feat: sync agent-browser skill with upstream vercel-labs/agent-browser

Update SKILL.md to match the latest upstream skill from
vercel-labs/agent-browser, adding substantial new capabilities:

- Authentication (auth vault, profiles, session persistence, state files)
- Command chaining, annotated screenshots, diffing
- Security features (content boundaries, domain allowlist, action policy)
- iOS Simulator support, Lightpanda engine, downloads, clipboard
- JS eval improvements (--stdin, -b for shell safety)
- Timeout guidance, config files, session cleanup

Add 7 reference docs (commands, authentication, snapshot-refs,
session-management, video-recording, profiling, proxy-support) and
3 ready-to-use shell templates.

Kept our YAML frontmatter, setup check section, and Playwright MCP
comparison table which are unique to our plugin context.

plugins/compound-engineering/skills/agent-browser/references/proxy-support.md

@@ -0,0 +1,194 @@
+# Proxy Support
+
+Proxy configuration for geo-testing, rate limiting avoidance, and corporate environments.
+
+**Related**: [commands.md](commands.md) for global options, [SKILL.md](../SKILL.md) for quick start.
+
+## Contents
+
+- [Basic Proxy Configuration](#basic-proxy-configuration)
+- [Authenticated Proxy](#authenticated-proxy)
+- [SOCKS Proxy](#socks-proxy)
+- [Proxy Bypass](#proxy-bypass)
+- [Common Use Cases](#common-use-cases)
+- [Verifying Proxy Connection](#verifying-proxy-connection)
+- [Troubleshooting](#troubleshooting)
+- [Best Practices](#best-practices)
+
+## Basic Proxy Configuration
+
+Use the `--proxy` flag or set proxy via environment variable:
+
+```bash
+# Via CLI flag
+agent-browser --proxy "http://proxy.example.com:8080" open https://example.com
+
+# Via environment variable
+export HTTP_PROXY="http://proxy.example.com:8080"
+agent-browser open https://example.com
+
+# HTTPS proxy
+export HTTPS_PROXY="https://proxy.example.com:8080"
+agent-browser open https://example.com
+
+# Both
+export HTTP_PROXY="http://proxy.example.com:8080"
+export HTTPS_PROXY="http://proxy.example.com:8080"
+agent-browser open https://example.com
+```
+
+## Authenticated Proxy
+
+For proxies requiring authentication:
+
+```bash
+# Include credentials in URL
+export HTTP_PROXY="http://username:password@proxy.example.com:8080"
+agent-browser open https://example.com
+```
+
+## SOCKS Proxy
+
+```bash
+# SOCKS5 proxy
+export ALL_PROXY="socks5://proxy.example.com:1080"
+agent-browser open https://example.com
+
+# SOCKS5 with auth
+export ALL_PROXY="socks5://user:pass@proxy.example.com:1080"
+agent-browser open https://example.com
+```
+
+## Proxy Bypass
+
+Skip proxy for specific domains using `--proxy-bypass` or `NO_PROXY`:
+
+```bash
+# Via CLI flag
+agent-browser --proxy "http://proxy.example.com:8080" --proxy-bypass "localhost,*.internal.com" open https://example.com
+
+# Via environment variable
+export NO_PROXY="localhost,127.0.0.1,.internal.company.com"
+agent-browser open https://internal.company.com  # Direct connection
+agent-browser open https://external.com          # Via proxy
+```
+
+## Common Use Cases
+
+### Geo-Location Testing
+
+```bash
+#!/bin/bash
+# Test site from different regions using geo-located proxies
+
+PROXIES=(
+    "http://us-proxy.example.com:8080"
+    "http://eu-proxy.example.com:8080"
+    "http://asia-proxy.example.com:8080"
+)
+
+for proxy in "${PROXIES[@]}"; do
+    export HTTP_PROXY="$proxy"
+    export HTTPS_PROXY="$proxy"
+
+    region=$(echo "$proxy" | grep -oP '^\w+-\w+')
+    echo "Testing from: $region"
+
+    agent-browser --session "$region" open https://example.com
+    agent-browser --session "$region" screenshot "./screenshots/$region.png"
+    agent-browser --session "$region" close
+done
+```
+
+### Rotating Proxies for Scraping
+
+```bash
+#!/bin/bash
+# Rotate through proxy list to avoid rate limiting
+
+PROXY_LIST=(
+    "http://proxy1.example.com:8080"
+    "http://proxy2.example.com:8080"
+    "http://proxy3.example.com:8080"
+)
+
+URLS=(
+    "https://site.com/page1"
+    "https://site.com/page2"
+    "https://site.com/page3"
+)
+
+for i in "${!URLS[@]}"; do
+    proxy_index=$((i % ${#PROXY_LIST[@]}))
+    export HTTP_PROXY="${PROXY_LIST[$proxy_index]}"
+    export HTTPS_PROXY="${PROXY_LIST[$proxy_index]}"
+
+    agent-browser open "${URLS[$i]}"
+    agent-browser get text body > "output-$i.txt"
+    agent-browser close
+
+    sleep 1  # Polite delay
+done
+```
+
+### Corporate Network Access
+
+```bash
+#!/bin/bash
+# Access internal sites via corporate proxy
+
+export HTTP_PROXY="http://corpproxy.company.com:8080"
+export HTTPS_PROXY="http://corpproxy.company.com:8080"
+export NO_PROXY="localhost,127.0.0.1,.company.com"
+
+# External sites go through proxy
+agent-browser open https://external-vendor.com
+
+# Internal sites bypass proxy
+agent-browser open https://intranet.company.com
+```
+
+## Verifying Proxy Connection
+
+```bash
+# Check your apparent IP
+agent-browser open https://httpbin.org/ip
+agent-browser get text body
+# Should show proxy's IP, not your real IP
+```
+
+## Troubleshooting
+
+### Proxy Connection Failed
+
+```bash
+# Test proxy connectivity first
+curl -x http://proxy.example.com:8080 https://httpbin.org/ip
+
+# Check if proxy requires auth
+export HTTP_PROXY="http://user:pass@proxy.example.com:8080"
+```
+
+### SSL/TLS Errors Through Proxy
+
+Some proxies perform SSL inspection. If you encounter certificate errors:
+
+```bash
+# For testing only - not recommended for production
+agent-browser open https://example.com --ignore-https-errors
+```
+
+### Slow Performance
+
+```bash
+# Use proxy only when necessary
+export NO_PROXY="*.cdn.com,*.static.com"  # Direct CDN access
+```
+
+## Best Practices
+
+1. **Use environment variables** - Don't hardcode proxy credentials
+2. **Set NO_PROXY appropriately** - Avoid routing local traffic through proxy
+3. **Test proxy before automation** - Verify connectivity with simple requests
+4. **Handle proxy failures gracefully** - Implement retry logic for unstable proxies
+5. **Rotate proxies for large scraping jobs** - Distribute load and avoid bans