Phoenix JSON API

Canonical FP bar: docs/fcis-engineering-rules.md — Functional Core, Imperative Shell: pure domain modules; side effects at edges. Keep LiveView/controller callbacks thin; delegate business rules to contexts/pure modules.

RULES — Follow these with no exceptions

1. Use the :api pipeline — don't mix HTML and JSON pipelines; API routes skip CSRF and sessions 2. Render errors as structured JSON — {:error, changeset} must become {"errors": {...}} 3. Version APIs via URL prefix (/api/v1/) — not headers; URL versioning is visible and cacheable 4. Use FallbackController for consistent error handling — every action returns {:ok, result} or {:error, reason}

Build Workflow

Follow these steps in order when constructing a new API endpoint: