Answer step defaults to low reasoning effort (issue #134)

Product chose A after the A/B: low cut answer-step reasoning tokens ~45%
and answer time 34s -> 22s with no quality loss. Unset now means "low";
CONSULT_ANSWER_REASONING_EFFORT=off restores the pre-change request body,
and the old "unset keeps the body" guarantee moves to "off".

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/tasks/README.md

@@ -546,3 +546,4 @@
 | `TASK-home-crash-saved-people-20261027.md` | `PROGRESS-home-crash-saved-people-20261027.md` | **#115 首页崩溃**：存过别人的账户一进首页就「页面出错了」——人物列表的资料缺两个字段，启程引导一读就报错；入口补齐默认值（BUG-1464） | 待验收 | `codex/home-crash-saved-people-20261027` |
 | `TASK-upstream-sync9-20261028.md` | `PROGRESS-upstream-sync9-20261028.md` | **第 1 次打回（快速门 1 败：Darakaraka 旧测试锁错值，见 `TASK-upstream-sync9-fix-20261028.md`）** · **#141 上游同步第九轮**：甲批九项已做完并推 `codex/upstream-sync9-20261028`；校正 20 条和 900 条与上一份回放逐条相同；乙批仍等 #137 | 待验收 | `codex/upstream-sync9-20261028` |
 | `TASK-upstream-sync9b-20261028.md` | `PROGRESS-upstream-sync9b-20261028.md` | **第 1 次打回（冻结契约排除清单删了第八轮两条，见 `TASK-upstream-sync9b-fix-20261028.md`）** · **#159 上游同步第九轮乙批（产品选 A）**：Sarpa Drekkana 补成五段、第 22 号 Drekkana 改为 D3 第 8 宫；改冻结文件 `varga.py`，校正 20 + 900 与上一份逐条相同后按 ERR-110 重新冻结。Narayana 小运强度口径（B2）不做，另问产品 | 待验收 | `codex/upstream-sync9b-20261028` |
+| — | — | **#134 咨询答题默认低思考量（产品选 A）**：`CONSULT_ANSWER_REASONING_EFFORT` 不设时默认 `low`，设 `off` 恢复原请求体（Claude 直接执行） | 已推 staging | `codex/answer-effort-default-20261029` |