feat: harden trading SDK examples

examples/middleware_system/README.md

@@ -0,0 +1,13 @@
+# Instruction Middleware
+
+[中文](README_CN.md)
+
+Demonstrates implementing `InstructionMiddleware`, installing it in a `MiddlewareManager`, and observing or modifying instructions before submission.
+
+> The example loads `PRIVATE_KEY` and calls `client.buy`. After configuration it can submit a real PumpSwap mainnet transaction.
+
+```bash
+cargo run --package middleware_system
+```
+
+Middleware must preserve signer, account-order, compute-budget, tip, nonce, and transaction-size semantics. Keep latency-sensitive middleware deterministic and free of blocking I/O.

examples/middleware_system/README_CN.md

@@ -0,0 +1,13 @@
+# 指令中间件
+
+[English](README.md)
+
+展示如何实现 `InstructionMiddleware`、安装到 `MiddlewareManager`，并在提交前观察或修改指令。
+
+> 示例从 `PRIVATE_KEY` 加载钱包并调用 `client.buy`；配置完成后可能提交真实 PumpSwap 主网交易。
+
+```bash
+cargo run --package middleware_system
+```
+
+中间件必须保持 signer、账户顺序、compute budget、tip、nonce 和交易体积语义。低延迟中间件应确定性执行，不能包含阻塞 I/O。

examples/middleware_system/src/main.rs

@@ -10,7 +10,7 @@ use sol_trade_sdk::{
     SolanaTrade, TradeTokenType,
 };
 use solana_commitment_config::CommitmentConfig;
-use solana_sdk::{instruction::Instruction, pubkey::Pubkey, signature::Keypair};
+use solana_sdk::{instruction::Instruction, pubkey::Pubkey};
 use std::{str::FromStr, sync::Arc};
 
 #[tokio::main]
@@ -59,7 +59,7 @@ impl InstructionMiddleware for CustomMiddleware {
 /// Initializes a new SolanaTrade client with configuration
 async fn create_solana_trade_client() -> AnyResult<SolanaTrade> {
     println!("🚀 Initializing SolanaTrade client...");
-    let payer = Keypair::from_base58_string("use_your_payer_keypair_here");
+    let payer = sol_trade_sdk::common::keypair::load_keypair_from_env("PRIVATE_KEY")?;
     let rpc_url = "https://api.mainnet-beta.solana.com".to_string();
     let commitment = CommitmentConfig::confirmed();
     let swqos_configs: Vec<SwqosConfig> = vec![SwqosConfig::Default(rpc_url.clone())];