diff --git a/AGENTS.md b/AGENTS.md
index ce255fd..2d22da3 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -109,3 +109,10 @@ uv run playwright install chromium
 
 Run with `uv run pytest -m e2e`. Excluded from the default fast suite
 via the `e2e` marker.
+
+**Sandbox note:** Chromium needs Mach-port IPC on macOS, which the
+Claude Code sandbox blocks. When running e2e tests from a sandboxed
+agent session, pass `dangerouslyDisableSandbox: true` on the
+`uv run pytest -m e2e` invocation (the symptom of a sandboxed run is
+a `FATAL` Chromium crash with `Permission denied (1100)` on Mach port
+rendezvous, not a missing-binary or network error).