feat: allow local Postgres for development/test

Gemfile

@@ -7,8 +7,10 @@ gem "propshaft"
 # Use sqlite3 as the database for Active Record. Also in :desktop so the bundled
 # desktop app (which always runs on SQLite, never Postgres) ships the adapter.
 gem "sqlite3", ">= 2.1", groups: [ :development, :test, :desktop ]
-# Use postgresql as the database for production
-gem "pg", group: :production
+# Use postgresql as the database for production, and opt-in for local
+# development/test via DB_ADAPTER=postgresql or DATABASE_URL (SQLite -> Postgres
+# migration). Requires libpq (e.g. `brew install libpq` / postgresql).
+gem "pg", groups: [ :development, :test, :production ]
 # Use the Puma web server [https://github.com/puma/puma]
 gem "puma", ">= 5.0"
 # Bundle JavaScript via esbuild [https://github.com/rails/jsbundling-rails]

config/database.yml

@@ -4,7 +4,16 @@
 #   Ensure the SQLite 3 gem is defined in your Gemfile
 #   gem "sqlite3"
 #
-<% adapter = ENV["DATABASE_URL"].to_s.then { |u| u.empty? ? "sqlite3" : URI.parse(u).scheme } %>
+<%
+  # Adapter selection (development/test):
+  #   1. DATABASE_URL set        -> use its scheme (postgres cutover, CI, etc.)
+  #   2. DB_ADAPTER=postgresql   -> local Postgres, no URL required
+  #   3. otherwise               -> sqlite3 (zero-config default)
+  database_url = ENV["DATABASE_URL"].to_s
+  raw_adapter  = database_url.empty? ? ENV.fetch("DB_ADAPTER", "sqlite3") : URI.parse(database_url).scheme
+  # Normalize the "postgres" URL scheme to Rails' registered "postgresql" adapter name.
+  adapter      = raw_adapter == "postgres" ? "postgresql" : raw_adapter
+%>
 default: &default
   adapter: <%= adapter %>
   pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>
@@ -13,18 +22,35 @@ default: &default
   variables:
     journal_mode: WAL
     synchronous: normal
+  <% elsif database_url.empty? %>
+  encoding: unicode
+  host: <%= ENV.fetch("DATABASE_HOST", "localhost") %>
+  username: <%= ENV.fetch("DATABASE_USERNAME", "collavre_user") %>
+  password: <%= ENV["DATABASE_PASSWORD"] %>
   <% end %>
 
 development:
   <<: *default
+  <% if adapter == "sqlite3" %>
   database: storage/development.sqlite3
+  <% elsif database_url.empty? %>
+  database: <%= ENV.fetch("DATABASE_NAME", "collavre_db") %>
+  <% else %>
+  url: <%= database_url %>
+  <% end %>
 
 # Warning: The database defined as "test" will be erased and
 # re-generated from your development database when you run "rake".
 # Do not set this db to the same as development or production.
 test:
   <<: *default
+  <% if adapter == "sqlite3" %>
   database: storage/test.sqlite3
+  <% elsif database_url.empty? %>
+  database: <%= ENV.fetch("TEST_DATABASE_NAME", "collavre_test") %>
+  <% else %>
+  url: <%= database_url %>
+  <% end %>
 
 production:
   primary:

env.template

@@ -7,6 +7,15 @@ KAMAL_REGISTRY_PASSWORD=
 RAILS_MASTER_KEY=
 SECRET_KEY_BASE=
 # DATABASE_URL=sqlite3:storage/production-primary.sqlite3
+# Local development/test on Postgres (SQLite -> Postgres migration). Leave unset
+# for the default SQLite. Set DB_ADAPTER=postgresql to use the local collavre_db
+# without a DATABASE_URL; the vars below override the built-in local defaults.
+# DB_ADAPTER=postgresql
+# DATABASE_HOST=localhost
+# DATABASE_USERNAME=collavre_user
+# DATABASE_PASSWORD=
+# DATABASE_NAME=collavre_db
+# TEST_DATABASE_NAME=collavre_test
 PORT=80
 GEMINI_API_KEY=
 # empty for default