fix(lsp): replied to defined server requests with spec no-ops

handleServerRequest fell through to a JSON-RPC -32601 Method not found for several defined server -> client requests (window/showMessageRequest, window/showDocument, workspace/{semanticTokens,inlayHint,codeLens,codeAction,diagnostic}/refresh). Servers that block on a real reply -- the same failure class as the client/registerCapability hang fixed in #3029 -- could stall waiting for an acknowledgement that never came.

Reply with the spec no-op result instead: null for showMessageRequest / *Refresh, { success: false } for showDocument. Headless omp cannot honour the UI surface, but it still owes a defined response.

Fixes #3044

packages/coding-agent/CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+### Fixed
+
+- Fixed LSP client returning `-32601 Method not found` for defined server→client requests (`window/showMessageRequest`, `window/showDocument`, `workspace/{semanticTokens,inlayHint,codeLens,codeAction,diagnostic}/refresh`). Servers that stall waiting for a real reply (same failure mode as #3029) now receive the spec no-op result ([#3044](https://github.com/can1357/oh-my-pi/issues/3044)).
+
 ## [16.1.1] - 2026-06-19
 
 ### Changed

packages/coding-agent/src/lsp/client.ts

@@ -482,6 +482,28 @@ async function handleServerRequest(client: LspClient, message: LspJsonRpcRequest
 		await sendResponse(client, message.id, null, message.method);
 		return;
 	}
+	if (message.method === "window/showMessageRequest") {
+		// Headless: no UI to surface the prompt. Spec says null = "no action selected".
+		await sendResponse(client, message.id, null, message.method);
+		return;
+	}
+	if (message.method === "window/showDocument") {
+		// Headless: nothing to display. Spec result is `{ success: boolean }`.
+		await sendResponse(client, message.id, { success: false }, message.method);
+		return;
+	}
+	if (
+		message.method === "workspace/semanticTokens/refresh" ||
+		message.method === "workspace/inlayHint/refresh" ||
+		message.method === "workspace/codeLens/refresh" ||
+		message.method === "workspace/codeAction/refresh" ||
+		message.method === "workspace/diagnostic/refresh"
+	) {
+		// Void acknowledgement per spec; servers that stall waiting for a reply
+		// (same failure mode as the dynamic-registration hang in #3029) move on.
+		await sendResponse(client, message.id, null, message.method);
+		return;
+	}
 	await sendResponse(client, message.id, null, message.method, {
 		code: -32601,
 		message: `Method not found: ${message.method}`,

packages/coding-agent/test/tools/lsp-regressions.test.ts

@@ -380,6 +380,67 @@ describe("lsp regressions", () => {
 		}
 	});
 
+	it("answers defined server→client requests with spec no-op results", async () => {
+		// Same failure class as #3029: a defined server→client request
+		// (window/showMessage{Request}, window/showDocument, workspace/*/refresh)
+		// must receive a spec-shaped reply, not a -32601. Headless omp can't
+		// surface UI prompts but still owes a defined no-op.
+		const tempDir = TempDir.createSync("@omp-lsp-server-requests-");
+		try {
+			const server = installFakeLsp((message, srv) => {
+				if (message.method === "initialize") {
+					srv.send({ jsonrpc: "2.0", id: message.id, result: { capabilities: {} } });
+				} else if (message.method === "initialized") {
+					srv.send({
+						jsonrpc: "2.0",
+						id: 9101,
+						method: "window/showMessageRequest",
+						params: { type: 1, message: "x", actions: [{ title: "Cancel" }] },
+					});
+					srv.send({
+						jsonrpc: "2.0",
+						id: 9102,
+						method: "window/showDocument",
+						params: { uri: "file:///tmp/a.md" },
+					});
+					srv.send({ jsonrpc: "2.0", id: 9103, method: "workspace/semanticTokens/refresh" });
+					srv.send({ jsonrpc: "2.0", id: 9104, method: "workspace/inlayHint/refresh" });
+					srv.send({ jsonrpc: "2.0", id: 9105, method: "workspace/codeLens/refresh" });
+					srv.send({ jsonrpc: "2.0", id: 9106, method: "workspace/diagnostic/refresh" });
+				} else if (message.method === "shutdown") {
+					srv.send({ jsonrpc: "2.0", id: message.id, result: null });
+				} else if (message.method === "exit") {
+					srv.exit(0);
+				}
+			});
+
+			const config: ServerConfig = {
+				command: "fake-lsp",
+				fileTypes: ["rs"],
+				rootMarkers: [],
+			};
+
+			await lspClient.getOrCreateClient(config, tempDir.path(), 1_000);
+
+			const showMessage = await server.waitFor(message => message.id === 9101 && message.method === undefined);
+			expect(showMessage.error).toBeUndefined();
+			expect(showMessage.result).toBeNull();
+
+			const showDocument = await server.waitFor(message => message.id === 9102 && message.method === undefined);
+			expect(showDocument.error).toBeUndefined();
+			expect(showDocument.result).toEqual({ success: false });
+
+			for (const id of [9103, 9104, 9105, 9106]) {
+				const refresh = await server.waitFor(message => message.id === id && message.method === undefined);
+				expect(refresh.error).toBeUndefined();
+				expect(refresh.result).toBeNull();
+			}
+		} finally {
+			await lspClient.shutdownAll();
+			tempDir.removeSync();
+		}
+	});
+
 	it("opens rust-analyzer Cargo workspace files before polling workspace readiness", async () => {
 		const tempDir = TempDir.createSync("@omp-lsp-rust-workspace-");
 		try {