feat(nosql): diagnose ORDER BY inside a subquery

[bk201-]

Summary

Azure Cosmos DB NoSQL does not support ORDER BY inside a subquery — FIRST(…),
LAST(…), ARRAY(…), EXISTS(…), scalar (SELECT …), and FROM (SELECT …). The
backend rejects such queries at execution time with HTTP 400, even though:

• the native sql.y grammar accepts them (every subquery embeds a full sql_query,
  which carries an optional ORDER BY), and
• the language reference does not document the restriction.

Because it is a semantic (engine) rule rather than a grammatical one, the parser can't
catch it — so this PR adds a static diagnostic instead, surfacing the error in the editor
before the user runs the query.

Confirmed against production Cosmos DB: every subquery form with ORDER BY returns 400,
while the same subqueries without ORDER BY (and a top-level ORDER BY) work.

Refs Azure/azure-cosmos-db-emulator-docker#311 (originally mis-reported as "FIRST()
unsupported"; the real discriminator is the nested ORDER BY).

Changes

• New detector src/diagnostics/orderByInSubquery.ts — AST walk that flags an
  ORDER BY on any non-root query. Takes the already-parsed AST (no re-parse, no import
  cycle); reports on the ORDER BY clause range.
• Wired into SqlLanguageService.getDiagnostics (single- and multi-query) as
  ORDER_BY_IN_SUBQUERY, severity Error. Exported from the package entry point.
• Tests src/diagnostics/orderByInSubquery.test.ts (15) — FIRST/LAST/ARRAY/EXISTS/
  (SELECT …)/FROM (…), nested and multiple occurrences, negative cases, and service
  integration (single + multi-query offsets).
• Docs/fixtures — note in the ORDER_BY keyword doc; SQ-05/SQ-06 reclassified in
  test-suite.md from "emulator-only known limitation" to a Cosmos DB language
  limitation, with the diagnostic referenced.

Validation

• npm run build (tsc) — clean.
• npm run lint — oxlint + eslint, 0 errors.
• npm run prettier-fix — applied.
• Package tests: 531 passed, 1 skipped; new detector 15/15.

No user-facing string changes outside the diagnostic message.

[github-actions]

🔬 NoSQL language-service integration

Commit: c450cb6
Pull Request: #3148 feat(nosql): diagnose ORDER BY inside a subquery

🧪 Result

• NoSQL integration tests: ✅ success

📥 Artifacts (run)

• nosql-junit-report-1 — 4.6 KB

[github-actions]

🔨 Build, Lint & Test

🔗 Source

• Commit: c450cb6
• Pull Request: #3148 feat(nosql): diagnose ORDER BY inside a subquery

📦 Package Information

• Version: 0.35.1
• Preview: True
• VSIX File: vscode-cosmosdb-0.35.1.vsix
• VSIX Size: 3.34 MB
• Artifact: feat-nosql-order-by-in-subquery-diagnostic-0.35.1-84ff449.zip

🧪 Test Results

• Unit Tests: ✅ success
• Integration Tests (extension host): ✅ success

📥 Artifacts (run)

• feat-nosql-order-by-in-subquery-diagnostic-0.35.1-84ff449 — 3.34 MB

✅ Build Status

Build and local tests passed. See sibling comments below for E2E and NoSQL integration results.