[eric] browser: the agent knows passkey sign-in cannot work here and routes to the password path instead of retrying into Google's generic error (ENG-269)

backend/apps/agents/browser/intervention_copy.py

@@ -9,19 +9,29 @@ learned playbooks, aux adjudication advice) via the catch-all.
 
 from typeguard import typechecked
 
+# Passkeys structurally cannot work here: macOS only exposes Touch ID / iCloud Keychain passkeys to
+# browsers carrying Apple's restricted web-browser entitlement, which this app does not have, so the
+# ceremony always dies as Google's generic "Something went wrong" (ENG-269, measured: uvpaa=false).
+PASSKEY_LINE = (
+    "- Passkey sign-in (Touch ID / iCloud Keychain) does NOT work in this browser and shows "
+    "\"Something went wrong\"; click \"Try another way\" and use the password path instead of retrying.\n"
+)
+
 INTERVENTION_SECTION = (
     "## When you genuinely cannot proceed\n"
     "Use RequestHumanIntervention for:\n"
     "- Login walls (the user thinks they're logged in but the session expired)\n"
     "- Captchas, 2FA prompts, age verification gates\n"
     "- Anything genuinely ambiguous about user intent\n"
+    + PASSKEY_LINE +
     "Don't use it for normal tool failures; try a different approach first.\n\n"
 )
 
 NO_INTERVENTION_SECTION = (
     "## When you genuinely cannot proceed\n"
     "No human is available in this run. If a login wall, captcha, or 2FA gate blocks every "
-    "route, stop and call Done with success=false, naming exactly what blocked you.\n\n"
+    "route, stop and call Done with success=false, naming exactly what blocked you.\n"
+    + PASSKEY_LINE + "\n"
 )
 
 LOOP_AWARENESS_INTERVENTION_PHRASE = (