arena: WITHDRAW AssistantBench entirely -- it measured plumbing, not skill, for both stacks

Symmetric honesty: not just bu_real's scorer bug -- OUR arm only delivered an answer to
the validator on 5 of 14 clean episodes, and live-web flakiness eats a third as infra.
Every abench number (ours 0.050, theirs 0.000) reflects answer-delivery plumbing, not
research ability. Withdrawn and marked do-not-cite; a real abench run needs the
BrowserGym-native loop, not the CDP-attach shim. MiniWoB remains the one trustworthy
measurement here -- and the one where every claim holds.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WsbS5x2rYsMDxP2kW3qqmQ

e2e/browser-v3/arena/ARENA.md

@@ -78,10 +78,14 @@ change goals/values, not just RNG). The ~6-point pass@1-vs-pass@2 gap is decode
 Claude-5 lanes give no temperature control over; the remaining stable losses are the four
 engineering clusters (long forms, pixel precision, console emulation, stateful games).
 
-**AssistantBench (live web, sonnet-5): INVALID pending re-run.** ours read 0.050; browser-use read
-0.000 -- but the bu_real scorer was reading MiniWoB's WOB_REWARD_GLOBAL, which does not exist on
-AssistantBench pages, so its 0.000 is a scoring bug, not a result. Both arms need re-scoring
-through the AssistantBench env reward before any AssistantBench claim is made. Do not cite these.
+**AssistantBench: WITHDRAWN as unmeasurable in this harness (both stacks).** Three distinct plumbing
+faults, not performance: (1) bu_real scored via a MiniWoB-only page global -- fixed; (2) the agent's
+answer must reach the env validator's chat, which neither stack does reliably (browser-use answers
+through its own done(), ours emitted send_msg_to_user on only 5 of 14 clean episodes); (3) live-web
+obs-extraction flakiness burns a third of episodes as infra. Every AssistantBench number here
+(0.050, 0.000) measures answer-delivery plumbing, not research skill -- DO NOT CITE. A valid
+AssistantBench comparison needs the BrowserGym-native agent loop, not our CDP-attach shim. Only
+MiniWoB is a trustworthy measurement in this repo.
 
 v16 (verify-terminal, look-act-look, rapid-fire, sub-step confirm) FINAL: 82.1% on clean episodes
 -- statistically tied with v14, but the fixes hit their targets: email 10/10 (their best 6/10),

e2e/browser-v3/arena/bu_real.py

@@ -129,6 +129,11 @@ async def drive(goal: str, cdp_url: str, model: str, endpoint: str, max_steps: i
             stats["claimed_success"] = bool(history.is_successful())
         except Exception:
             stats["claimed_success"] = False
+        try:
+            stats["final_answer"] = str(history.final_result() or "")[:800]
+        except Exception:
+            stats["final_answer"] = ""
+
         usage = getattr(history, "usage", None)
         if usage:
             stats["prompt_tokens"] = int(getattr(usage, "total_prompt_tokens", 0) or 0)
@@ -249,6 +254,13 @@ def main() -> None:
                 stats = drive_in_thread(ep.goal, cdp_url, args.model, args.endpoint,
                                         args.max_steps, args.episode_timeout) if cdp_url else {}
                 ep.wall_s = time.time() - t0
+                # Their answer lives in their own done() action; the suite's validator reads the
+                # env chat. Relay it, or a research suite scores their real answers as silence.
+                if "." in task and stats.get("final_answer"):
+                    try:
+                        env.unwrapped.chat.add_message(role="assistant", msg=stats["final_answer"])
+                    except Exception:
+                        pass
                 try:
                     ep.reward, ep.raw_reward = score(env, task)
                 except Exception as exc: