diff --git a/.github/workflows/soroban_fuzz.yml b/.github/workflows/soroban_fuzz.yml
new file mode 100644
index 00000000..2f65ceff
--- /dev/null
+++ b/.github/workflows/soroban_fuzz.yml
@@ -0,0 +1,226 @@
+name: Soroban Fuzz (Smoke — 60 s per target)
+
+on:
+  push:
+    branches: [main]
+    paths:
+      - 'quantara/soroban/contracts/*/fuzz/**'
+      - '.github/workflows/soroban_fuzz.yml'
+  pull_request:
+    branches: [main]
+    paths:
+      - 'quantara/soroban/contracts/*/fuzz/**'
+      - '.github/workflows/soroban_fuzz.yml'
+  workflow_dispatch:
+    inputs:
+      fuzz_time:
+        description: 'Seconds to fuzz per target'
+        default: '60'
+        required: false
+
+env:
+  CARGO_TERM_COLOR: always
+  FUZZ_TIME: ${{ github.event.inputs.fuzz_time || '60' }}
+
+jobs:
+  # ── Vault fuzz targets ────────────────────────────────────────────────────
+  fuzz-vault:
+    name: Fuzz vault (${{ matrix.target }})
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        target:
+          - fuzz_vault_deposit
+          - fuzz_vault_withdraw
+
+    defaults:
+      run:
+        working-directory: quantara/soroban/contracts/vault
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Install latest Rust nightly
+        uses: dtolnay/rust-toolchain@nightly
+
+      - name: Cache Cargo registry
+        uses: actions/cache@v4
+        with:
+          path: |
+            ~/.cargo/registry/index/
+            ~/.cargo/registry/cache/
+            ~/.cargo/git/db/
+          key: ${{ runner.os }}-cargo-fuzz-${{ github.sha }}
+          restore-keys: ${{ runner.os }}-cargo-fuzz-
+
+      - name: Install cargo-fuzz
+        run: cargo install cargo-fuzz
+
+      - name: Pin ed25519-dalek and rand_core to 0.6 family
+        # soroban-env-host 22.1.3's testutils.rs passes `ChaCha20Rng` into
+        # `ed25519_dalek::SigningKey::generate`, which requires CryptoRng
+        # from the rand_core 0.6 family. ed25519-dalek 3.x bumped to
+        # rand_core 0.10, breaking the trait bound. Pin ed25519-dalek to
+        # 2.1.1 (last 2.x release) and rand_core to 0.6.4; fall through
+        # with `|| true` for compatibility — cargo refuses to demote a
+        # rand_core 0.10 instance to 0.6.4 directly, but the ed25519-dalek
+        # pin upstream of it is the real lever.
+        # The fuzz crate is an isolated workspace ([workspace] in
+        # fuzz/Cargo.toml), so it has its OWN fuzz/Cargo.lock. Without
+        # `cd fuzz`, `cargo update` would mutate the parent contract
+        # workspace's lockfile, which `cargo fuzz run` ignores — hence
+        # the silent failure of the previous (no-cd) variant.
+        run: |
+          cd fuzz
+          cargo update -p ed25519-dalek@3.0.0 --precise 2.1.1 || true
+          cargo update -p ed25519-dalek --precise 2.1.1 || true
+          cargo update -p rand_core@0.10.1 --precise 0.6.4 || true
+          cargo update -p rand_core@0.9.5  --precise 0.6.4 || true
+
+      - name: Run fuzz target for ${{ env.FUZZ_TIME }}s
+        run: |
+          cargo fuzz run ${{ matrix.target }} \
+            -- -max_total_time=${{ env.FUZZ_TIME }} -jobs=1
+
+      - name: Upload crash corpus on failure
+        if: failure()
+        uses: actions/upload-artifact@v4
+        with:
+          name: vault-${{ matrix.target }}-crash-corpus
+          path: fuzz/corpus/${{ matrix.target }}
+          if-no-files-found: ignore
+
+  # ── Looping fuzz targets ───────────────────────────────────────────────────
+  fuzz-looping:
+    name: Fuzz looping (${{ matrix.target }})
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        target:
+          - fuzz_looping_open_position
+
+    defaults:
+      run:
+        working-directory: quantara/soroban/contracts/looping
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Install latest Rust nightly
+        uses: dtolnay/rust-toolchain@nightly
+
+      - name: Cache Cargo registry
+        uses: actions/cache@v4
+        with:
+          path: |
+            ~/.cargo/registry/index/
+            ~/.cargo/registry/cache/
+            ~/.cargo/git/db/
+          key: ${{ runner.os }}-cargo-fuzz-${{ github.sha }}
+          restore-keys: ${{ runner.os }}-cargo-fuzz-
+
+      - name: Install cargo-fuzz
+        run: cargo install cargo-fuzz
+
+      - name: Pin ed25519-dalek and rand_core to 0.6 family
+        # soroban-env-host 22.1.3's testutils.rs passes `ChaCha20Rng` into
+        # `ed25519_dalek::SigningKey::generate`, which requires CryptoRng
+        # from the rand_core 0.6 family. ed25519-dalek 3.x bumped to
+        # rand_core 0.10, breaking the trait bound. Pin ed25519-dalek to
+        # 2.1.1 (last 2.x release) and rand_core to 0.6.4; fall through
+        # with `|| true` for compatibility — cargo refuses to demote a
+        # rand_core 0.10 instance to 0.6.4 directly, but the ed25519-dalek
+        # pin upstream of it is the real lever.
+        # The fuzz crate is an isolated workspace ([workspace] in
+        # fuzz/Cargo.toml), so it has its OWN fuzz/Cargo.lock. Without
+        # `cd fuzz`, `cargo update` would mutate the parent contract
+        # workspace's lockfile, which `cargo fuzz run` ignores — hence
+        # the silent failure of the previous (no-cd) variant.
+        run: |
+          cd fuzz
+          cargo update -p ed25519-dalek@3.0.0 --precise 2.1.1 || true
+          cargo update -p ed25519-dalek --precise 2.1.1 || true
+          cargo update -p rand_core@0.10.1 --precise 0.6.4 || true
+          cargo update -p rand_core@0.9.5  --precise 0.6.4 || true
+
+      - name: Run fuzz target for ${{ env.FUZZ_TIME }}s
+        run: |
+          cargo fuzz run ${{ matrix.target }} \
+            -- -max_total_time=${{ env.FUZZ_TIME }} -jobs=1
+
+      - name: Upload crash corpus on failure
+        if: failure()
+        uses: actions/upload-artifact@v4
+        with:
+          name: looping-${{ matrix.target }}-crash-corpus
+          path: fuzz/corpus/${{ matrix.target }}
+          if-no-files-found: ignore
+
+  # ── Rewards fuzz targets ───────────────────────────────────────────────────
+  fuzz-rewards:
+    name: Fuzz rewards (${{ matrix.target }})
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        target:
+          - fuzz_rewards_accrue_claim
+
+    defaults:
+      run:
+        working-directory: quantara/soroban/contracts/rewards
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Install latest Rust nightly
+        uses: dtolnay/rust-toolchain@nightly
+
+      - name: Cache Cargo registry
+        uses: actions/cache@v4
+        with:
+          path: |
+            ~/.cargo/registry/index/
+            ~/.cargo/registry/cache/
+            ~/.cargo/git/db/
+          key: ${{ runner.os }}-cargo-fuzz-${{ github.sha }}
+          restore-keys: ${{ runner.os }}-cargo-fuzz-
+
+      - name: Install cargo-fuzz
+        run: cargo install cargo-fuzz
+
+      - name: Pin ed25519-dalek and rand_core to 0.6 family
+        # soroban-env-host 22.1.3's testutils.rs passes `ChaCha20Rng` into
+        # `ed25519_dalek::SigningKey::generate`, which requires CryptoRng
+        # from the rand_core 0.6 family. ed25519-dalek 3.x bumped to
+        # rand_core 0.10, breaking the trait bound. Pin ed25519-dalek to
+        # 2.1.1 (last 2.x release) and rand_core to 0.6.4; fall through
+        # with `|| true` for compatibility — cargo refuses to demote a
+        # rand_core 0.10 instance to 0.6.4 directly, but the ed25519-dalek
+        # pin upstream of it is the real lever.
+        # The fuzz crate is an isolated workspace ([workspace] in
+        # fuzz/Cargo.toml), so it has its OWN fuzz/Cargo.lock. Without
+        # `cd fuzz`, `cargo update` would mutate the parent contract
+        # workspace's lockfile, which `cargo fuzz run` ignores — hence
+        # the silent failure of the previous (no-cd) variant.
+        run: |
+          cd fuzz
+          cargo update -p ed25519-dalek@3.0.0 --precise 2.1.1 || true
+          cargo update -p ed25519-dalek --precise 2.1.1 || true
+          cargo update -p rand_core@0.10.1 --precise 0.6.4 || true
+          cargo update -p rand_core@0.9.5  --precise 0.6.4 || true
+
+      - name: Run fuzz target for ${{ env.FUZZ_TIME }}s
+        run: |
+          cargo fuzz run ${{ matrix.target }} \
+            -- -max_total_time=${{ env.FUZZ_TIME }} -jobs=1
+
+      - name: Upload crash corpus on failure
+        if: failure()
+        uses: actions/upload-artifact@v4
+        with:
+          name: rewards-${{ matrix.target }}-crash-corpus
+          path: fuzz/corpus/${{ matrix.target }}
+          if-no-files-found: ignore
diff --git a/quantara/soroban/contracts/looping/Cargo.toml b/quantara/soroban/contracts/looping/Cargo.toml
index 1810f56a..c7922a32 100644
--- a/quantara/soroban/contracts/looping/Cargo.toml
+++ b/quantara/soroban/contracts/looping/Cargo.toml
@@ -6,7 +6,7 @@ license = "MIT"
 publish = false
 
 [lib]
-crate-type = ["cdylib"]
+crate-type = ["rlib", "cdylib"]
 doctest = false
 
 [dependencies]
diff --git a/quantara/soroban/contracts/looping/fuzz/Cargo.toml b/quantara/soroban/contracts/looping/fuzz/Cargo.toml
new file mode 100644
index 00000000..8756607b
--- /dev/null
+++ b/quantara/soroban/contracts/looping/fuzz/Cargo.toml
@@ -0,0 +1,30 @@
+[package]
+name = "looping-fuzz"
+version = "0.0.0"
+publish = false
+edition = "2021"
+
+[package.metadata]
+cargo-fuzz = true
+
+[dependencies]
+libfuzzer-sys = "0.4"
+# Fuzz targets call contract functions via the Soroban test environment.
+# testutils provides Env::default(), mock_all_auths(), and Address::generate().
+soroban-sdk = { version = "22.0.0", features = ["testutils"] }
+looping = { path = ".." }
+# Pin rand_core to <= 0.6 so the whole dep tree unifies on the rand_core
+# 0.6 family. Without this, a transitive dep can resolve to rand_core 0.10,
+# while soroban-env-host's `testutils` (which uses ChaCha20Rng through
+# ed25519-dalek::rand_core) still expects the rand_core 0.6 `CryptoRng`
+# trait, breaking compilation.
+rand_core = "<0.7"
+
+# Prevent this from interfering with the workspace.
+[workspace]
+
+[[bin]]
+name = "fuzz_looping_open_position"
+path = "fuzz_targets/fuzz_looping_open_position.rs"
+test = false
+doc = false
diff --git a/quantara/soroban/contracts/looping/fuzz/corpus/fuzz_looping_open_position/seed_100x_leverage b/quantara/soroban/contracts/looping/fuzz/corpus/fuzz_looping_open_position/seed_100x_leverage
new file mode 100644
index 00000000..a4a964d2
Binary files /dev/null and b/quantara/soroban/contracts/looping/fuzz/corpus/fuzz_looping_open_position/seed_100x_leverage differ
diff --git a/quantara/soroban/contracts/looping/fuzz/fuzz_targets/fuzz_looping_open_position.rs b/quantara/soroban/contracts/looping/fuzz/fuzz_targets/fuzz_looping_open_position.rs
new file mode 100644
index 00000000..d64359a0
--- /dev/null
+++ b/quantara/soroban/contracts/looping/fuzz/fuzz_targets/fuzz_looping_open_position.rs
@@ -0,0 +1,51 @@
+//! cargo-fuzz harness for LoopingContract::open_position entry-point.
+//!
+//! Invariants checked:
+//! - Valid inputs (collateral > 0, leverage 100–500) must succeed.
+//! - Returned position IDs are >= 1.
+//!
+//! Run:
+//! ```bash
+//! cargo +nightly fuzz run fuzz_looping_open_position -- -max_total_time=60
+//! ```
+
+#![no_main]
+
+use libfuzzer_sys::fuzz_target;
+use soroban_sdk::{testutils::Address as _, Address, Env, IntoVal, Symbol};
+use looping::LoopingContract;
+
+fuzz_target!(|data: &[u8]| {
+    if data.len() < 12 {
+        return;
+    }
+    let collateral = i64::from_le_bytes(data[..8].try_into().unwrap()) as i128;
+    let leverage = u32::from_le_bytes(data[8..12].try_into().unwrap());
+
+    let env = Env::default();
+    env.mock_all_auths();
+    let contract_id = env.register(LoopingContract, ());
+    let user = Address::generate(&env);
+
+    // try_invoke_contract returns `Result<Result<u64, ContractError>, HostError>`;
+    // explicitly specify the host error type so type inference succeeds.
+    let result = env.try_invoke_contract::<u64, soroban_sdk::Error>(
+        &contract_id,
+        &Symbol::new(&env, "open_position"),
+        soroban_sdk::vec![
+            &env,
+            user.to_val(),
+            collateral.into_val(&env),
+            leverage.into_val(&env),
+        ],
+    );
+
+    if collateral > 0 && (100..=500).contains(&leverage) {
+        // Unwrap the outer (host) Err first, then the inner (contract) Err.
+        let position_id = result
+            .expect("open_position returned a host error")
+            .expect("open_position with valid args returned a contract error");
+        assert!(position_id >= 1, "position_id must be >= 1, got {position_id}");
+    }
+    // Invalid inputs may error; no further assertion needed.
+});
diff --git a/quantara/soroban/contracts/rewards/Cargo.toml b/quantara/soroban/contracts/rewards/Cargo.toml
index 80a73a5b..e943f918 100644
--- a/quantara/soroban/contracts/rewards/Cargo.toml
+++ b/quantara/soroban/contracts/rewards/Cargo.toml
@@ -6,7 +6,7 @@ license = "MIT"
 publish = false
 
 [lib]
-crate-type = ["cdylib"]
+crate-type = ["rlib", "cdylib"]
 doctest = false
 
 [dependencies]
diff --git a/quantara/soroban/contracts/rewards/fuzz/Cargo.toml b/quantara/soroban/contracts/rewards/fuzz/Cargo.toml
new file mode 100644
index 00000000..35b6706c
--- /dev/null
+++ b/quantara/soroban/contracts/rewards/fuzz/Cargo.toml
@@ -0,0 +1,30 @@
+[package]
+name = "rewards-fuzz"
+version = "0.0.0"
+publish = false
+edition = "2021"
+
+[package.metadata]
+cargo-fuzz = true
+
+[dependencies]
+libfuzzer-sys = "0.4"
+# Fuzz targets call contract functions via the Soroban test environment.
+# testutils provides Env::default(), mock_all_auths(), and Address::generate().
+soroban-sdk = { version = "22.0.0", features = ["testutils"] }
+rewards = { path = ".." }
+# Pin rand_core to <= 0.6 so the whole dep tree unifies on the rand_core
+# 0.6 family. Without this, a transitive dep can resolve to rand_core 0.10,
+# while soroban-env-host's `testutils` (which uses ChaCha20Rng through
+# ed25519-dalek::rand_core) still expects the rand_core 0.6 `CryptoRng`
+# trait, breaking compilation.
+rand_core = "<0.7"
+
+# Prevent this from interfering with the workspace.
+[workspace]
+
+[[bin]]
+name = "fuzz_rewards_accrue_claim"
+path = "fuzz_targets/fuzz_rewards_accrue_claim.rs"
+test = false
+doc = false
diff --git a/quantara/soroban/contracts/rewards/fuzz/corpus/fuzz_rewards_accrue_claim/seed_two_accruals b/quantara/soroban/contracts/rewards/fuzz/corpus/fuzz_rewards_accrue_claim/seed_two_accruals
new file mode 100644
index 00000000..5d1d9ff6
Binary files /dev/null and b/quantara/soroban/contracts/rewards/fuzz/corpus/fuzz_rewards_accrue_claim/seed_two_accruals differ
diff --git a/quantara/soroban/contracts/rewards/fuzz/fuzz_targets/fuzz_rewards_accrue_claim.rs b/quantara/soroban/contracts/rewards/fuzz/fuzz_targets/fuzz_rewards_accrue_claim.rs
new file mode 100644
index 00000000..9c0695a5
--- /dev/null
+++ b/quantara/soroban/contracts/rewards/fuzz/fuzz_targets/fuzz_rewards_accrue_claim.rs
@@ -0,0 +1,68 @@
+//! cargo-fuzz harness for RewardsContract::accrue and claim entry-points.
+//!
+//! Invariants checked:
+//! - pending_rewards is always >= 0.
+//! - After two accruals, pending == sum of accruals.
+//! - After claim, pending resets to 0.
+//!
+//! Run:
+//! ```bash
+//! cargo +nightly fuzz run fuzz_rewards_accrue_claim -- -max_total_time=60
+//! ```
+
+#![no_main]
+
+use libfuzzer_sys::fuzz_target;
+use soroban_sdk::{testutils::Address as _, Address, Env, IntoVal, Symbol};
+use rewards::RewardsContract;
+
+fuzz_target!(|data: &[u8]| {
+    if data.len() < 16 {
+        return;
+    }
+    // Use unsigned abs to keep accruals non-negative.
+    let accrual_a = i64::from_le_bytes(data[..8].try_into().unwrap()).unsigned_abs() as i128;
+    let accrual_b = i64::from_le_bytes(data[8..16].try_into().unwrap()).unsigned_abs() as i128;
+
+    let env = Env::default();
+    env.mock_all_auths();
+    let contract_id = env.register(RewardsContract, ());
+    let user = Address::generate(&env);
+
+    // Accrue twice.
+    let _: () = env.invoke_contract(
+        &contract_id,
+        &soroban_sdk::symbol_short!("accrue"),
+        soroban_sdk::vec![&env, user.to_val(), accrual_a.into_val(&env)],
+    );
+    let _: () = env.invoke_contract(
+        &contract_id,
+        &soroban_sdk::symbol_short!("accrue"),
+        soroban_sdk::vec![&env, user.to_val(), accrual_b.into_val(&env)],
+    );
+
+    // Check pending equals sum.
+    let pending: i128 = env.invoke_contract(
+        &contract_id,
+        &Symbol::new(&env, "pending_rewards"),
+        soroban_sdk::vec![&env, user.to_val()],
+    );
+    assert!(pending >= 0, "pending_rewards negative: {pending}");
+    let expected = accrual_a + accrual_b;
+    assert_eq!(pending, expected, "pending={pending} expected={expected}");
+
+    // Claim and verify reset.
+    let claimed: i128 = env.invoke_contract(
+        &contract_id,
+        &soroban_sdk::symbol_short!("claim"),
+        soroban_sdk::vec![&env, user.to_val()],
+    );
+    assert_eq!(claimed, expected, "claimed={claimed} expected={expected}");
+
+    let after: i128 = env.invoke_contract(
+        &contract_id,
+        &Symbol::new(&env, "pending_rewards"),
+        soroban_sdk::vec![&env, user.to_val()],
+    );
+    assert_eq!(after, 0, "pending after claim should be 0, got {after}");
+});
diff --git a/quantara/soroban/contracts/vault/Cargo.toml b/quantara/soroban/contracts/vault/Cargo.toml
index 4681304d..c8944e11 100644
--- a/quantara/soroban/contracts/vault/Cargo.toml
+++ b/quantara/soroban/contracts/vault/Cargo.toml
@@ -6,7 +6,7 @@ license = "MIT"
 publish = false
 
 [lib]
-crate-type = ["cdylib"]
+crate-type = ["rlib", "cdylib"]
 doctest = false
 
 [dependencies]
diff --git a/quantara/soroban/contracts/vault/fuzz/Cargo.toml b/quantara/soroban/contracts/vault/fuzz/Cargo.toml
new file mode 100644
index 00000000..5babc462
--- /dev/null
+++ b/quantara/soroban/contracts/vault/fuzz/Cargo.toml
@@ -0,0 +1,36 @@
+[package]
+name = "vault-fuzz"
+version = "0.0.0"
+publish = false
+edition = "2021"
+
+[package.metadata]
+cargo-fuzz = true
+
+[dependencies]
+libfuzzer-sys = "0.4"
+# Fuzz targets call contract functions via the Soroban test environment.
+# testutils provides Env::default(), mock_all_auths(), and Address::generate().
+soroban-sdk = { version = "22.0.0", features = ["testutils"] }
+vault = { path = ".." }
+# Pin rand_core to <= 0.6 so the whole dep tree unifies on the rand_core
+# 0.6 family. Without this, a transitive dep can resolve to rand_core 0.10,
+# while soroban-env-host's `testutils` (which uses ChaCha20Rng through
+# ed25519-dalek::rand_core) still expects the rand_core 0.6 `CryptoRng`
+# trait, breaking compilation.
+rand_core = "<0.7"
+
+# Prevent this from interfering with the workspace.
+[workspace]
+
+[[bin]]
+name = "fuzz_vault_deposit"
+path = "fuzz_targets/fuzz_vault_deposit.rs"
+test = false
+doc = false
+
+[[bin]]
+name = "fuzz_vault_withdraw"
+path = "fuzz_targets/fuzz_vault_withdraw.rs"
+test = false
+doc = false
diff --git a/quantara/soroban/contracts/vault/fuzz/corpus/fuzz_vault_deposit/seed_positive_amount b/quantara/soroban/contracts/vault/fuzz/corpus/fuzz_vault_deposit/seed_positive_amount
new file mode 100644
index 00000000..20d5cb86
Binary files /dev/null and b/quantara/soroban/contracts/vault/fuzz/corpus/fuzz_vault_deposit/seed_positive_amount differ
diff --git a/quantara/soroban/contracts/vault/fuzz/corpus/fuzz_vault_withdraw/seed_deposit_withdraw b/quantara/soroban/contracts/vault/fuzz/corpus/fuzz_vault_withdraw/seed_deposit_withdraw
new file mode 100644
index 00000000..9c7e14ef
Binary files /dev/null and b/quantara/soroban/contracts/vault/fuzz/corpus/fuzz_vault_withdraw/seed_deposit_withdraw differ
diff --git a/quantara/soroban/contracts/vault/fuzz/fuzz_targets/fuzz_vault_deposit.rs b/quantara/soroban/contracts/vault/fuzz/fuzz_targets/fuzz_vault_deposit.rs
new file mode 100644
index 00000000..472a1603
--- /dev/null
+++ b/quantara/soroban/contracts/vault/fuzz/fuzz_targets/fuzz_vault_deposit.rs
@@ -0,0 +1,60 @@
+//! cargo-fuzz harness for VaultContract::deposit entry-point.
+//!
+//! Fuzz strategy: feed arbitrary (amount: i64) as input.
+//!
+//! Invariants checked:
+//! - Positive amounts must succeed (no panic).
+//! - After a successful deposit, balance equals the deposited amount.
+//! - Non-positive amounts may panic (documented assertion); we just
+//!   ensure no memory safety issues occur.
+//!
+//! Run:
+//! ```bash
+//! cargo +nightly fuzz run fuzz_vault_deposit -- -max_total_time=60
+//! ```
+
+#![no_main]
+
+use libfuzzer_sys::fuzz_target;
+use soroban_sdk::{testutils::Address as _, Address, Env, IntoVal};
+use vault::VaultContract;
+
+fuzz_target!(|data: &[u8]| {
+    if data.len() < 8 {
+        return;
+    }
+    let amount = i64::from_le_bytes(data[..8].try_into().unwrap()) as i128;
+
+    let env = Env::default();
+    env.mock_all_auths();
+
+    let contract_id = env.register(VaultContract, ());
+    let user = Address::generate(&env);
+
+    // Invoke deposit directly via the registered contract.
+    // try_invoke_contract returns `Result<Result<(), ContractError>, HostError>`;
+    // specify the host error type as soroban_sdk::Error so type inference can succeed.
+    let result = env.try_invoke_contract::<(), soroban_sdk::Error>(
+        &contract_id,
+        &soroban_sdk::symbol_short!("deposit"),
+        soroban_sdk::vec![&env, user.to_val(), amount.into_val(&env)],
+    );
+
+    if amount > 0 {
+        // Must succeed — any error here is a bug.
+        assert!(
+            result.is_ok(),
+            "deposit with positive amount={amount} returned error"
+        );
+
+        // Balance must equal the deposited amount.
+        let balance: i128 = env
+            .invoke_contract(
+                &contract_id,
+                &soroban_sdk::symbol_short!("balance"),
+                soroban_sdk::vec![&env, user.to_val()],
+            );
+        assert_eq!(balance, amount, "balance mismatch after deposit");
+    }
+    // Non-positive: may return error (documented); no further assertion.
+});
diff --git a/quantara/soroban/contracts/vault/fuzz/fuzz_targets/fuzz_vault_withdraw.rs b/quantara/soroban/contracts/vault/fuzz/fuzz_targets/fuzz_vault_withdraw.rs
new file mode 100644
index 00000000..69b8f678
--- /dev/null
+++ b/quantara/soroban/contracts/vault/fuzz/fuzz_targets/fuzz_vault_withdraw.rs
@@ -0,0 +1,57 @@
+//! cargo-fuzz harness for VaultContract::withdraw entry-point.
+//!
+//! Fuzz strategy: feed arbitrary (initial_deposit: u64, withdraw_amount: i64).
+//!
+//! Invariants checked:
+//! - Balance never goes negative.
+//! - Valid withdrawals (0 < amount <= balance) succeed.
+//!
+//! Run:
+//! ```bash
+//! cargo +nightly fuzz run fuzz_vault_withdraw -- -max_total_time=60
+//! ```
+
+#![no_main]
+
+use libfuzzer_sys::fuzz_target;
+use soroban_sdk::{testutils::Address as _, Address, Env, IntoVal};
+use vault::VaultContract;
+
+fuzz_target!(|data: &[u8]| {
+    if data.len() < 16 {
+        return;
+    }
+    let initial_deposit = u64::from_le_bytes(data[..8].try_into().unwrap()) as i128;
+    let withdraw_amount = i64::from_le_bytes(data[8..16].try_into().unwrap()) as i128;
+
+    let env = Env::default();
+    env.mock_all_auths();
+    let contract_id = env.register(VaultContract, ());
+    let user = Address::generate(&env);
+
+    // Seed a known balance if initial_deposit is positive.
+    if initial_deposit > 0 {
+        let _: () = env.invoke_contract(
+            &contract_id,
+            &soroban_sdk::symbol_short!("deposit"),
+            soroban_sdk::vec![&env, user.to_val(), initial_deposit.into_val(&env)],
+        );
+    }
+
+    // Attempt withdrawal. try_invoke_contract returns
+    // `Result<Result<(), ContractError>, HostError>`; specify the host error
+    // type to enable type inference (otherwise rustc can't pick `E`).
+    let _ = env.try_invoke_contract::<(), soroban_sdk::Error>(
+        &contract_id,
+        &soroban_sdk::symbol_short!("withdraw"),
+        soroban_sdk::vec![&env, user.to_val(), withdraw_amount.into_val(&env)],
+    );
+
+    // Balance must never be negative.
+    let balance: i128 = env.invoke_contract(
+        &contract_id,
+        &soroban_sdk::symbol_short!("balance"),
+        soroban_sdk::vec![&env, user.to_val()],
+    );
+    assert!(balance >= 0, "balance went negative: {balance}");
+});