Require HOST explicitly instead of auto-detecting the Wi-Fi IP

Auto-detection (ipconfig getifaddr en0 in Procfile.dev, Socket on the
mailer side) worked against the invariant: the mobile apps hardcode
the IP in the Xcode scheme and ~/.gradle/gradle.properties, so if
Rails silently picked a different one (DHCP rotation, Tailscale or
VPN interface shadowing en0), the three sides diverged without
failing. Require HOST in .env via \${HOST:?...} so `bin/dev` errors
immediately when unset, matching the explicit-IP posture already
needed on mobile.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: dadachi

.env.sample

@@ -1,10 +1,15 @@
-# Copy to .env and edit. Loaded by Foreman when running `bin/dev`.
+# Copy to .env and set HOST to your current Wi-Fi IP, then Foreman
+# auto-loads this when running `bin/dev`.
 #
-# `bin/dev` auto-detects your Wi-Fi IP (via `ipconfig getifaddr en0` on macOS)
-# and binds Rails to it so phones on the same network can reach the dev server.
-# Only set HOST if the auto-detected interface is wrong (wired-primary,
-# Tailscale, etc.). Never use 127.0.0.1, localhost, or 0.0.0.0 — the
-# mobile apps and Rails must agree on the current Wi-Fi IP.
+# Rails, the iOS app, and the Android app must all agree on one
+# reachable address — your host's current Wi-Fi IP. On macOS:
+#
+#   ipconfig getifaddr en0
+#
+# Never use 127.0.0.1, localhost, or 0.0.0.0. When your Wi-Fi IP
+# changes, update HOST here and the matching values in the mobile
+# apps (Xcode scheme NATEMPLATE_API_DOMAIN and Android
+# ~/.gradle/gradle.properties NATEMPLATE_API_DOMAIN).
 
+HOST=192.168.1.6
 PORT=3000
-# HOST=192.168.1.6

CLAUDE.md

@@ -96,7 +96,7 @@ bin/rails dbconsole           # Database console
 - Run tests: `bin/rails test` (205 tests, 402 assertions)
 
 ### Development Server Configuration
-- Server bind and mailer host auto-detect the current Wi-Fi IP (`ipconfig getifaddr en0` in `Procfile.dev`; `Socket.ip_address_list` private IPv4 in `development.rb`) so Rails and mobile apps agree on one reachable address; override with `HOST` in `.env` only if `en0` isn't Wi-Fi. Never use `127.0.0.1`, `localhost`, or `0.0.0.0`.
+- `HOST` (Wi-Fi IP) and `PORT` are required in `.env`; `Procfile.dev` uses `${HOST:?...}` so Rails fails loudly if unset, and `development.rb` uses `ENV.fetch("HOST")` for `action_mailer.default_url_options`. Must match `NATEMPLATE_API_DOMAIN` in the iOS scheme and Android `gradle.properties`. Never `127.0.0.1`, `localhost`, or `0.0.0.0`.
 - Mailbin for email testing at `/mailbin`
 - Admin interface at `/madmin`
 - Tailwind CSS compiled by tailwindcss-rails gem

Procfile.dev

@@ -1 +1 @@
-web: bin/rails server -p ${PORT:-3000} -b ${HOST:-$(ipconfig getifaddr en0)}
+web: bin/rails server -p ${PORT:-3000} -b ${HOST:?HOST is required - set it in .env to your current Wi-Fi IP}

README.md

@@ -85,7 +85,7 @@ bin/setup
 
 ## Running NativeAppTemplate API on your Wi-Fi
 
-`bin/dev` binds Rails to the current Wi-Fi IP (auto-detected via `ipconfig getifaddr en0`), so the dev server is reachable from both the host browser and from any phone on the same network at `http://<wifi-ip>:3000`. To check the IP: `ipconfig getifaddr en0` (or System Settings → Network). If `en0` isn't Wi-Fi on your machine (wired-primary, Thunderbolt networking), copy `.env.sample` to `.env` and set `HOST` to the correct interface's IP. Never use `127.0.0.1`, `localhost`, or `0.0.0.0` — Rails and the mobile apps must agree on the same Wi-Fi IP.
+Copy `.env.sample` to `.env` and set `HOST` to your current Wi-Fi IP. On macOS: `ipconfig getifaddr en0`. `bin/dev` binds Rails to that address so the dev server is reachable from both the host browser and from any phone on the same network at `http://<wifi-ip>:3000`. When your Wi-Fi IP changes, update `HOST` here and the matching `NATEMPLATE_API_DOMAIN` in the mobile apps (Xcode scheme for iOS, `~/.gradle/gradle.properties` for Android) — Rails fails loudly if `HOST` is unset, which keeps the three sides honest. Never use `127.0.0.1`, `localhost`, or `0.0.0.0`.
 
 To run your application, you'll use the `bin/dev` command:
 

config/environments/development.rb

@@ -1,5 +1,4 @@
 require "active_support/core_ext/integer/time"
-require "socket"
 
 Rails.application.configure do
   # Settings specified here will take precedence over those in config/application.rb.
@@ -39,8 +38,7 @@
 
   config.action_mailer.perform_caching = false
 
-  lan_ip = Socket.ip_address_list.find { |a| a.ipv4_private? && !a.ipv4_loopback? }&.ip_address
-  config.action_mailer.default_url_options = {host: ENV.fetch("HOST") { lan_ip }, port: ENV.fetch("PORT", 3000).to_i}
+  config.action_mailer.default_url_options = {host: ENV.fetch("HOST"), port: ENV.fetch("PORT", 3000).to_i}
 
   # Print deprecation notices to the Rails logger.
   config.active_support.deprecation = :log