diff --git a/.github/workflows/contract-fuzz.yml b/.github/workflows/contract-fuzz.yml
new file mode 100644
index 0000000..a0bf6ca
--- /dev/null
+++ b/.github/workflows/contract-fuzz.yml
@@ -0,0 +1,31 @@
+name: Contract Fuzz Smoke Tests
+
+on:
+  pull_request:
+    branches: [main]
+    paths:
+      - 'contracts/vault/**'
+      - 'contracts/streaming/**'
+      - 'fuzz/**'
+      - '.github/workflows/contract-fuzz.yml'
+  push:
+    branches: [main, 'agent/**', 'feat/**']
+    paths:
+      - 'contracts/vault/**'
+      - 'contracts/streaming/**'
+      - 'fuzz/**'
+      - '.github/workflows/contract-fuzz.yml'
+  workflow_dispatch:
+
+jobs:
+  fuzz:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v5
+      - uses: dtolnay/rust-toolchain@nightly
+      - name: Install cargo-fuzz
+        run: cargo install cargo-fuzz --locked
+      - name: Fuzz vault deposit math
+        run: cargo fuzz run vault_deposit -- -runs=10000
+      - name: Fuzz stream release math
+        run: cargo fuzz run stream_release -- -runs=10000
\ No newline at end of file
diff --git a/Cargo.lock b/Cargo.lock
index fcf9c60..f398411 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1693,6 +1693,7 @@ name = "soromint-streaming"
 version = "0.1.0"
 dependencies = [
  "soroban-sdk",
+ "soromint-token",
 ]
 
 [[package]]
@@ -1710,6 +1711,7 @@ version = "0.1.0"
 dependencies = [
  "proptest",
  "soroban-sdk",
+ "soromint-access",
  "soromint-lifecycle",
 ]
 
diff --git a/contracts/streaming/Cargo.toml b/contracts/streaming/Cargo.toml
index 1187fc0..0c9cb49 100644
--- a/contracts/streaming/Cargo.toml
+++ b/contracts/streaming/Cargo.toml
@@ -13,3 +13,4 @@ soroban-sdk = "22.0.0"
 [dev-dependencies]
 soroban-sdk = { version = "22.0.0", features = ["testutils"] }
 soromint-token = { path = "../token" }
+proptest = "1.6"
diff --git a/contracts/streaming/src/lib.rs b/contracts/streaming/src/lib.rs
index f81d2e5..e695b84 100644
--- a/contracts/streaming/src/lib.rs
+++ b/contracts/streaming/src/lib.rs
@@ -4,6 +4,7 @@
 //! Supports real-time payroll, subscription payments, and milestone-based vesting.
 
 #![no_std]
+pub mod math;
 
 use soroban_sdk::{contract, contractimpl, contracttype, token, Address, Env, Bytes, IntoVal, Symbol, symbol_short};
 
@@ -391,7 +392,7 @@ impl StreamingPayments {
 
     fn calculate_streamed(e: &Env, stream: &Stream, schedule: &Schedule) -> i128 {
         match schedule {
-            Schedule::Linear(_) => Self::calculate_linear_streamed(e, stream),
+            Schedule::Linear(total_amount) => math::vested_amount(*total_amount, stream.start_ledger, stream.stop_ledger, e.ledger().sequence()).expect("stream release overflow"),
             Schedule::Milestone(milestones) => {
                 let current = e.ledger().sequence();
                 let mut streamed = 0i128;
diff --git a/contracts/streaming/src/math.rs b/contracts/streaming/src/math.rs
new file mode 100644
index 0000000..847ed7b
--- /dev/null
+++ b/contracts/streaming/src/math.rs
@@ -0,0 +1,53 @@
+//! Overflow-safe release schedule arithmetic.
+
+pub fn vested_amount(
+    total_amount: i128,
+    start_ledger: u32,
+    stop_ledger: u32,
+    current_ledger: u32,
+) -> Option<i128> {
+    if total_amount < 0 || stop_ledger <= start_ledger {
+        return None;
+    }
+    if current_ledger <= start_ledger {
+        return Some(0);
+    }
+    if current_ledger >= stop_ledger {
+        return Some(total_amount);
+    }
+
+    let elapsed = i128::from(current_ledger - start_ledger);
+    let duration = i128::from(stop_ledger - start_ledger);
+    total_amount.checked_mul(elapsed)?.checked_div(duration)
+}
+
+#[cfg(test)]
+mod property_tests {
+    use super::*;
+    use proptest::prelude::*;
+
+    proptest! {
+        #[test]
+        fn release_is_bounded_and_complete(total in 0i128..=1_000_000_000_000_000, start in 0u32..=1_000_000, duration in 1u32..=1_000_000) {
+            let stop = start + duration;
+            prop_assert_eq!(vested_amount(total, start, stop, start), Some(0));
+            prop_assert_eq!(vested_amount(total, start, stop, stop), Some(total));
+            let vested = vested_amount(total, start, stop, start + duration / 2).unwrap();
+            prop_assert!((0..=total).contains(&vested));
+        }
+
+        #[test]
+        fn release_is_monotonic(total in 0i128..=1_000_000_000_000_000, start in 0u32..=1_000_000, duration in 1u32..=1_000_000, first in 0u32..=1_000_000, second in 0u32..=1_000_000) {
+            let stop = start + duration;
+            let a = start + first.min(duration);
+            let b = start + second.min(duration);
+            let (earlier, later) = if a <= b { (a, b) } else { (b, a) };
+            prop_assert!(vested_amount(total, start, stop, later).unwrap() >= vested_amount(total, start, stop, earlier).unwrap());
+        }
+
+        #[test]
+        fn indivisible_totals_release_fully(total in 1i128..=1_000_000_000_000_000, duration in 1u32..=1_000_000) {
+            prop_assert_eq!(vested_amount(total, 0, duration, duration), Some(total));
+        }
+    }
+}
diff --git a/contracts/vault/Cargo.toml b/contracts/vault/Cargo.toml
index 787a2d7..ea815d0 100644
--- a/contracts/vault/Cargo.toml
+++ b/contracts/vault/Cargo.toml
@@ -12,6 +12,7 @@ soroban-sdk = "22.0.0"
 
 [dev-dependencies]
 soroban-sdk = { version = "22.0.0", features = ["testutils"] }
+proptest = "1.6"
 
 [profile.release]
 opt-level = "z"
diff --git a/contracts/vault/src/lib.rs b/contracts/vault/src/lib.rs
index 41b8d0a..0f4cf9a 100644
--- a/contracts/vault/src/lib.rs
+++ b/contracts/vault/src/lib.rs
@@ -5,6 +5,7 @@ mod oracle;
 mod liquidation;
 mod events;
 mod reentrancy;
+pub mod math;
 
 #[cfg(test)]
 mod test;
@@ -109,11 +110,11 @@ impl VaultContract {
         let smt_price = 1_0000000i128; // SMT pegged to $1 with 7 decimals
 
         // Calculate collateral value in USD
-        let collateral_value = (collateral_amount * collateral_price) / 1_0000000;
+        let collateral_value = math::collateral_value(collateral_amount, collateral_price, 1_0000000).expect("collateral value overflow");
         let debt_value = (smt_amount * smt_price) / 1_0000000;
 
         // Check collateralization ratio
-        let ratio = (collateral_value * BP_DIVISOR as i128) / debt_value;
+        let ratio = math::collateralization_ratio(collateral_value, debt_value, BP_DIVISOR as i128).expect("collateral ratio overflow");
         if ratio < config.min_collateral_ratio as i128 {
             panic!("insufficient collateral ratio");
         }
@@ -436,7 +437,7 @@ impl VaultContract {
         let smt_price = 1_0000000i128;
         let debt_value = (debt * smt_price) / 1_0000000;
 
-        let ratio = (collateral_value * BP_DIVISOR as i128) / debt_value;
+        let ratio = math::collateralization_ratio(collateral_value, debt_value, BP_DIVISOR as i128).expect("collateral ratio overflow");
 
         // Check against the strictest min collateral ratio
         let mut min_ratio = MIN_COLLATERAL_RATIO;
@@ -462,7 +463,7 @@ impl VaultContract {
         let smt_price = 1_0000000i128;
         let debt_value = (position.debt * smt_price) / 1_0000000;
 
-        let ratio = (collateral_value * BP_DIVISOR as i128) / debt_value;
+        let ratio = math::collateralization_ratio(collateral_value, debt_value, BP_DIVISOR as i128).expect("collateral ratio overflow");
 
         // Check against the highest liquidation threshold
         let mut threshold = LIQUIDATION_THRESHOLD;
diff --git a/contracts/vault/src/math.rs b/contracts/vault/src/math.rs
new file mode 100644
index 0000000..6a7c132
--- /dev/null
+++ b/contracts/vault/src/math.rs
@@ -0,0 +1,50 @@
+//! Checked arithmetic used by vault valuation and fuzz/property tests.
+
+pub fn collateral_value(amount: i128, price: i128, scale: i128) -> Option<i128> {
+    if amount < 0 || price < 0 || scale <= 0 {
+        return None;
+    }
+    amount.checked_mul(price)?.checked_div(scale)
+}
+
+pub fn collateralization_ratio(
+    collateral_value: i128,
+    debt_value: i128,
+    basis_points: i128,
+) -> Option<i128> {
+    if collateral_value < 0 || debt_value <= 0 || basis_points <= 0 {
+        return None;
+    }
+    collateral_value
+        .checked_mul(basis_points)?
+        .checked_div(debt_value)
+}
+
+#[cfg(test)]
+mod property_tests {
+    use super::*;
+    use proptest::prelude::*;
+
+    proptest! {
+        #[test]
+        fn valuation_matches_checked_reference(amount in 0i128..=1_000_000_000_000_000, price in 0i128..=1_000_000_000_000, scale in 1i128..=1_000_000_000) {
+            let expected = amount.checked_mul(price).and_then(|v| v.checked_div(scale));
+            prop_assert_eq!(collateral_value(amount, price, scale), expected);
+        }
+
+        #[test]
+        fn valuation_is_monotonic(smaller in 0i128..=1_000_000_000_000, delta in 0i128..=1_000_000_000_000, price in 1i128..=1_000_000_000, scale in 1i128..=100_000_000) {
+            if let Some(larger) = smaller.checked_add(delta) {
+                let low = collateral_value(smaller, price, scale).unwrap();
+                let high = collateral_value(larger, price, scale).unwrap();
+                prop_assert!(high >= low);
+            }
+        }
+
+        #[test]
+        fn ratio_matches_checked_reference(collateral in 0i128..=1_000_000_000_000_000, debt in 1i128..=1_000_000_000_000) {
+            let expected = collateral.checked_mul(10_000).and_then(|v| v.checked_div(debt));
+            prop_assert_eq!(collateralization_ratio(collateral, debt, 10_000), expected);
+        }
+    }
+}
diff --git a/fuzz/.gitignore b/fuzz/.gitignore
new file mode 100644
index 0000000..ca3697f
--- /dev/null
+++ b/fuzz/.gitignore
@@ -0,0 +1,4 @@
+artifacts/
+corpus/
+coverage/
+target/
\ No newline at end of file
diff --git a/fuzz/Cargo.toml b/fuzz/Cargo.toml
new file mode 100644
index 0000000..04a68db
--- /dev/null
+++ b/fuzz/Cargo.toml
@@ -0,0 +1,28 @@
+[package]
+name = "soromint-fuzz"
+version = "0.0.0"
+edition = "2021"
+publish = false
+
+[package.metadata]
+cargo-fuzz = true
+
+[dependencies]
+libfuzzer-sys = "0.4"
+
+[[bin]]
+name = "vault_deposit"
+path = "fuzz_targets/vault_deposit.rs"
+test = false
+doc = false
+bench = false
+
+[[bin]]
+name = "stream_release"
+path = "fuzz_targets/stream_release.rs"
+test = false
+doc = false
+bench = false
+
+[workspace]
+members = ["."]
\ No newline at end of file
diff --git a/fuzz/README.md b/fuzz/README.md
new file mode 100644
index 0000000..b3ec2af
--- /dev/null
+++ b/fuzz/README.md
@@ -0,0 +1,11 @@
+# Contract fuzz targets
+
+Install cargo-fuzz, then run each target from the repository root:
+
+```bash
+cargo install cargo-fuzz
+cargo fuzz run vault_deposit -- -max_total_time=60
+cargo fuzz run stream_release -- -max_total_time=60
+```
+
+Both targets exercise the same checked arithmetic used by the contracts.
\ No newline at end of file
diff --git a/fuzz/fuzz_targets/stream_release.rs b/fuzz/fuzz_targets/stream_release.rs
new file mode 100644
index 0000000..ffbc3bc
--- /dev/null
+++ b/fuzz/fuzz_targets/stream_release.rs
@@ -0,0 +1,33 @@
+#![no_main]
+use libfuzzer_sys::fuzz_target;
+#[path = "../../contracts/streaming/src/math.rs"]
+mod stream_math;
+
+fuzz_target!(|data: &[u8]| {
+    if data.len() < 28 {
+        return;
+    }
+    let total = i128::from_le_bytes(data[0..16].try_into().unwrap()).saturating_abs();
+    let start = u32::from_le_bytes(data[16..20].try_into().unwrap());
+    let duration = u32::from_le_bytes(data[20..24].try_into().unwrap()).max(1);
+    let offset = u32::from_le_bytes(data[24..28].try_into().unwrap());
+    let Some(stop) = start.checked_add(duration) else {
+        return;
+    };
+    let current = start.saturating_add(offset.min(duration));
+    let Some(vested) = stream_math::vested_amount(total, start, stop, current) else {
+        // Checked arithmetic deliberately rejects schedules whose intermediate
+        // multiplication cannot be represented.
+        return;
+    };
+    assert!((0..=total).contains(&vested));
+    assert_eq!(
+        stream_math::vested_amount(total, start, stop, stop),
+        Some(total)
+    );
+    if current < stop {
+        if let Some(next) = stream_math::vested_amount(total, start, stop, current + 1) {
+            assert!(next >= vested);
+        }
+    }
+});
diff --git a/fuzz/fuzz_targets/vault_deposit.rs b/fuzz/fuzz_targets/vault_deposit.rs
new file mode 100644
index 0000000..43d7e3f
--- /dev/null
+++ b/fuzz/fuzz_targets/vault_deposit.rs
@@ -0,0 +1,21 @@
+#![no_main]
+use libfuzzer_sys::fuzz_target;
+#[path = "../../contracts/vault/src/math.rs"]
+mod vault_math;
+
+fuzz_target!(|data: &[u8]| {
+    if data.len() < 48 {
+        return;
+    }
+    let amount = i128::from_le_bytes(data[0..16].try_into().unwrap()).saturating_abs();
+    let price = i128::from_le_bytes(data[16..32].try_into().unwrap()).saturating_abs();
+    let debt = i128::from_le_bytes(data[32..48].try_into().unwrap()).saturating_abs();
+    if let Some(value) = vault_math::collateral_value(amount, price, 10_000_000) {
+        assert!(value >= 0);
+        if debt > 0 {
+            if let Some(ratio) = vault_math::collateralization_ratio(value, debt, 10_000) {
+                assert!(ratio >= 0);
+            }
+        }
+    }
+});