Add documentation for service dependency checking

- Updated bin/dev --help with SERVICE DEPENDENCIES section
- Added comprehensive documentation in docs/building-features/process-managers.md
- Includes configuration examples, field descriptions, and sample output
- Added security note about command execution
- Documents zero-impact behavior when .dev-services.yml doesn't exist

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: justin808

docs/building-features/process-managers.md

@@ -16,11 +16,12 @@ React on Rails includes `bin/dev` which automatically uses Overmind or Foreman:
 
 This script will:
 
-1. Run Shakapacker's `precompile_hook` once (if configured in `config/shakapacker.yml`)
-2. Set `SHAKAPACKER_SKIP_PRECOMPILE_HOOK=true` to prevent duplicate execution
-3. Try to use Overmind (if installed)
-4. Fall back to Foreman (if installed)
-5. Show installation instructions if neither is found
+1. Check required external services (if `.dev-services.yml` exists)
+2. Run Shakapacker's `precompile_hook` once (if configured in `config/shakapacker.yml`)
+3. Set `SHAKAPACKER_SKIP_PRECOMPILE_HOOK=true` to prevent duplicate execution
+4. Try to use Overmind (if installed)
+5. Fall back to Foreman (if installed)
+6. Show installation instructions if neither is found
 
 ### Precompile Hook Integration
 
@@ -57,6 +58,94 @@ default: &default
 
 See the [i18n documentation](./i18n.md#internationalization) for more details on configuring the precompile hook.
 
+### Service Dependency Checking
+
+`bin/dev` can automatically verify that required external services (like Redis, PostgreSQL, Elasticsearch) are running before starting your development server. This prevents cryptic error messages and provides clear instructions on how to start missing services.
+
+#### Configuration
+
+Create a `.dev-services.yml` file in your project root:
+
+```yaml
+services:
+  redis:
+    check_command: 'redis-cli ping'
+    expected_output: 'PONG'
+    start_command: 'redis-server'
+    install_hint: 'brew install redis (macOS) or apt-get install redis-server (Linux)'
+    description: 'Redis (for caching and background jobs)'
+
+  postgresql:
+    check_command: 'pg_isready'
+    expected_output: 'accepting connections'
+    start_command: 'pg_ctl -D /usr/local/var/postgres start'
+    install_hint: 'brew install postgresql (macOS)'
+    description: 'PostgreSQL database'
+```
+
+A `.dev-services.yml.example` file with common service configurations is created when you run the React on Rails generator.
+
+#### Configuration Fields
+
+- **check_command** (required): Shell command to check if the service is running
+- **expected_output** (optional): String that must appear in the command output
+- **start_command** (optional): Command to start the service (shown in error messages)
+- **install_hint** (optional): How to install the service if not found
+- **description** (optional): Human-readable description of the service
+
+#### Behavior
+
+If `.dev-services.yml` exists, `bin/dev` will:
+
+1. Check each configured service before starting
+2. Show a success message if all services are running
+3. Show helpful error messages with start commands if any service is missing
+4. Exit before starting the Procfile if services are unavailable
+
+If `.dev-services.yml` doesn't exist, `bin/dev` works exactly as before (zero impact on existing installations).
+
+#### Example Output
+
+**When services are running:**
+
+```
+🔍 Checking required services (.dev-services.yml)...
+
+   ✓ redis - Redis (for caching and background jobs)
+   ✓ postgresql - PostgreSQL database
+
+✅ All services are running
+```
+
+**When services are missing:**
+
+```
+🔍 Checking required services (.dev-services.yml)...
+
+   ✗ redis - Redis (for caching and background jobs)
+
+❌ Some services are not running
+
+Please start these services before running bin/dev:
+
+redis
+   Redis (for caching and background jobs)
+
+   To start:
+   redis-server
+
+   Not installed? brew install redis (macOS) or apt-get install redis-server (Linux)
+
+💡 Tips:
+   • Start services manually, then run bin/dev again
+   • Or remove service from .dev-services.yml if not needed
+   • Or add service to Procfile.dev to start automatically
+```
+
+#### Security Note
+
+⚠️ Commands in `.dev-services.yml` are executed during `bin/dev` startup. Only add commands from trusted sources. Consider adding `.dev-services.yml` to `.gitignore` if it contains machine-specific paths or sensitive information.
+
 ## Installing a Process Manager
 
 ### Overmind (Recommended)

lib/react_on_rails/dev/server_manager.rb

@@ -331,6 +331,7 @@ def help_options
         end
         # rubocop:enable Metrics/AbcSize
 
+        # rubocop:disable Metrics/AbcSize
         def help_customization
           <<~CUSTOMIZATION
             #{Rainbow('🔧 CUSTOMIZATION:').cyan.bold}
@@ -341,8 +342,24 @@ def help_customization
             #{Rainbow('•').yellow} #{Rainbow('Procfile.dev-prod-assets').green.bold}     - Production-optimized assets (port 3001)
 
             #{Rainbow('Edit these files to customize the development environment for your needs.').white}
+
+            #{Rainbow('🔍 SERVICE DEPENDENCIES:').cyan.bold}
+            #{Rainbow('Configure required external services in').white} #{Rainbow('.dev-services.yml').green.bold}#{Rainbow(':').white}
+
+            #{Rainbow('•').yellow} #{Rainbow('bin/dev').white} #{Rainbow('checks services before starting (optional)').white}
+            #{Rainbow('•').yellow} #{Rainbow('Copy from').white} #{Rainbow('.dev-services.yml.example').green.bold} #{Rainbow('to get started').white}
+            #{Rainbow('•').yellow} #{Rainbow('Supports Redis, PostgreSQL, Elasticsearch, and custom services').white}
+            #{Rainbow('•').yellow} #{Rainbow('Shows helpful errors with start commands if services are missing').white}
+
+            #{Rainbow('Example .dev-services.yml:').white}
+            #{Rainbow('  services:').cyan}
+            #{Rainbow('    redis:').cyan}
+            #{Rainbow('      check_command: "redis-cli ping"').cyan}
+            #{Rainbow('      expected_output: "PONG"').cyan}
+            #{Rainbow('      start_command: "redis-server"').cyan}
           CUSTOMIZATION
         end
+        # rubocop:enable Metrics/AbcSize
 
         # rubocop:disable Metrics/AbcSize
         def help_mode_details