feat(lsp): add config-driven LSP support (Roblox Luau via luau-lsp)

Add Language Server Protocol integration modeled on opencode's, wired for
this codebase's plain-TypeScript tool/agent architecture.

Core (@dispatch/core):
- lsp/client.ts: LSP/JSON-RPC client over stdio (vscode-jsonrpc) with the
  initialize handshake, didOpen/didChange sync, push + pull diagnostics
  (textDocument/diagnostic, workspace/diagnostic), and a generic request()
  passthrough for hover/definition/references/documentSymbol.
- lsp/server.ts: resolves dispatch.toml [lsp] entries into spawn specs.
  Config-driven only — no builtin registry, no auto-download.
- lsp/manager.ts: process-wide LspManager owning client lifecycles, keyed
  by root+serverID, lazy spawn + reuse + graceful shutdown.
- lsp/language.ts: extension->languageId map incl. .luau -> "luau".
- lsp/diagnostic.ts: error-only <diagnostics> block formatting (1-based).
- tools/lsp.ts: on-demand 'lsp' tool (1-based coords -> 0-based wire).
- write-file.ts: optional onAfterWrite hook for diagnostics-on-write.
- config schema: validate [lsp] block; DispatchConfig.lsp + LspServerConfig.

API (@dispatch/api):
- AgentManager owns one LspManager; per-working-directory server cache
  cleared on config reload; diagnostics appended to write_file results;
  'lsp' tool gated by new perm_lsp setting; shutdownAll on destroy().

Config:
- dispatch.toml: documented, commented [lsp.luau-lsp] Roblox example.

Tests: fake-lsp-server fixture + client/manager/server/diagnostic/schema/
tool/write-hook suites, plus an opt-in real-binary luau-lsp smoke test
(auto-skipped when luau-lsp is absent). 652 pass; biome + 3 typechecks green.

1 files changed, 72 insertions, 0 deletions

diff --git a/packages/core/src/lsp/language.ts b/packages/core/src/lsp/language.ts
new file mode 100644
index 0000000..3e9fe68
--- /dev/null
+++ b/packages/core/src/lsp/language.ts
@@ -0,0 +1,72 @@
+/**
+ * File-extension → LSP `languageId` map.
+ *
+ * The LSP `textDocument/didOpen` notification carries a `languageId` string
+ * that tells the server how to parse the document. This table is a trimmed
+ * port of opencode's `lsp/language.ts`, with one critical addition for this
+ * project: `.luau` → `"luau"`. Roblox Luau sources use the `.luau` extension,
+ * which standard Lua tooling does not recognise — luau-lsp expects the
+ * `"luau"` languageId.
+ *
+ * Extensions are looked up with their leading dot (e.g. `".luau"`). Unknown
+ * extensions fall back to `"plaintext"` at the call site.
+ */
+export const LANGUAGE_EXTENSIONS: Record<string, string> = {
+	// Luau (Roblox) — the reason this module exists. Keep first for visibility.
+	".luau": "luau",
+	".lua": "lua",
+	// A pragmatic subset of common languages, mirroring opencode's table so a
+	// user can point an arbitrary LSP server at this codebase and have the
+	// right languageId reported.
+	".c": "c",
+	".cpp": "cpp",
+	".cc": "cpp",
+	".cxx": "cpp",
+	".h": "c",
+	".hpp": "cpp",
+	".cs": "csharp",
+	".css": "css",
+	".dart": "dart",
+	".go": "go",
+	".html": "html",
+	".htm": "html",
+	".java": "java",
+	".js": "javascript",
+	".jsx": "javascriptreact",
+	".json": "json",
+	".jsonc": "jsonc",
+	".kt": "kotlin",
+	".kts": "kotlin",
+	".md": "markdown",
+	".markdown": "markdown",
+	".php": "php",
+	".py": "python",
+	".rb": "ruby",
+	".rs": "rust",
+	".scss": "scss",
+	".sass": "sass",
+	".sh": "shellscript",
+	".bash": "shellscript",
+	".zsh": "shellscript",
+	".sql": "sql",
+	".svelte": "svelte",
+	".swift": "swift",
+	".toml": "toml",
+	".ts": "typescript",
+	".tsx": "typescriptreact",
+	".mts": "typescript",
+	".cts": "typescript",
+	".vue": "vue",
+	".xml": "xml",
+	".yaml": "yaml",
+	".yml": "yaml",
+	".zig": "zig",
+};
+
+/**
+ * Resolve the LSP `languageId` for a file path's extension, falling back to
+ * `"plaintext"` when the extension is unknown.
+ */
+export function languageIdForExtension(extension: string): string {
+	return LANGUAGE_EXTENSIONS[extension] ?? "plaintext";
+}