test(lsp): cover protocol framing basics

Add LSP protocol coverage for initialize capabilities, shutdown response, and unknown request errors.

req: diagnostics/008

hemx-lsp/src/main.rs

@@ -943,6 +943,48 @@ mod tests {
         assert!(hover.to_string().contains("exercise.name: &'static str"));
     }
 
+    #[test]
+    fn lsp_protocol_initialize_shutdown_and_unknown_requests_are_framed() {
+        // req: diagnostics/008
+        let input = [
+            lsp_message(serde_json::json!({"jsonrpc": "2.0", "id": 1, "method": "initialize", "params": {}})),
+            lsp_message(serde_json::json!({"jsonrpc": "2.0", "id": 2, "method": "hemx/unknown", "params": {}})),
+            lsp_message(serde_json::json!({"jsonrpc": "2.0", "id": 3, "method": "shutdown", "params": null})),
+            lsp_message(serde_json::json!({"jsonrpc": "2.0", "method": "exit"})),
+        ]
+        .join("");
+        let mut reader = std::io::BufReader::new(input.as_bytes());
+        let mut output = Vec::new();
+
+        serve_lsp(&mut reader, &mut output).expect("serve LSP");
+        let messages = lsp_messages(&output);
+        assert_eq!(
+            messages.len(),
+            3,
+            "initialize, unknown request, shutdown responses"
+        );
+        assert_eq!(messages[0]["id"], 1);
+        assert_eq!(
+            messages[0]["result"]["capabilities"]["textDocumentSync"]["openClose"],
+            true
+        );
+        assert_eq!(
+            messages[0]["result"]["capabilities"]["completionProvider"]["triggerCharacters"][0],
+            "h"
+        );
+        assert_eq!(messages[0]["result"]["capabilities"]["hoverProvider"], true);
+        assert_eq!(messages[1]["id"], 2);
+        assert_eq!(messages[1]["error"]["code"], -32601);
+        assert!(messages[1]["error"]["message"]
+            .as_str()
+            .unwrap_or_default()
+            .contains("hemx/unknown"));
+        assert_eq!(
+            messages[2],
+            serde_json::json!({"jsonrpc": "2.0", "id": 3, "result": null})
+        );
+    }
+
     #[test]
     fn lsp_publishes_and_clears_build_equivalent_diagnostics() {
         // req: diagnostics/004 req: diagnostics/005