fix: make the sampling invariant test actually enforce the constraint

The test passed overlay and sampling as separate objects while production
aliases them, so an in-place mutation slipped through it. Also syncs the
telemetry schema page and adds the missing postgres round-trip assertion.

research-wiki/index.md

@@ -1,6 +1,6 @@
 # Research Wiki 索引
 
-> 自动生成，更新时间：2026-07-31 17:01 UTC
+> 自动生成，更新时间：2026-08-01 01:58 UTC
 
 ## design (20)
 - [2026-07-20-m1-core-design](designs/2026-07-20-m1-core-design.md) `design:2026-07-20-m1-core-design`
@@ -56,7 +56,7 @@
 - [采样参数透传实现计划(issue #4)](plans/sampling-params-plan.md) `plan:sampling-params-plan`
 
 ## schema (1)
-- [表结构: llm_calls(遥测 20 字段)](schemas/llm-calls.md) `schema:llm-calls`
+- [表结构: llm_calls(遥测 21 字段)](schemas/llm-calls.md) `schema:llm-calls`
 
 ## metric (2)
 - [OCR 治理调用成功率与错误分类分布](metrics/ocr-call-success.md) `metric:ocr-call-success`