docs: add documentation for FriE2F4 operation

core/src/operations/mod.rs

@@ -554,7 +554,22 @@ pub enum Operation {
     /// track of both the old and new Merkle trees.
     MrUpdate = OPCODE_MRUPDATE,
 
-    /// TODO: add docs
+    /// Performs FRI (Fast Reed-Solomon Interactive Oracle Proofs) layer folding by a factor of 4
+    /// for FRI protocol executed in a degree 2 extension of the base field.
+    ///
+    /// This operation:
+    /// - Folds 4 query values (v0, v1), (v2, v3), (v4, v5), (v6, v7) into a single value (ne0,
+    ///   ne1)
+    /// - Computes new value of the domain generator power: poe' = poe^4
+    /// - Increments layer pointer (cptr) by 2
+    /// - Checks that the previous folding was done correctly
+    /// - Shifts the stack to move an item from the overflow table to stack position 15
+    ///
+    /// Stack transition:
+    /// Input: [v7, v6, v5, v4, v3, v2, v1, v0, f_pos, d_seg, poe, pe1, pe0, a1, a0, cptr, ...]
+    /// Output: [t1, t0, s1, s0, df3, df2, df1, df0, poe^2, f_tau, cptr+2, poe^4, f_pos, ne1, ne0,
+    /// eptr, ...] where eptr is moved from the stack overflow table and is the address of the
+    /// final FRI layer.
     FriE2F4 = OPCODE_FRIE2F4,
 
     /// Performs a single step of a random linear combination defining the DEEP composition