fix(order-book): zero unsettled_* before token transfers in settle_funds (CEI)

settle_funds was setting market_user.unsettled_base = 0 and unsettled_quote = 0
*after* the transfer_checked CPIs. Solana CPIs are not reentrant in the
EVM sense, but checks-effects-interactions is still the right discipline:
if either transfer ever gained a path that called back into this program
(custom token hooks, transfer-fee extension with a side effect, a future
ext we don't anticipate), having the unsettled_* counters still readable
mid-transfer would let a re-entry double-withdraw the balance.

Snapshot the amounts into locals, zero the counters, then issue the
transfers. The instruction stays atomic via Solana's tx semantics \u2014 if a
transfer fails the whole tx unwinds, counters and all.

No semantic change in the success path. Tests still pass 24/24.

Author: Edward (Mike's bot)

defi/order-book/anchor/programs/order-book/src/instructions/settle_funds.rs

@@ -10,8 +10,17 @@ pub fn handle_settle_funds(context: Context<SettleFunds>) -> Result<()> {
     let market_user = &mut context.accounts.market_user;
     let market = &context.accounts.market;
 
+    // Snapshot the amounts the user is owed, then zero the counters
+    // BEFORE the token transfers. Checks-effects-interactions: even though
+    // Solana CPIs don't reenter in the EVM sense, if either transfer ever
+    // gained a path that called back into this program (custom token
+    // hooks, transfer-fee extensions with side effects, ...), having stale
+    // unsettled_* values readable mid-transfer would let a re-entry double-
+    // withdraw. Updating state first makes that class of bug impossible.
     let base_amount = market_user.unsettled_base;
     let quote_amount = market_user.unsettled_quote;
+    market_user.unsettled_base = 0;
+    market_user.unsettled_quote = 0;
 
     // Seeds to sign as the market PDA (the authority of both vaults). Built
     // once and reused for the two possible transfers.
@@ -39,7 +48,6 @@ pub fn handle_settle_funds(context: Context<SettleFunds>) -> Result<()> {
             base_amount,
             context.accounts.base_mint.decimals,
         )?;
-        market_user.unsettled_base = 0;
     }
 
     if quote_amount > 0 {
@@ -57,7 +65,6 @@ pub fn handle_settle_funds(context: Context<SettleFunds>) -> Result<()> {
             quote_amount,
             context.accounts.quote_mint.decimals,
         )?;
-        market_user.unsettled_quote = 0;
     }
 
     Ok(())