fix: eliminate command injection and unhandled JSON.parse in LSP tool

- config.ts: Replace execSync(`which ${command}`) with spawnSync("which", [command])
  to prevent shell injection from malicious lsp.json config files
- client.ts: Wrap JSON.parse in parseMessage with try/catch and handle null messages
  in the stream reader to prevent process crashes from malformed LSP output

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

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

@@ -164,7 +164,7 @@ const CLIENT_CAPABILITIES = {
 
 function parseMessage(
 	buffer: Buffer,
-): { message: LspJsonRpcResponse | LspJsonRpcNotification; remaining: Buffer } | null {
+): { message: LspJsonRpcResponse | LspJsonRpcNotification | null; remaining: Buffer } | null {
 	const headerEndIndex = findHeaderEnd(buffer);
 	if (headerEndIndex === -1) return null;
 
@@ -182,10 +182,15 @@ function parseMessage(
 	const messageText = new TextDecoder().decode(messageBytes);
 	const remaining = Buffer.from(buffer.subarray(messageEnd));
 
-	return {
-		message: JSON.parse(messageText),
-		remaining,
-	};
+	let message: LspJsonRpcResponse | LspJsonRpcNotification;
+	try {
+		message = JSON.parse(messageText);
+	} catch {
+		// Malformed JSON from LSP server — skip this message and advance past it
+		return { message: null, remaining };
+	}
+
+	return { message, remaining };
 }
 
 function findHeaderEnd(buffer: Uint8Array): number {
@@ -239,6 +244,11 @@ async function startMessageReader(client: LspClient): Promise<void> {
 				const { message, remaining } = parsed;
 				workingBuffer = remaining;
 
+				if (!message) {
+					parsed = parseMessage(workingBuffer);
+					continue;
+				}
+
 				if ("id" in message && message.id !== undefined) {
 					const pending = client.pendingRequests.get(message.id);
 					if (pending) {

packages/pi-coding-agent/src/core/lsp/config.ts

@@ -2,7 +2,7 @@ import * as fs from "node:fs";
 import { createRequire } from "node:module";
 import * as os from "node:os";
 import * as path from "node:path";
-import { execSync } from "node:child_process";
+import { spawnSync } from "node:child_process";
 import YAML from "yaml";
 import { globSync } from "glob";
 import { CONFIG_DIR_NAME } from "../../config.js";
@@ -177,11 +177,9 @@ const LOCAL_BIN_PATHS: Array<{ markers: string[]; binDir: string }> = [
 ];
 
 function which(command: string): string | null {
-	try {
-		return execSync(`which ${command}`, { encoding: "utf-8" }).trim() || null;
-	} catch {
-		return null;
-	}
+	const result = spawnSync("which", [command], { encoding: "utf-8" });
+	if (result.status !== 0) return null;
+	return result.stdout.trim() || null;
 }
 
 export function resolveCommand(command: string, cwd: string): string | null {