Drop LanguageService dependency from core and CLI

[johnsoncodehk]

What

Replace LinterContext = { typescript, languageService, languageServiceHost } with { typescript, program: () => Program } and drop ts.createLanguageService from the CLI worker. Linting now runs end-to-end against ts.Program only, with no LanguageService anywhere on the path.

// before
interface LinterContext {
  typescript: typeof import('typescript');
  languageService: ts.LanguageService;
  languageServiceHost: ts.LanguageServiceHost;
}

// after
interface LinterContext {
  typescript: typeof import('typescript');
  program: () => ts.Program;
}

The thunk (vs a stable instance) lets callers swap programs mid-session — --fix rewrites a file, flips programDirty, the next lint() reads a freshly built program. Each lint() reads the thunk once at the top so program identity stays stable for that file's pass.

Why

tsgo (@typescript/native-preview) exposes Snapshot / Project / Program / Checker — no LanguageService equivalent. The pre-3.2 LS-coupled core was the largest blocker for tsgo integration; with the surface shrunk to a Program thunk, tsgo's Project.program slots straight in.

This also pays for itself today: ts.createLanguageService pulls in completion / refactor / navigation / watcher machinery that the linter never touched.

CLI worker (the bulk of the diff)

packages/cli/lib/worker.ts no longer instantiates a LanguageService. It now:

• Builds a ts.CompilerHost directly. Overrides getSourceFile for (a) setParentNodes: true (compat-eslint walks Node.parent), (b) SourceFile.version content-hash stamping (BuilderProgram requires it), and (c) Vue / MDX / Astro virtualisation via the active language plugin.
• Hand-rolls the Volar setup (createLanguage + resolveFileLanguageId) instead of calling proxyCreateProgram. The latter applies decorateProgram which wraps getSemanticDiagnostics to mutate SourceFile.text in place — after the AST is parsed — so diagnostic spans land at characters that no longer match the AST. Master got away with this via LS-side decorateLanguageServiceHost; we can't.
• Maintains a process-level sourceFileCache: Map<string, ts.SourceFile> shared across projects in the same CLI invocation. Pre-3.2 the LS instance survived setup() calls and reused lib + shared node_modules types across projects; with the LS gone, this restores parity (warm npm run lint over 7 tsconfigs: 1.09-1.14s, on par with master).

resolveCompletions plugin hook

The one place that genuinely needed LanguageService was @tsslint/config's ignore plugin — it wrapped getCompletionsAtPosition to suggest // @tsslint-ignore-style comments and rule IDs. Replaced with:

interface PluginInstance {
  resolveCompletions?(file, position, entries: CompletionEntry[]): CompletionEntry[];
}

Linter.getCompletions(fileName, position) aggregates across plugins. CLI doesn't call it; typescript-plugin wraps the host LS's getCompletionsAtPosition and merges in linter.getCompletions(...). Same UX, no LS reach-through inside @tsslint/config.

Public API breakage

• LinterContext.languageService removed
• LinterContext.languageServiceHost removed
• LinterContext.program: () => Program added
• PluginInstance.resolveCompletions added (optional)

Affects custom LinterContext consumers and any plugin reaching for ctx.languageService directly. The path forward is ctx.program() for type info, resolveCompletions for completion contributions.

Tests

New:

• packages/core/test/completions.test.ts — resolveCompletions aggregator (7 cases)
• packages/cli/test/program-host.test.ts — version stamping, setParentNodes, fileTextOverrides flow, oldProgram rebuild (6 cases)
• packages/cli/test/meta-frameworks.test.ts — spawns the real CLI on fixtures/meta-frameworks for --vue-project / --mdx-project / --astro-project / --vue-vine-project, asserts no-console fires on each framework's script content

Existing tests adjusted for the new context shape. Dify CLI cold lint: bit-identical to master (2961 passed / 1867 errors / 9 messages).