v0.3.5 — Zero-stall re-nudge on zero-reasoning continuation rounds

Fix

• Zero-reasoning continuation rounds are now treated as a zero-stall and re-nudged, instead of being let through on a 516-token total. Per josantonius's report on openai/codex#30364: under --max-n 1, a round 1 of 516 tokens triggers a continuation, but round 2 returning reasoning_tokens=0 was classified as clean and released — leaving the folded reasoning stuck at 516 and the answer still wrong.
• Round ≥2 with reasoning_tokens==0 is now a zero-stall (failed nudge / collapsed continuation): the fold appends another commentary nudge and keeps going, sharing the MAX_CONTINUE budget. Missing usage (None) and round-1 zero-reasoning are deliberately left untouched, matching the PR #5 stance that standalone zero-reasoning has no deterministic fingerprint.
• Budget exhaustion still flushes via the existing path tagged proxy_stopped_reason=max_continue — an answer is never dropped, and the four existing stop labels are byte-for-byte unchanged. test_fold.py adds three cases: stall-then-recover, stall-exhausted, and the round-1 zero-reasoning regression.

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中文说明

本版修复续推轮的零推理 zero-stall：round ≥2 若返回 reasoning_tokens==0，视为 nudge 失败/续推塌缩，再追加一个 commentary nudge 继续，共享 MAX_CONTINUE 预算，不再让 516 token 的总量提前放行。缺失用量（None）与首轮零推理按 PR #5 立场刻意保持不变；预算耗尽仍走 max_continue 路径刷出，答案永不丢弃。