fix(browser): use AGENT_BROWSER_ARGS instead of AGENT_BROWSER_CHROME_FLAGS

[ambition0802]

Summary

The browser tool was setting AGENT_BROWSER_CHROME_FLAGS when sandbox bypass was needed, but agent-browser only reads AGENT_BROWSER_ARGS. This caused the --no-sandbox injection to be a silent no-op on Ubuntu 23.10+ / AppArmor systems, resulting in "No usable sandbox" errors.

Changes

1. Fixed env var name in _run_browser_command():

   • Changed AGENT_BROWSER_CHROME_FLAGS → AGENT_BROWSER_ARGS
   • Updated comments to reference issue [Bug]: Headless VM fails to use browser: tools/browser_tool.py writes AGENT_BROWSER_CHROME_FLAGS but agent-browser reads AGENT_BROWSER_ARGS --sandbox-bypass injection is a no-op #23496

2. Added sandbox bypass to _run_chrome_fallback_command():

   • This function was missing the sandbox detection logic entirely
   • Now applies the same root/AppArmor detection and AGENT_BROWSER_ARGS injection
   • Uses consistent logger prefix (browser fallback:)

Root Cause

Commit 74c1b94 added sandbox bypass detection and wrote to AGENT_BROWSER_CHROME_FLAGS, but the agent-browser CLI only consumes AGENT_BROWSER_ARGS. The env var mismatch meant the flags were never actually passed to Chromium on launch.

Testing

• Python syntax validation: ✅
• Logic verified against agent-browser documented env vars

Affected Systems

• Root user execution (Docker/VPS deployments)
• Ubuntu 23.10+ with AppArmor userns restrictions
• Non-root users under systemd or unprivileged containers

Fixes #23496
Related: #15765

[alt-glitch]

Competing with #21659 and #20014 for the same fix (AGENT_BROWSER_CHROME_FLAGS → AGENT_BROWSER_ARGS). All address #23496. #23532 was previously closed as duplicate.

[teknium1]

Thanks for identifying the agent-browser environment-variable mismatch.

Problems

• The primary replacement is already on current main: tools/browser_tool.py:2405-2416 injects comma-separated AGENT_BROWSER_ARGS; commit 8ed2ef6f46e9642acfba57b4b8da893a574ecfd0 made that correction.
• The fallback half remains relevant, but it should be rebased conceptually rather than copied verbatim. Current main centralizes root/Docker/AppArmor detection in _needs_chromium_sandbox_bypass() at tools/browser_tool.py:301-314; the PR's duplicated fallback condition omits Docker and uses the pre-fix space-separated argument form.
• Current tests cover the detection helper (tests/tools/test_browser_open_timeout.py:31-51) and fallback annotations, but not the fallback subprocess environment.

Suggested changes

• Salvage the fallback-only fix at tools/browser_tool.py:1055: reuse _needs_chromium_sandbox_bypass() and inject AGENT_BROWSER_ARGS=--no-sandbox,--disable-dev-shm-usage with the same pre-set-variable guard as tools/browser_tool.py:2405-2416.
• Add a regression test that captures the fallback subprocess.Popen(..., env=...) call.

Automated hermes-sweeper review.