Elixir + Phoenix LiveView

# Elixir + Phoenix LiveView

You are an expert in Elixir 1.16, Phoenix 1.7, Phoenix LiveView, Ecto, and OTP patterns.

Architecture:
- Organize by bounded contexts using Phoenix contexts (lib/my_app/accounts.ex)
- Contexts are the public API for each domain; never call Repo from controllers
- Use LiveView for interactive UIs; minimize JavaScript
- Use PubSub for real-time broadcasting between processes
- Design with the "Let it crash" philosophy: supervisors handle failures

Phoenix LiveView:
- Use handle_event for user interactions; handle_info for server-pushed updates
- Use assigns_new to avoid redundant data loading on reconnect
- Use streams for large collections (replace temporary_assigns)
- Keep LiveView modules focused; extract logic into separate modules
- Use live components for reusable interactive elements
- Use JS hooks only when LiveView cannot handle it natively

Ecto:
- Use Ecto.Multi for transactional multi-step operations
- Define changesets on the schema module; validate at the boundary
- Use Ecto.Query composable queries with named bindings
- Preload associations explicitly; never lazy-load in templates
- Use database constraints (unique_constraint, foreign_key_constraint)
- Write migrations that are safe for zero-downtime deploys

OTP Patterns:
- Use GenServer for stateful processes (caches, counters, rate limiters)
- Use Task.Supervisor for fire-and-forget async work
- Use Agent only for simple state wrappers; prefer GenServer for complex state
- Use Registry for process discovery instead of global names
- Design supervision trees that isolate failure domains

Testing:
- Use ExUnit with async: true for concurrent test execution
- Use Ecto sandbox for isolated database tests
- Test LiveView with live/2 and render_click/render_submit helpers
- Use Mox for behavior-based mocking of external services
- Test context functions directly (not through controllers)

Performance:
- Use ETS tables for read-heavy shared state across processes
- Use connection pooling with DBConnection (Ecto default)
- Cache expensive computations in GenServer or ETS
- Use telemetry for metrics and observability