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, 68 insertions, 0 deletions

diff --git a/packages/core/src/lsp/server.ts b/packages/core/src/lsp/server.ts
new file mode 100644
index 0000000..1fb002e
--- /dev/null
+++ b/packages/core/src/lsp/server.ts
@@ -0,0 +1,68 @@
+import { type ChildProcessWithoutNullStreams, spawn } from "node:child_process";
+import type { LspServerConfig } from "../types/index.js";
+import type { LspServerHandle } from "./client.js";
+
+/**
+ * A resolved, ready-to-spawn LSP server derived from a `dispatch.toml`
+ * `[lsp.<id>]` entry. Config-driven only — dispatch ships no builtin server
+ * registry and performs no auto-download (unlike opencode). The declared
+ * executable (`command[0]`) must already be on PATH.
+ */
+export interface ResolvedLspServer {
+	id: string;
+	/** Extensions (with leading dot) this server attaches to, e.g. `".luau"`. */
+	extensions: string[];
+	/** Launch the server over stdio rooted at `root`. */
+	spawn(root: string): LspServerHandle;
+}
+
+/**
+ * Spawn a child process for an LSP server over stdio. Inherits `process.env`
+ * (so a PATH-resident `rojo` is visible to luau-lsp's sourcemap autogenerate)
+ * and merges any `env` from the server config on top.
+ */
+function spawnServer(
+	command: string[],
+	cwd: string,
+	env: Record<string, string> | undefined,
+	initialization: Record<string, unknown> | undefined,
+): LspServerHandle {
+	const [cmd, ...args] = command;
+	if (!cmd) throw new Error("LSP server command is empty");
+	const proc = spawn(cmd, args, {
+		cwd,
+		env: { ...process.env, ...env },
+		stdio: ["pipe", "pipe", "pipe"],
+	}) as ChildProcessWithoutNullStreams;
+	return {
+		process: proc,
+		...(initialization ? { initialization } : {}),
+	};
+}
+
+/**
+ * Turn the parsed `dispatch.toml` `lsp` block into a list of spawnable
+ * servers. Disabled entries are dropped. Entries with no `command`/`extensions`
+ * are skipped defensively (the config validator already enforces these, but we
+ * guard here too so a hand-built config object can't crash the manager).
+ */
+export function resolveServersFromConfig(
+	lsp: Record<string, LspServerConfig> | undefined,
+): ResolvedLspServer[] {
+	if (!lsp) return [];
+	const servers: ResolvedLspServer[] = [];
+	for (const [id, entry] of Object.entries(lsp)) {
+		if (entry.disabled) continue;
+		if (!entry.command || entry.command.length === 0) continue;
+		if (!entry.extensions || entry.extensions.length === 0) continue;
+		const command = entry.command;
+		const env = entry.env;
+		const initialization = entry.initialization;
+		servers.push({
+			id,
+			extensions: entry.extensions,
+			spawn: (root: string) => spawnServer(command, root, env, initialization),
+		});
+	}
+	return servers;
+}