Reformat Code only asked the language server for formatting, so files whose server has no formatting capability (Markdown with marksman, and others depending on the server) could not be formatted.
Languages can now declare an external formatter. Prettier is the first: a managed tool installed on demand, or the project's own node_modules/prettier, an explicit path, or PATH. It runs on the backend copy of the document with the file's path so Prettier resolves the project's config, overrides and ignore files, and its result is applied as one undoable edit. Language servers that format a file keep doing so unless Prettier is preferred in Settings › Languages › Prettier; formatting on save is opt-in. Parsers without range support format the whole file and say so.
Errors carry structured tool data, so a missing Prettier reuses the shared install prompt and Prettier diagnostics or timeouts show as non-sticky notifications.
Fixes#639
Root cause: the tools dir installed typescript@latest, now TypeScript 7 (native port, no typescript.js/tsserver.js/ts.server), so @vue/language-server 3 crashed on ts.server.protocol and restarted forever; Volar 3 hybrid mode also needs tsserver/request forwarding, which we never answered.
Fix: pin TS-as-library servers to typescript@<7 and keep shared deps on uninstall; pick a usable tsdk (setting / bundled / project, --tsdk); bridge tsserver/request to vtsls with @vue/typescript-plugin (null when vtsls is absent); answer workspace/configuration for section ""; stop restarting after 3 consecutive early crashes (IDEA); crash summary starts at the exception line.
Siblings covered: typescript-language-server and svelte-language-server (same TS 7 break), vtsls config, install hints in language TOMLs.
Verified: scoped cargo tests, real-server tests (vue-language-server 3.3.13 + vtsls), in-app on macOS (server running, no crash loop). Not verified on Windows.
Claude-Session: https://claude.ai/code/session_01VUYsdXA2nkF5v6zsC93dpn
l0ng-ai