case a variant does not cover — capture it in docs/skill-backlog.md (or the running feature's lessons.md) so the skill gets a consolidating fix, not a silent one-off workaround.