diff --git a/executor/src/lib.rs b/executor/src/lib.rs
index 419e4ac4..104a9f93 100644
--- a/executor/src/lib.rs
+++ b/executor/src/lib.rs
@@ -393,6 +393,7 @@ pub async fn run_with_impl(
             topmost_runner_id,
         },
     };
+    let message_fee_cascade = entry_data.message_fee_cascade;
     let message_fee_allocation = entry_data
         .message_fee_allocation
         .into_iter()
@@ -434,7 +435,11 @@ pub async fn run_with_impl(
         det_subvm_hashes: Default::default(),
     });
 
-    let run_result = rt::spawn_apply_run(&supervisor, essential_data).await?;
+    let mut run_result = rt::spawn_apply_run(&supervisor, essential_data).await?;
+
+    if let Some(cascade) = &message_fee_cascade {
+        rt::cascade::apply(&mut run_result.vm_data.accumulator.emissions, cascade);
+    }
 
     Ok(rt::vm::FullResult {
         kind: match &run_result.run_ok {
diff --git a/executor/src/rt/cascade.rs b/executor/src/rt/cascade.rs
new file mode 100644
index 00000000..cae3ad78
--- /dev/null
+++ b/executor/src/rt/cascade.rs
@@ -0,0 +1,46 @@
+use primitive_types::U256;
+
+use crate::domain::ExecutionEmission;
+
+fn internal_fee(emission: &mut ExecutionEmission) -> Option<&mut U256> {
+    match emission {
+        ExecutionEmission::PostMessage { message_fee, .. }
+        | ExecutionEmission::DeployContract { message_fee, .. } => Some(message_fee),
+        _ => None,
+    }
+}
+
+/// Raises each internal message to the floor, then adds an equal share of half
+/// of `budget_total - Σ fees`; the other half stays with the parent so one deep
+/// path cannot drain the tree
+pub fn apply(
+    emissions: &mut [ExecutionEmission],
+    cascade: &genvm_modules_interfaces::fees::MessageFeeCascade,
+) {
+    let mut sum = U256::zero();
+    let mut count = 0u64;
+
+    for fee in emissions.iter_mut().filter_map(internal_fee) {
+        *fee = (*fee).max(cascade.min_primary_fee);
+        sum = sum.saturating_add(*fee);
+        count += 1;
+    }
+
+    if count == 0 || sum >= cascade.budget_total {
+        return;
+    }
+
+    let per_child = (cascade.budget_total - sum) / (U256::from(2) * U256::from(count));
+    if per_child.is_zero() {
+        return;
+    }
+
+    // Each fee is at most `sum`, and `per_child` at most `budget_total - sum`
+    for fee in emissions.iter_mut().filter_map(internal_fee) {
+        *fee += per_child;
+    }
+}
+
+#[cfg(test)]
+#[path = "cascade_test.rs"]
+mod tests;
diff --git a/executor/src/rt/cascade_test.rs b/executor/src/rt/cascade_test.rs
new file mode 100644
index 00000000..9e5492f7
--- /dev/null
+++ b/executor/src/rt/cascade_test.rs
@@ -0,0 +1,85 @@
+use super::*;
+use crate::domain::fees;
+
+fn params() -> fees::InternalMessageParams {
+    fees::InternalMessageParams {
+        leader_timeunits_allocation: U256::one(),
+        validator_timeunits_allocation: U256::one(),
+        execution_budget_per_round: U256::one(),
+        rotations: vec![U256::one()],
+        max_price_gen_per_time_unit: U256::one(),
+        storage_fee_max_gas_price: U256::one(),
+        receipt_fee_max_gas_price: U256::one(),
+    }
+}
+
+fn post(message_fee: u64) -> ExecutionEmission {
+    ExecutionEmission::PostMessage {
+        call_key: genlayer_sdk::abi::CallKey([0; 32]),
+        address: genlayer_sdk::calldata::Address::zero(),
+        calldata: genlayer_calldata::codec::Maybe::Materialized(
+            genlayer_sdk::calldata::Value::Null,
+        ),
+        value: U256::zero(),
+        on: genlayer_sdk::abi::gl_call::On::Finalized,
+        message_fee: U256::from(message_fee),
+        receipt_fee: U256::zero(),
+        fee_params: params(),
+        subtree: bytes::Bytes::new(),
+    }
+}
+
+fn deploy(message_fee: u64) -> ExecutionEmission {
+    ExecutionEmission::DeployContract {
+        calldata: genlayer_calldata::codec::Maybe::Materialized(
+            genlayer_sdk::calldata::Value::Null,
+        ),
+        code: bytes::Bytes::new(),
+        value: U256::zero(),
+        on: genlayer_sdk::abi::gl_call::On::Finalized,
+        salt_nonce: U256::zero(),
+        message_fee: U256::from(message_fee),
+        receipt_fee: U256::zero(),
+        fee_params: params(),
+        subtree: bytes::Bytes::new(),
+    }
+}
+
+fn fees_of(emissions: &[ExecutionEmission]) -> Vec<u64> {
+    emissions
+        .iter()
+        .map(|e| match e {
+            ExecutionEmission::PostMessage { message_fee, .. }
+            | ExecutionEmission::DeployContract { message_fee, .. }
+            | ExecutionEmission::EthSend { message_fee, .. } => message_fee.low_u64(),
+            ExecutionEmission::EmitEvent { .. } => 0,
+        })
+        .collect()
+}
+
+#[test]
+fn floors_then_splits_half_of_spare_across_posts_and_deploys() {
+    let mut emissions = vec![post(10), deploy(40)];
+    apply(
+        &mut emissions,
+        &genvm_modules_interfaces::fees::MessageFeeCascade {
+            min_primary_fee: U256::from(30),
+            budget_total: U256::from(1_000),
+        },
+    );
+    // floors 30 + 40 = 70, spare 930, per child 930 / 4 = 232
+    assert_eq!(fees_of(&emissions), vec![262, 272]);
+}
+
+#[test]
+fn no_spare_only_floors() {
+    let mut emissions = vec![post(10), post(10)];
+    apply(
+        &mut emissions,
+        &genvm_modules_interfaces::fees::MessageFeeCascade {
+            min_primary_fee: U256::from(30),
+            budget_total: U256::from(60),
+        },
+    );
+    assert_eq!(fees_of(&emissions), vec![30, 30]);
+}
diff --git a/executor/src/rt/mod.rs b/executor/src/rt/mod.rs
index 7b8f1db1..fb8aae66 100644
--- a/executor/src/rt/mod.rs
+++ b/executor/src/rt/mod.rs
@@ -1,3 +1,4 @@
+pub mod cascade;
 pub mod errors;
 pub mod fees;
 pub mod memlimiter;