Shard i528_phase4_judge.py --backend batch submit (un-sharded single batches.create 409s above the 100k cap); drop its batch-judge lint grandfather

Problem

scripts/i528_phase4_judge.py (--backend batch) submits its Anthropic Message Batch un-sharded: a single client.messages.batches.create(...) with all 3 × N requests. On a large i528 job this exceeds the 100k requests/batch API limit and 409s. It is currently grandfathered in scripts/workflow_lint.py BATCH_JUDGE_LEGACY_ALLOWLIST.

This is a DISTINCT bug from the #658 wedge (a deadline-less while True poller): i528_phase4_judge.py --backend batch is submit-only / fire-and-forget — it creates the batch, writes the batch_id to a pending file, and returns; the results are merged by a SEPARATE --backend sync re-run (the merge path is not even in this file). So there is no poller to fix — the latent bug is purely the un-sharded submit.

Surfaced by

The #658 batch-judge incident cleanup (2026-06-25). Both the workflow-improver (lint allowlist) and the issue658_judge_e0_batch.py migration implementer flagged i528_phase4_judge.py as a real pre-#663 judge needing migration, but deferred it because the submit-then-separate-sync-merge protocol is non-trivial to change behavior-preservingly.

Fix

Shard the --backend batch submit — either (a) chunk via the shared _chunk_requests (≤8k/batch) and write multiple batch_ids to the pending file, or (b) route the submit through the shared #663-hardened client (src/explore_persona_space/llm/anthropic_client.py AnthropicBatch / src/explore_persona_space/eval/batch_judge.py). Behavior-preserving constraints to respect: the custom_id format, the --backend sync merge reader, and the 3×-averaging join. After migration, drop scripts/i528_phase4_judge.py from BATCH_JUDGE_LEGACY_ALLOWLIST in scripts/workflow_lint.py (the --check-batch-judge-client guard then enforces it).

Scope / acceptance

• EDIT-ONLY discipline if any i528 batch is ever in flight; do not resubmit a live batch.
• Sharded submit verified by an API-mocked unit test (no live API).
• workflow_lint.py --check-batch-judge-client passes with the allowlist entry removed.