docs: close the four gaps Codex found in the issue #11 design

The embedding client does not go through the chat onion -- embed() runs
its own chain down to _emit(), which builds a ChatRequest on the spot
and so far only fills session_id and parent_call_id. Changing chat()
alone would have left every embed row with empty dimensions, which is
exactly what the issue's second request asks for.

The bigger find: the draft claimed serialization could not fail because
the entry check already restricts values to scalars. It can. A float
passes a naive type check and json.dumps writes it as the literal NaN,
which is not valid JSON and which JSONB rejects; the failure then lands
in the emitter's degrade path and turns a caller's input error into
silently dropped telemetry. Now rejected at the entry with isfinite and
again at serialization with allow_nan=False.

Also states the validation runs at both public entries, not just chat(),
and adds the RLS template the design had promised but never wrote down.

research-wiki/designs/issue11-caller-dimensions.md

@@ -19,4 +19,5 @@ date: 2026-08-17
 - **超限报错而非静默丢弃**: Langfuse 的"value 超 200 字符直接丢弃"**不抄**,违反 P5。报错点在 `chat()` 入口而非遥测写入点——遥测层一切失败都被降级成 warning,校验放那里等于没有校验(同 `overlay` 保护键先例)。
 - **不进缓存 key**: `cache_namespace` 已是必填的租户隔离维度并已进 key(ARCH §7.5),重复;且进 key 会让存量缓存全量冷启动。
 - **被否决备选**: 纯 `meta` JSON 不提列(RLS 静默退化);可配置提升列白名单(多下游共表静默写错类型);复用 `cache_namespace` 传租户(缓存隔离单位 ≠ 数据归属,会让下游无法表达"同租户多命名空间");`tenant_id` 混在 `meta` 里当约定 key(拼错不报错,静默降级成普通维度)。
+- **审查留痕(Codex,2026-08-17)**: 报 4 项,逐条核实后**全部采纳**。① `embed()` 路径覆盖不足——`EmbeddingClient` 不走 chat 洋葱,`_emit()` 在 `embedding.py:360` 现场构造 `ChatRequest`,只改 chat 会导致 embed 行维度恒空,恰好落空 issue 第 2 条诉求;② **非有限 float 会击穿"序列化不可达"论断**——`json.dumps` 把 `nan` 写成 `NaN` 字面量(非合法 JSON,PG JSONB 拒收),失败会被降级吞成 warning,即调用方输入错误转化为静默丢遥测;实测确认后改为入口 `math.isfinite` + 序列化 `allow_nan=False` 双层收口;③ 校验入口表述只写 `chat()`,与双路径 API 不一致;④ §4.5 承诺"提供 RLS 模板"却只给了索引模板,已补上含 `FORCE`/`USING`+`WITH CHECK`/`NULLIF(current_setting(...))` 的完整定稿。第 ② 条的推翻过程已写进正文 §6,因为"入口校验完备 ⇒ 下游不可能失败"这个推理模式容易复发。
 - **另开议题**: `_BACKFILL` 自动 ALTER 是否应降级为默认关闭(Hangfire `EnableHeavyMigrations` 先例、APScheduler 4.x 版本不认识即拒绝启动)——与本 issue 同源但属独立架构变更,按反 gold-plating 不纳入本次。