Add SDK persistence and configurable edge location

- Add external SDK installation (wp-content/twilio-sdk/) that survives
  WordPress plugin updates
- Add install-twilio-sdk-external.sh script for external SDK setup
- Update SDK loading to check external location first, internal fallback
- Add post-update detection hook to warn if SDK was deleted
- Add configurable Twilio Edge Location setting (default: roaming)
- Fix US calls failing due to hardcoded Sydney edge location

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

README.md

@@ -8,11 +8,20 @@ This plugin **requires** the Twilio PHP SDK v8.7.0 to function. The plugin will
 
 ## Quick Installation
 
-1. **Install the Twilio SDK** (Required):
+1. **Install the Twilio SDK** (Required - Recommended Method):
+   ```bash
+   chmod +x install-twilio-sdk-external.sh
+   ./install-twilio-sdk-external.sh
+   ```
+
+   This installs the SDK to `wp-content/twilio-sdk/` which **survives WordPress plugin updates**. The plugin will automatically detect and use this external SDK.
+
+   **Alternative Method** (SDK will be deleted during plugin updates):
    ```bash
    chmod +x install-twilio-sdk.sh
    ./install-twilio-sdk.sh
    ```
+   This installs the SDK inside the plugin folder. You'll need to reinstall the SDK after each plugin update.
 
 2. **Test the SDK installation**:
    ```bash
@@ -23,6 +32,7 @@ This plugin **requires** the Twilio PHP SDK v8.7.0 to function. The plugin will
    - Go to **Twilio** → **Settings**
    - Enter Account SID and Auth Token
    - Configure default phone numbers
+   - Set Twilio Edge Location (for browser phone - see Browser Phone Setup below)
 
 4. **Set up Phone Numbers** in Twilio Console:
    - Configure webhook URLs for voice and SMS
@@ -333,8 +343,20 @@ Comprehensive redesign of hold, transfer, and requeue functionality with profess
 2. **Configure in WordPress**:
    - Go to **Twilio** → **Settings**
    - Enter TwiML App SID
+   - **Set Twilio Edge Location**: Select the edge location closest to your users (IMPORTANT)
+     - **Auto-select closest (Recommended)**: Automatically selects the best edge
+     - **US East (Ashburn)**: For East Coast USA users
+     - **US West (Umatilla)**: For West Coast USA users
+     - **Europe - Ireland (Dublin)**: For European users
+     - **Europe - Germany (Frankfurt)**: For Central European users
+     - **Singapore**: For Southeast Asian users
+     - **Sydney**: For Australian users
+     - **Tokyo**: For Japanese users
+     - **Sao Paulo**: For South American users
    - Save settings
 
+   **Note**: Selecting the wrong edge location can cause calls to fail immediately. If you're experiencing browser phone connection issues, verify your edge location is appropriate for your region.
+
 3. **Access Browser Phone** (Admin Only):
    - Navigate to **WordPress Admin** → **Twilio** → **Browser Phone**
    - Select caller ID from available numbers
@@ -432,14 +454,34 @@ Access the full browser phone interface at: **WordPress Admin → Twilio → Bro
 - **Login Required**: Users must be logged in to access browser phone functionality
 - Check TwiML App SID is configured in WordPress admin settings
 
+#### Browser Phone Calls Failing Immediately
+If browser phone calls disconnect immediately or show HANGUP errors:
+- **Check Edge Location Setting**: Go to **Twilio** → **Settings** → **Twilio Edge Location**
+- **US Users**: Should use "Auto-select closest" (roaming), "US East (Ashburn)", or "US West (Umatilla)"
+- **International Users**: Select the edge location closest to your region
+- **Problem**: Wrong edge location causes gateway to immediately reject calls
+- **Solution**: Change edge location setting and try the call again (no restart needed)
+
 #### "Twilio SDK classes not available"
+
+**Recommended Solution** (SDK survives plugin updates):
 ```bash
-# Reinstall SDK
+# Install SDK to external location
+./install-twilio-sdk-external.sh
+# Test installation
+php test-sdk.php
+```
+
+**Alternative Solution** (will need reinstall after plugin updates):
+```bash
+# Install SDK inside plugin folder
 ./install-twilio-sdk.sh
 # Test installation
 php test-sdk.php
 ```
 
+**After WordPress Plugin Update**: If you get this error after updating the plugin and used the internal SDK method, you'll need to reinstall the SDK. This won't happen if you use the external SDK method.
+
 #### Calls Not Routing to Queues
 - Verify queue exists and is active
 - Check agent group has members
@@ -551,7 +593,19 @@ All webhooks are REST API endpoints under `/wp-json/twilio-webhook/v1/`:
 
 ## Version History
 
-### v2.3.0 (Current - September 2025) - ENTERPRISE READY
+### v2.8.9 (Current - January 2026) - SDK PERSISTENCE & BROWSER PHONE FIXES
+- **SDK PERSISTENCE**: External SDK installation option that survives WordPress plugin updates
+  - New installation script: `install-twilio-sdk-external.sh` installs SDK to `wp-content/twilio-sdk/`
+  - Automatic detection: Plugin checks external SDK location first, falls back to internal
+  - Post-update warnings: Notifies if SDK was deleted during plugin update
+  - Zero downtime: Phone system continues working through plugin updates
+- **BROWSER PHONE FIX**: Resolved US calls failing immediately with HANGUP errors
+  - Made Twilio Edge Location configurable (was hardcoded to Sydney)
+  - New setting: Twilio Edge Location with 8 options (roaming/auto-select, ashburn, umatilla, dublin, frankfurt, singapore, sydney, tokyo, sao-paulo)
+  - Default: "roaming" (auto-select closest edge for optimal performance)
+  - Critical fix: US users can now make calls successfully (were failing with Sydney edge)
+
+### v2.3.0 (September 2025) - ENTERPRISE READY
 - **SECURITY ENHANCEMENT**: Removed frontend browser phone interface, moved to admin-only access for enhanced security
 - **ASSET REDUCTION**: Eliminated 108KB of frontend assets (browser-phone-frontend.js and CSS files)
 - **SHORTCODE SECURITY**: Browser phone shortcode now provides secure redirect with authentication checks
@@ -611,4 +665,4 @@ This plugin integrates with Twilio services and requires a Twilio account.
 
 ---
 
-**Enterprise Ready v2.3.0** - Extension transfers, browser phone compatibility, and automatic agent management now production-ready with comprehensive reliability improvements.
+**Production Ready v2.8.9** - SDK persistence through plugin updates and configurable edge locations ensure zero-downtime phone operations.