docs(api): record the os:check decision for client-sdk.mdx, and fence its JSX as tsx

content/docs/api/client-sdk.mdx

@@ -25,6 +25,41 @@ The `@objectstack/client` is the official TypeScript client for ObjectStack. It
 pnpm add @objectstack/client
 ```
 
+{/*
+ CONTRIBUTOR NOTE — none of this page's TypeScript fences carries an
+ `os:check` marker, and that is a recorded decision rather than an omission.
+
+ `check:skill-examples` compiles marked blocks per SURFACE. `content/docs/**`
+ belongs to the "skills + docs" surface, whose resolution dir and `paths` map
+ are derived from `@objectstack/spec` alone — and `@objectstack/spec` does not
+ depend on `@objectstack/client`. So a marker on any fence that imports the SDK
+ reds with TS2307 "Cannot find module '@objectstack/client'" — a
+ surface-resolution gap, not doc-vs-SDK drift.
+
+ Every other fence is a deliberate continuation fragment: Quick Start
+ establishes `client` once and each later block continues that implied context,
+ so a marker there reds with TS2304 "Cannot find name 'client'". Making either
+ class compile would mean hand-declaring the SDK's own types, or injecting
+ casts into prose whose subject IS the real API — pinning each example to
+ itself and teaching worse code than the page teaches now.
+
+ Measured on this page (all 13 fences marked, then reverted): 128 diagnostics,
+ every one TS2307 / TS2304 / TS18004 / TS18046 / TS2591 / TS7006 / TS7026 /
+ TS2875. Not one was a doc-vs-SDK divergence.
+
+ The React Hooks block near the end is fenced tsx, not typescript, because it
+ IS JSX: the gate writes every block out with its fence's own extension, and
+ JSX in a .ts file is a syntax error. That reaches past this page — tsc stops
+ at syntax errors and never runs the semantic pass, so one such block would
+ suppress type-checking for every marked block across skills/ and
+ content/docs/ (measured here: 128 semantic diagnostics collapse to 0). Please
+ do not retag it back.
+
+ The marker becomes worth adding here the day the docs surface can resolve
+ `@objectstack/client` — the same condition recorded in
+ content/docs/kernel/runtime-services/data-service.mdx.
+*/}
+
 ## Quick Start
 
 ```typescript
@@ -636,7 +671,7 @@ For React applications, use `@objectstack/client-react`:
 pnpm add @objectstack/client-react
 ```
 
-```typescript
+```tsx
 import { ObjectStackProvider, useClient, useQuery } from '@objectstack/client-react';
 import { ObjectStackClient } from '@objectstack/client';