Add browser js_error recovery guidance (#975)

* Add browser js_error recovery guidance

* Add docs regression test for browser js_error guidance

tests_v2/test_browser_skill_js_error_docs.py

@@ -0,0 +1,35 @@
+#!/usr/bin/env python3
+"""Regression checks for cmux-browser js_error troubleshooting docs."""
+
+import sys
+from pathlib import Path
+
+sys.path.insert(0, str(Path(__file__).parent))
+from cmux import cmuxError
+
+
+ROOT = Path(__file__).resolve().parents[1]
+SKILL = ROOT / "skills/cmux-browser/SKILL.md"
+
+
+def _must(cond: bool, msg: str) -> None:
+    if not cond:
+        raise cmuxError(msg)
+
+
+def main() -> int:
+    skill = SKILL.read_text(encoding="utf-8")
+
+    _must("## Troubleshooting" in skill, "Expected Troubleshooting section in cmux-browser skill")
+    _must("### `js_error` on `snapshot --interactive` or `eval`" in skill, "Expected js_error troubleshooting heading")
+    _must("cmux browser surface:7 get url" in skill, "Expected get url recovery step")
+    _must("cmux browser surface:7 get text body" in skill, "Expected get text body recovery step")
+    _must("cmux browser surface:7 get html body" in skill, "Expected get html body recovery step")
+    _must("when `snapshot --interactive` or `eval` returns `js_error`" in skill, "Expected js_error fallback guidance")
+    _must("navigate to a simpler intermediate page" in skill, "Expected simpler-page fallback guidance")
+
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())