Feature Request: Add stealth mode via AGENT_BROWSER_STEALTH environment variable

Problem

Users are encountering bot detection when automating websites (see #53). While #34 and PR #35 propose adding --args for basic anti-detection flags like --disable-blink-features=AutomationControlled, this only addresses a subset of detection vectors.

Modern bot detection systems (Cloudflare, DataDome, PerimeterX, reCAPTCHA, etc.) check for many more signals:

• navigator.webdriver property
• WebGL vendor/renderer fingerprinting
• Plugin/mime type enumeration
• Chrome runtime properties
• Inconsistent browser feature detection
• And many more

Proposed Solution

Add stealth mode support via the AGENT_BROWSER_STEALTH environment variable, integrating playwright-stealth or similar techniques.

Usage:

# Enable stealth mode for the session
export AGENT_BROWSER_STEALTH=true
agent-browser open https://example.com

Why environment variable?

Since agent-browser is designed to be used by AI agents (not human users), adding a --stealth flag to every command is impractical. The environment variable approach:

• Is set once before the daemon starts
• Applies to the entire browser session automatically
• Requires no changes to how AI agents issue commands
• Aligns with existing env var patterns (AGENT_BROWSER_HEADED, AGENT_BROWSER_ARGS, etc.)

What stealth mode would do

• Apply playwright-stealth evasions to the browser context
• Mask navigator.webdriver
• Fix WebGL fingerprinting inconsistencies
• Spoof plugin/mime types
• Apply other standard anti-detection patches

Why Not Just Use AGENT_BROWSER_ARGS?

PR #35's --args / AGENT_BROWSER_ARGS approach is useful but limited:

• --disable-blink-features=AutomationControlled only addresses one detection vector
• Some evasions require JavaScript injection at context creation, not just launch flags
• Users would need to know and maintain all the right configurations
• Stealth plugins bundle tested, maintained evasion techniques

Implementation Notes

• Disabled by default to keep current behavior unchanged
• Apply evasions in browser.ts when creating the browser context
• playwright-stealth is lightweight (~50KB) and well-maintained

Related

• #53 - User unable to pass verification
• #34 / PR #35 - Basic --args support for launch flags