docs: design caller-defined dimensions for the telemetry table

Issue #11 asks for a tenant column so a multi-tenant caller can isolate
rows in the database. Widened to caller-defined dimensions in general,
but only the caller's own: model name and friends keep their existing
columns, and the library writes nothing into the new container.

Two independent findings force tenant_id to be a real column rather than
a key inside JSON. An RLS policy on meta->>'tenant_id' parses fine, but
the planner discards statistics for non-LEAKPROOF functions under RLS,
and ->> is not marked leakproof; the pgsql-general report that hit this
ended up moving the indexed column out of JSONB. Separately, the planner
has no usable statistics for JSONB at all -- @> falls back to a
hardcoded 0.1% selectivity.

A configurable promoted-column whitelist is rejected: when two
downstreams infer different types for the same key, the second
ADD COLUMN is silently skipped by IF NOT EXISTS and the wrong type is
written from then on, without an error.

The library stops at the column plus a documented policy template. It
must never enable RLS itself -- with no matching policy that is
default-deny, which would silently fail every write for the two
downstreams that are not multi-tenant.

research-wiki/index.md

@@ -1,8 +1,8 @@
 # Research Wiki 索引
 
-> 自动生成，更新时间：2026-08-16 09:50 UTC
+> 自动生成，更新时间：2026-08-17 09:53 UTC
 
-## design (28)
+## design (30)
 - [2026-07-20-m1-core-design](designs/2026-07-20-m1-core-design.md) `design:2026-07-20-m1-core-design`
 - [2026-07-20-m2-distributed-design](designs/2026-07-20-m2-distributed-design.md) `design:2026-07-20-m2-distributed-design`
 - [2026-07-21-m25-resilience-design](designs/2026-07-21-m25-resilience-design.md) `design:2026-07-21-m25-resilience-design`
@@ -16,6 +16,7 @@
 - [2026-08-06-governance-backend-error-design](designs/2026-08-06-governance-backend-error-design.md) `design:2026-08-06-governance-backend-error-design`
 - [2026-08-06-issue8-stall-budget-design](designs/2026-08-06-issue8-stall-budget-design.md) `design:2026-08-06-issue8-stall-budget-design`
 - [2026-08-16-issue10-error-body-retention-design](designs/2026-08-16-issue10-error-body-retention-design.md) `design:2026-08-16-issue10-error-body-retention-design`
+- [2026-08-17-issue11-caller-dimensions-design](designs/2026-08-17-issue11-caller-dimensions-design.md) `design:2026-08-17-issue11-caller-dimensions-design`
 - [est_tokens 解耦: 拆分限流预扣与遥测用量兜底(issue #2)](designs/est-tokens-decoupling.md) `design:est-tokens-decoupling`
 - [GatewaySettings 装配校验补齐(第二轮)](designs/settings-invariants-round-2.md) `design:settings-invariants-round-2`
 - [GatewaySettings 跨字段不变量守卫的生效范围](designs/settings-invariant-guards.md) `design:settings-invariant-guards`
@@ -30,6 +31,7 @@
 - [建表前先探测,判死只认「确定写不进去」](designs/issue9-telemetry-ddl-probe.md) `design:issue9-telemetry-ddl-probe`
 - [推理开关能力建模与 reasoning_tokens 采集(issue #5 + #6)](designs/2026-08-02-thinking-capability-design.md) `design:2026-08-02-thinking-capability-design`
 - [治理后端故障归位为 scope 级不可用(Issue #7)](designs/governance-backend-error.md) `design:governance-backend-error`
+- [调用方自定义维度设计(issue #11)](designs/issue11-caller-dimensions.md) `design:issue11-caller-dimensions`
 - [采样参数透传设计(issue #4)](designs/sampling-params.md) `design:sampling-params`
 
 ## finding (12)