feat(vnext): sketch relation completion contracts (#183)

## Summary

- add package-private provisional contracts for relation catalog search,
epochs, path authority, dialect-owned decoding/rendering, completion
results, and session lifecycle
- migrate catalog search paths from dot-joined strings to decoded
identifier-component paths with quote provenance
- add a runtime-free marimo-shaped core fixture covering atomic
document/context/region transactions, providers, subscriptions,
completion results, and negative type guarantees
- add a separate CodeMirror fixture requiring explicit disposal for
custom rich-info resources

These declarations intentionally remain outside the `./vnext` public
export surface until the complete vertical slice, two provider shapes,
hostile decoding, packed marimo integration, and lifecycle/performance
gates pass.

## Design constraints

- provider authoring is strongly typed, but runtime ingress will be
erased to `unknown` and strictly decoded
- providers return decoded role-bearing canonical paths and positive
addressability evidence; only dialect runtime data may decode SQL
identifiers or render insertion text
- provider requests contain only bounded catalog/query data; provider
cancellation is passed separately
- consumer results do not expose epochs, scheduler work IDs, deadlines,
configuration identity, or terminal-vs-soft loading causes
- every `catalog-loading` issue carries a bounded remaining intent lease
- custom CodeMirror rich info must return `{ dom, destroy }`, enabling
late-result draining and React-root unmounting

## Validation

- `pnpm run typecheck`
- `pnpm exec oxlint`
- `pnpm run test:integrity`
- `pnpm test` — 1,248 passed, 1 expected failure
- `pnpm run test:browser` — 7 passed
- `pnpm run test:package`
- changed coverage — 100% statements, branches, functions, and lines
- exact-head adversarial approval from SQL/API and marimo ergonomics
reviewers at `d5a38af2804c928bc8acf7f7a0ae91a759f3de24`

Part of #169.

<!-- This is an auto-generated description by cubic. -->
---
## Summary by cubic
Adds provisional, strongly typed contracts for SQL relation completion,
including catalog search, dialect decoding/rendering, completion
items/results, and session lifecycle. Migrates identifier handling to
decoded `SqlIdentifierPath` components and adds a disposable CodeMirror
resolver for custom info. Part of #169.

- New Features
- Relation catalog contracts: search request/response, epochs, coverage
(complete/partial/paginated), provider reports.
- Dialect runtime for identifier decode/render and CTE identifier
equality.
- Completion model for CTEs and catalog relations, with issues and
ready/unavailable/cancelled/failed results.
- Session API with transactional updates, completion, change events, and
disposal.
  - CodeMirror `SqlCompletionInfoResolver` returning `{ dom, destroy }`.
- Export `SqlIdentifierComponent` and `SqlIdentifierPath` from
`src/vnext/index.ts`.

- Migration
- Replace dot-joined search paths with `SqlIdentifierPath`; use
`SqlIdentifierComponent` for all name parts.
- Providers are async, take `AbortSignal` separately, and return decoded
paths (no SQL insert text); rendering moves to the dialect runtime.
- Embedded regions are readonly; document updates must pass the full
`embeddedRegions` set.
- Incomplete completion lists must include at least one issue;
`catalog-loading` issues include `remainingIntentLeaseMs`.

<sup>Written for commit 2d0bade.
Summary will update on new commits.</sup>

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Author: Light2Dark

src/vnext/codemirror/relation-completion-types.ts

@@ -0,0 +1,19 @@
+import type { SqlRelationCompletionItem } from "../relation-completion-types.js";
+
+// Provisional CodeMirror-only boundary; the framework-independent core stays DOM-free.
+export interface SqlCompletionInfoResolverContext {
+  readonly signal: AbortSignal;
+}
+
+export interface SqlDisposableCompletionInfo {
+  readonly dom: Node;
+  readonly destroy: () => void;
+}
+
+export type SqlCompletionInfoResolver = (
+  item: SqlRelationCompletionItem,
+  context: SqlCompletionInfoResolverContext,
+) =>
+  | SqlDisposableCompletionInfo
+  | null
+  | Promise<SqlDisposableCompletionInfo | null>;

src/vnext/index.ts

@@ -16,6 +16,8 @@ export type {
   SqlDocumentReplacement,
   SqlDocumentSession,
   SqlDocumentUpdate,
+  SqlIdentifierComponent,
+  SqlIdentifierPath,
   SqlLanguageService,
   SqlLanguageServiceOptions,
   SqlPlainData,