fix(pool): remove unused KLast storage key and document fee_to as reserved/inert (#108)

contracts/pool/src/lib.rs

@@ -658,6 +658,12 @@ impl NodusAmm {
 
     // ── Protocol fee collector ──────────────────────────────────────────────
 
+    /// Sets the recipient of the protocol fee.
+    /// 
+    /// # Important
+    /// Protocol fee collection is currently **not implemented** in the pool.
+    /// This is a reserved administrative endpoint; setting this value updates the configuration
+    /// but has no functional impact and no fees will accrue to the configured address.
     pub fn set_fee_to(env: Env, caller: Address, new_fee_to: Option<Address>) -> Result<(), Error> {
         require_fee_to_setter(&env, &caller)?;
         match &new_fee_to {
@@ -675,6 +681,11 @@ impl NodusAmm {
         Ok(())
     }
 
+    /// Returns the protocol fee recipient address, if configured.
+    /// 
+    /// # Important
+    /// Protocol fee collection is currently **not implemented** in the pool.
+    /// This function is non-functional/inert and is only a configuration query.
     pub fn fee_to(env: Env) -> Option<Address> {
         env.storage().instance().get(&DataKey::FeeTo)
     }

contracts/pool/src/storage.rs

@@ -12,7 +12,6 @@ pub enum DataKey {
     TimestampLast,
     Price0CumulativeLast,
     Price1CumulativeLast,
-    KLast,
     Locked,
     Initialized,
     FeeTo,

docs/ARCHITECTURE.md

@@ -19,7 +19,6 @@ These contracts communicate through cross-contract calls. The pool is the sole a
           │                                       │
           │  reserve_0 (token_0 balance)          │
           │  reserve_1 (token_1 balance)          │
-          │  k_last    (fee accumulator)          │
           │  price_X_cumulative (TWAP oracle)     │
           │                                       │
           │  add_liquidity()  ─────────────────── │──► mint LP tokens
@@ -149,7 +148,7 @@ The swap fee is 0.3% (30 basis points), implemented implicitly:
 - The output formula uses a 997/1000 multiplier on `amount_in`.
 - Fees remain in the reserves; they are not extracted to a separate address.
 - LP token holders capture fees proportionally when they burn their shares.
-- Protocol fee (if enabled) would redirect a fraction of fees to a `fee_to` address by comparing `k_last` before and after.
+- The protocol fee mechanism (which would redirect a fraction of fees to a `fee_to` address) is **not implemented**. The `fee_to` address and setter methods exist as reserved placeholders, but no protocol fees are collected or accrued.
 
 ---