Make use_exact_sol_amount optional with true default for PumpFun/PumpSwap

- Change use_exact_sol_amount from bool to Option<bool>
- Default to true (via unwrap_or) for PumpFun and PumpSwap DEXes
- Option is ignored for other DEXes (Raydium, Bonk, Meteora)
- Update all examples to use None (which defaults to true for applicable DEXes)
- Update README documentation

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/instruction/pumpfun.rs

@@ -118,7 +118,7 @@ impl InstructionBuilder for PumpFunInstructionBuilder {
         }
 
         let mut buy_data = [0u8; 24];
-        if params.use_exact_sol_amount {
+        if params.use_exact_sol_amount.unwrap_or(true) {
             // buy_exact_sol_in(spendable_sol_in: u64, min_tokens_out: u64)
             // Spend exactly the input SOL amount, get at least min_tokens_out
             let min_tokens_out = calculate_with_slippage_sell(

src/instruction/pumpswap.rs

@@ -187,7 +187,7 @@ impl InstructionBuilder for PumpSwapInstructionBuilder {
         // Create instruction data
         let mut data = [0u8; 24];
         if quote_is_wsol_or_usdc {
-            if params.use_exact_sol_amount {
+            if params.use_exact_sol_amount.unwrap_or(true) {
                 // buy_exact_quote_in(spendable_quote_in: u64, min_base_amount_out: u64)
                 // Spend exactly the input SOL/quote amount, get at least min_base_amount_out
                 let min_base_amount_out = crate::utils::calc::common::calculate_with_slippage_sell(

src/lib.rs

@@ -188,9 +188,10 @@ pub struct TradeBuyParams {
     /// Whether to simulate the transaction instead of executing it
     pub simulate: bool,
     /// Use exact SOL amount instructions (buy_exact_sol_in for PumpFun, buy_exact_quote_in for PumpSwap).
-    /// When true, the exact SOL/quote amount is spent and slippage is applied to output tokens.
-    /// When false (default), uses regular buy instruction where slippage is applied to SOL/quote input.
-    pub use_exact_sol_amount: bool,
+    /// When Some(true) or None (default), the exact SOL/quote amount is spent and slippage is applied to output tokens.
+    /// When Some(false), uses regular buy instruction where slippage is applied to SOL/quote input.
+    /// This option only applies to PumpFun and PumpSwap DEXes; it is ignored for other DEXes.
+    pub use_exact_sol_amount: Option<bool>,
 }
 
 /// Parameters for executing sell orders across different DEX protocols
@@ -622,7 +623,7 @@ impl TradingClient {
             fixed_output_amount: params.fixed_output_token_amount,
             gas_fee_strategy: params.gas_fee_strategy,
             simulate: params.simulate,
-            use_exact_sol_amount: false,
+            use_exact_sol_amount: None,
         };
 
         // Validate protocol params

src/trading/core/params.rs

@@ -68,9 +68,10 @@ pub struct SwapParams {
     pub gas_fee_strategy: GasFeeStrategy,
     pub simulate: bool,
     /// Use exact SOL amount instructions (buy_exact_sol_in for PumpFun, buy_exact_quote_in for PumpSwap).
-    /// When true, the exact SOL/quote amount is spent and slippage is applied to output tokens.
-    /// When false (default), uses regular buy instruction where slippage is applied to SOL/quote input.
-    pub use_exact_sol_amount: bool,
+    /// When Some(true) or None (default), the exact SOL/quote amount is spent and slippage is applied to output tokens.
+    /// When Some(false), uses regular buy instruction where slippage is applied to SOL/quote input.
+    /// This option only applies to PumpFun and PumpSwap DEXes; it is ignored for other DEXes.
+    pub use_exact_sol_amount: Option<bool>,
 }
 
 impl std::fmt::Debug for SwapParams {