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, 28 insertions, 2 deletions

diff --git a/packages/core/src/tools/write-file.ts b/packages/core/src/tools/write-file.ts
index aa69c86..8a73352 100644
--- a/packages/core/src/tools/write-file.ts
+++ b/packages/core/src/tools/write-file.ts
@@ -4,7 +4,21 @@ import { z } from "zod";
 import type { ToolDefinition } from "../types/index.js";
 import { canonicalize } from "./path-utils.js";
 
-export function createWriteFileTool(workingDirectory: string): ToolDefinition {
+/**
+ * Optional hook invoked AFTER a successful write, with the canonicalized
+ * absolute path of the file just written. Its returned string (when non-empty)
+ * is appended to the tool result. This is how LSP diagnostics are surfaced
+ * back to the model on write without coupling `@dispatch/core`'s tools to the
+ * API layer or the LSP manager — the host wires an implementation that touches
+ * the file through the LSP and formats any diagnostics. Errors thrown here are
+ * swallowed so a flaky LSP never fails the write itself.
+ */
+export type AfterWriteHook = (absolutePath: string) => Promise<string>;
+
+export function createWriteFileTool(
+	workingDirectory: string,
+	onAfterWrite?: AfterWriteHook,
+): ToolDefinition {
 	return {
 		name: "write_file",
 		description: "Write content to a file relative to the working directory.",
@@ -31,10 +45,22 @@ export function createWriteFileTool(workingDirectory: string): ToolDefinition {
 			try {
 				await mkdir(dirname(absolutePath), { recursive: true });
 				await writeFile(absolutePath, content, "utf8");
-				return `Successfully wrote to "${filePath}".`;
 			} catch (err) {
 				return `Error writing file: ${err instanceof Error ? err.message : String(err)}`;
 			}
+
+			let result = `Successfully wrote to "${filePath}".`;
+			// Post-write hook (e.g. LSP diagnostics). Best-effort: never let a
+			// hook failure turn a successful write into an error.
+			if (onAfterWrite) {
+				try {
+					const extra = await onAfterWrite(absolutePath);
+					if (extra) result += `\n\n${extra}`;
+				} catch {
+					/* ignore — diagnostics are advisory */
+				}
+			}
+			return result;
 		},
 	};
 }