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, 46 insertions, 0 deletions

diff --git a/packages/core/tests/tools/write-file.test.ts b/packages/core/tests/tools/write-file.test.ts
index f071e12..0dedbfc 100644
--- a/packages/core/tests/tools/write-file.test.ts
+++ b/packages/core/tests/tools/write-file.test.ts
@@ -103,4 +103,50 @@ describe("write_file tool", () => {
 			expect(entries).toEqual([]);
 		});
 	});
+
+	describe("onAfterWrite hook", () => {
+		it("appends the hook's returned string to a successful write", async () => {
+			const tool = createWriteFileTool(workDir, async (abs) => `DIAGNOSTICS for ${abs}`);
+			const result = await tool.execute({ path: "a.luau", content: "local x = 1" });
+			expect(result).toMatch(/successfully wrote/i);
+			expect(result).toContain("DIAGNOSTICS for");
+			expect(result).toContain(join(workDir, "a.luau"));
+		});
+
+		it("does not append when the hook returns empty string", async () => {
+			const tool = createWriteFileTool(workDir, async () => "");
+			const result = await tool.execute({ path: "a.luau", content: "local x = 1" });
+			expect(result.trim()).toMatch(/^Successfully wrote to "a\.luau"\.$/);
+		});
+
+		it("does not run the hook when the write is blocked (traversal)", async () => {
+			let called = false;
+			const tool = createWriteFileTool(workDir, async () => {
+				called = true;
+				return "should not appear";
+			});
+			const result = await tool.execute({ path: "../evil.txt", content: "bad" });
+			expect(result).toMatch(/outside the working directory/i);
+			expect(called).toBe(false);
+		});
+
+		it("swallows hook errors so a throwing hook never fails the write", async () => {
+			const tool = createWriteFileTool(workDir, async () => {
+				throw new Error("lsp blew up");
+			});
+			const result = await tool.execute({ path: "a.luau", content: "local x = 1" });
+			expect(result).toMatch(/successfully wrote/i);
+			expect(result).not.toContain("lsp blew up");
+		});
+
+		it("passes the canonical absolute path to the hook", async () => {
+			let seen = "";
+			const tool = createWriteFileTool(workDir, async (abs) => {
+				seen = abs;
+				return "";
+			});
+			await tool.execute({ path: "nested/b.luau", content: "x" });
+			expect(seen).toBe(join(workDir, "nested/b.luau"));
+		});
+	});
 });