Development

Multiplayer game development principles. Architecture, networking, synchronization.

When the user wants to optimize post-signup onboarding, user activation, first-run experience, or time-to-value. Also use when the user mentions "onboarding flow," "activation rate," "user activation," "first-run experience," "empty states," "onboarding checklist," "aha moment," or "new user experience." For signup/registration optimization, see signup-flow-cro. For ongoing email sequences, see email-sequence.

Show this worktree's creature and the branch-hygiene signals behind its mood. Use when the user asks about their pet or types /pets.

Wire pets into this machine's Codex config, or say how to install the binary. Use when the user asks to set pets up for Codex or types /pets-setup.

Install the Opslane browser SDK, verify the first event, and connect GitHub, Slack, source maps, and MCP.

Phase 2 (Development), step 1 of product-playbook. Decide the tech stack + tools + key architecture decisions, benchmarked to current-year options and chosen against the project's own constraints. Use at the start of building, or run /architect "what stack", "tech decisions", "how should we build this". Writes the Architecture section of PRODUCT.md. Run /structure next.

Evaluate a code change for web-security flaws — OWASP Top 10:2025 classes as source-review classes, taint signals from source to sink, and a per-language sink appendix. Use after writing or editing code that handles input, auth, data access, templating, deserialization, or external requests; when asked to security-review a change, check for injection/XSS/SSRF/authz flaws, or evaluate the security of what was just written. Report-only, candidate-tier by construction.

Author an implementation plan as a file, in whatever permission mode the session is already in, without entering plan mode and without implementing what it plans. Use when asked to build, write, draft, or revise a plan, design doc, or implementation strategy for work that happens later, or a living tracker for a long piece of work that spans many sessions. Every claim in the plan cites the tree or is labeled unverified, and the plan is checked before its path is reported. It never offers to s...

Define a Protean event upcaster — a class that transforms old event payloads to match the current schema version, enabling event schema evolution without breaking stored events. Upcasters extend BaseUpcaster, implement an upcast(data) method, and are registered with @domain.upcaster(event_type=EventClass, from_version='v1', to_version='v2'). The framework automatically chains individual upcasters and applies them lazily during deserialization. Use when the user asks to 'create an upcaster', '...

Define a Protean subscriber - a domain element that consumes messages from external message brokers and acts as an anti-corruption layer at the domain boundary. Subscribers listen to named broker streams, receive raw dict payloads (not typed domain events), and translate external data into domain operations. Unlike event handlers which react to internal domain events, subscribers react to messages arriving from outside the bounded context via external message brokers. Use when you need to con...

Introduce domain events to replace direct cross-aggregate calls, tight coupling, and synchronous side effects. Detects transaction boundary violations — handlers that modify multiple aggregates — and refactors them into event-driven flows with proper aggregate isolation. Use when the user says "introduce events", "add events", "decouple aggregates", "fix transaction boundary", "two aggregates in one handler", "make it event-driven", "break the coupling", or when an audit identifies transactio...

Extract value objects from primitive fields in Protean aggregates, entities, and commands. Detects primitive obsession — raw String/Float/Integer fields representing domain concepts that deserve their own type — and refactors them into proper value objects. Use when the user says "extract value object", "create a value object from these fields", "fix primitive obsession", "these fields should be a VO", "refactor money fields", "extract address", or when an audit identifies primitive obsession...

Define a Protean query - an immutable DTO representing a read intent against a projection (read model). Queries carry the parameters needed to fetch data on the read side of CQRS and are answered by query handlers via domain.dispatch(). Queries are associated with a projection (not an aggregate) and are named for what they fetch (GetOrderById, SearchOrders, ListActiveUsers). Use when you need to define a read request, model a query parameter object, build the read side of CQRS, or when the us...

Define a Protean projector - a specialized event handler that maintains read-optimized projections (read models) by listening to domain events from one or more aggregates. Projectors are always associated with a projection via projector_for and use the @on decorator (alias for @handle) to process specific event types. Unlike generic event handlers, projectors explicitly target a projection and can listen to multiple stream categories or aggregates. Use when you need to build a read model, mai...

Enrich Protean commands and events with cross-cutting metadata using command enrichers and event enrichers. Enrichers are domain-level functions that return a dict merged into a message's metadata.extensions - useful for tenant ids, request/correlation context, actor info, and audit data that should ride along with every command or event without polluting the payload. Use @domain.command_enricher for commands and @domain.event_enricher for events. Use when you need to attach context to messag...

Define a Protean domain event - an immutable fact representing a state change in the business domain. Events capture meaningful changes to aggregates and enable decoupled communication between system components. Events are always associated with aggregates and are named in past-tense (OrderPlaced, CustomerRegistered). Use when you need to record what happened in your domain, when you want to communicate state changes to other parts of the system, when the user asks to "create an event", "defi...

Define a Protean event handler - a class that consumes domain events raised by aggregates and orchestrates side effects such as syncing state across aggregates, sending notifications, or triggering downstream processes. Event handlers are always associated with an aggregate via part_of and use the @handle decorator to process specific event types. They follow a fire-and-forget pattern and do NOT return values. Also covers cross-aggregate synchronization - coordinating state between aggregates...

Build custom field validators for Protean domain elements — callable classes that validate individual field values. Covers format validation (email, phone, URL, SKU, credit card, etc.), using Protean's built-in RegexValidator, creating parameterized/configurable validators, composing multiple validators on a single field, and customizing error messages. Use when the user asks to "create a validator", "add custom validation", "validate email format", "validate phone number", "build a format ch...

Define a Protean command - an immutable DTO representing an intent to change aggregate state. Commands encapsulate the data necessary to perform a specific action and are processed by command handlers. Commands are always associated with aggregates and are named with imperative verbs (PlaceOrder, RegisterUser, CancelReservation). Use when you need to define an action or operation that changes domain state, when the user asks to "create a command", "define a command", "add a command", when imp...

Define a Protean command handler - a class responsible for receiving domain commands and orchestrating state changes in aggregates. Command handlers extract data from commands, load or create aggregates, invoke aggregate methods, and persist state changes. They are always associated with one aggregate via part_of and use the @handle decorator to process specific command types. Use when you need to process a command, handle a domain action, write a command handler, implement the handler for a ...

Define a Protean application service - a stateless orchestration layer that coordinates use cases between external callers (API controllers, CLI handlers, background jobs) and the domain model. Application services load aggregates, invoke domain methods, and persist results without containing business logic themselves. They are always associated with one aggregate via part_of and use the @use_case decorator for automatic UnitOfWork wrapping. Unlike command handlers, application services are i...

Define FastAPI API endpoints for a Protean application. Endpoints are thin adapters at the domain boundary that translate HTTP requests into domain commands and hand them off via domain.process(). They contain NO business logic. Use when you need to create an API endpoint, define a route, add a REST endpoint, expose a command via HTTP, build a FastAPI handler, connect HTTP to the domain, create a POST/PUT/DELETE endpoint, or wire an HTTP request to a domain command.

Build a complete vertical slice in Protean - the full command flow from command definition through handler, aggregate mutation, event raising, and event handler reaction. This is the most common workflow for adding a new feature. Use when the user asks to "add a use case", "add a feature", "create a command flow", "implement a vertical slice", "add a new action", "build an end-to-end flow", "add command processing", or when they describe actions like "users should be able to place orders", "a...

Build a complete external integration flow in Protean using subscribers. Subscribers consume messages from external systems via broker streams and translate them into domain actions using the anti-corruption layer (ACL) pattern. Use when the user asks to "add an external integration", "consume external events", "handle webhook events", "integrate with an external system", "add a subscriber flow", "build an anti-corruption layer", "translate external messages", "process broker messages", or wh...