diff --git a/barretenberg/cpp/src/barretenberg/bbapi/bbapi.test.cpp b/barretenberg/cpp/src/barretenberg/bbapi/bbapi.test.cpp
index 6867c97e9db1..75c822f111e7 100644
--- a/barretenberg/cpp/src/barretenberg/bbapi/bbapi.test.cpp
+++ b/barretenberg/cpp/src/barretenberg/bbapi/bbapi.test.cpp
@@ -1,6 +1,7 @@
 #include "barretenberg/bbapi/bbapi.hpp"
 #include "barretenberg/api/file_io.hpp"
 #include "barretenberg/bbapi/bbapi_shared.hpp"
+#include "barretenberg/chonk/private_execution_steps.hpp"
 #include "barretenberg/common/serialize.hpp"
 #include "barretenberg/common/utils.hpp"
 #include "barretenberg/serialize/test_helper.hpp"
@@ -113,3 +114,73 @@ TEST(BBApiInputValidation, VkWithCorrectSizeAccepted)
     std::vector<uint8_t> good_vk(expected_size, 0);
     EXPECT_NO_THROW(bbapi::validate_vk_size<VK>(good_vk));
 }
+
+// Helper: pack a vector of PrivateExecutionStepRaw into a byte buffer via msgpack.
+namespace {
+std::vector<uint8_t> pack_steps(const std::vector<PrivateExecutionStepRaw>& steps)
+{
+    std::stringstream ss;
+    msgpack::pack(ss, steps);
+    const std::string s = ss.str();
+    return { s.begin(), s.end() };
+}
+} // namespace
+
+TEST(BBApiInputValidation, MsgpackParseUncompressedAcceptsCleanInput)
+{
+    PrivateExecutionStepRaw step{
+        .bytecode = { 0xCA, 0xFE }, .witness = { 0xBE, 0xEF }, .vk = {}, .function_name = "test_fn"
+    };
+
+    auto buf = pack_steps({ step });
+    auto result = PrivateExecutionStepRaw::parse_uncompressed(buf);
+
+    ASSERT_EQ(result.size(), 1);
+    EXPECT_EQ(result[0].bytecode, step.bytecode);
+    EXPECT_EQ(result[0].witness, step.witness);
+    EXPECT_EQ(result[0].function_name, "test_fn");
+}
+
+TEST(BBApiInputValidation, MsgpackParseUncompressedRejectsTrailingData)
+{
+    PrivateExecutionStepRaw step{ .bytecode = {}, .witness = {}, .vk = {}, .function_name = "x" };
+
+    auto buf = pack_steps({ step });
+    buf.push_back(0x00);
+
+    EXPECT_THROW(PrivateExecutionStepRaw::parse_uncompressed(buf), std::invalid_argument);
+}
+
+TEST(BBApiInputValidation, MsgpackLoadAcceptsCleanFile)
+{
+    PrivateExecutionStepRaw step{ .bytecode = { 1, 2, 3 }, .witness = { 4, 5 }, .vk = {}, .function_name = "file_fn" };
+
+    auto buf = pack_steps({ step });
+
+    auto tmp = std::filesystem::temp_directory_path() / "bb_test_clean.msgpack";
+    std::ofstream out(tmp, std::ios::binary);
+    out.write(reinterpret_cast<const char*>(buf.data()), static_cast<std::streamsize>(buf.size()));
+    out.close();
+
+    auto result = PrivateExecutionStepRaw::load(tmp);
+    std::filesystem::remove(tmp);
+
+    ASSERT_EQ(result.size(), 1);
+    EXPECT_EQ(result[0].function_name, "file_fn");
+}
+
+TEST(BBApiInputValidation, MsgpackLoadRejectsTrailingData)
+{
+    PrivateExecutionStepRaw step{ .bytecode = {}, .witness = {}, .vk = {}, .function_name = "x" };
+
+    auto buf = pack_steps({ step });
+    buf.push_back(0x00);
+
+    auto tmp = std::filesystem::temp_directory_path() / "bb_test_tailed.msgpack";
+    std::ofstream out(tmp, std::ios::binary);
+    out.write(reinterpret_cast<const char*>(buf.data()), static_cast<std::streamsize>(buf.size()));
+    out.close();
+
+    EXPECT_THROW(PrivateExecutionStepRaw::load(tmp), std::invalid_argument);
+    std::filesystem::remove(tmp);
+}
diff --git a/barretenberg/cpp/src/barretenberg/chonk/private_execution_steps.cpp b/barretenberg/cpp/src/barretenberg/chonk/private_execution_steps.cpp
index beb335c22c72..d84d01155252 100644
--- a/barretenberg/cpp/src/barretenberg/chonk/private_execution_steps.cpp
+++ b/barretenberg/cpp/src/barretenberg/chonk/private_execution_steps.cpp
@@ -86,7 +86,12 @@ template <typename T> T unpack_from_file(const std::filesystem::path& filename)
     T result;
     std::string encoded_data(fsize, '\0');
     fin.read(encoded_data.data(), static_cast<std::streamsize>(fsize));
-    msgpack::unpack(encoded_data.data(), fsize).get().convert(result);
+    std::size_t offset = 0;
+    msgpack::unpack(encoded_data.data(), fsize, offset).get().convert(result);
+    if (offset != fsize) {
+        THROW std::invalid_argument("msgpack input has trailing data (" + std::to_string(fsize - offset) +
+                                    " extra bytes)");
+    }
     return result;
 }
 
@@ -121,7 +126,12 @@ std::vector<PrivateExecutionStepRaw> PrivateExecutionStepRaw::parse_uncompressed
 {
     std::vector<PrivateExecutionStepRaw> raw_steps;
     // Read with msgpack
-    msgpack::unpack(reinterpret_cast<const char*>(buf.data()), buf.size()).get().convert(raw_steps);
+    std::size_t offset = 0;
+    msgpack::unpack(reinterpret_cast<const char*>(buf.data()), buf.size(), offset).get().convert(raw_steps);
+    if (offset != buf.size()) {
+        THROW std::invalid_argument("msgpack input has trailing data (" + std::to_string(buf.size() - offset) +
+                                    " extra bytes)");
+    }
     // Unlike load_and_decompress, we don't need to decompress the bytecode and witness fields
     return raw_steps;
 }
diff --git a/barretenberg/cpp/src/barretenberg/polynomials/polynomial.hpp b/barretenberg/cpp/src/barretenberg/polynomials/polynomial.hpp
index 235dba268daa..bc97af4d891d 100644
--- a/barretenberg/cpp/src/barretenberg/polynomials/polynomial.hpp
+++ b/barretenberg/cpp/src/barretenberg/polynomials/polynomial.hpp
@@ -106,6 +106,7 @@ template <typename Fr> class Polynomial {
      */
     static Polynomial shiftable(size_t virtual_size)
     {
+        BB_ASSERT_GTE(virtual_size, NUM_ZERO_ROWS, "shiftable virtual_size must be >= NUM_ZERO_ROWS");
         return Polynomial(
             /*actual size*/ virtual_size - NUM_ZERO_ROWS, virtual_size, /*shiftable offset*/ NUM_ZERO_ROWS);
     }
@@ -114,6 +115,7 @@ template <typename Fr> class Polynomial {
      */
     static Polynomial shiftable(size_t size, size_t virtual_size)
     {
+        BB_ASSERT_GTE(size, NUM_ZERO_ROWS, "shiftable size must be >= NUM_ZERO_ROWS");
         return Polynomial(/*actual size*/ size - NUM_ZERO_ROWS, virtual_size, /*shiftable offset*/ NUM_ZERO_ROWS);
     }
     // Allow polynomials to be entirely reset/dormant
diff --git a/barretenberg/cpp/src/barretenberg/polynomials/polynomial_arithmetic.cpp b/barretenberg/cpp/src/barretenberg/polynomials/polynomial_arithmetic.cpp
index 3e2e5b7ddbd5..7fd42d2926a1 100644
--- a/barretenberg/cpp/src/barretenberg/polynomials/polynomial_arithmetic.cpp
+++ b/barretenberg/cpp/src/barretenberg/polynomials/polynomial_arithmetic.cpp
@@ -12,6 +12,7 @@
 #include <math.h>
 #include <memory.h>
 #include <memory>
+#include <mutex>
 
 namespace bb::polynomial_arithmetic {
 
@@ -19,6 +20,8 @@ namespace {
 
 template <typename Fr> std::shared_ptr<Fr[]> get_scratch_space(const size_t num_elements)
 {
+    static std::mutex scratch_mutex;
+    std::lock_guard lock(scratch_mutex);
     static std::shared_ptr<Fr[]> working_memory = nullptr;
     static size_t current_size = 0;
     if (num_elements > current_size) {
@@ -52,6 +55,8 @@ void scale_by_generator(Fr* coeffs,
                         const Fr& generator_shift,
                         const size_t generator_size)
 {
+    BB_ASSERT(generator_size % domain.num_threads == 0,
+              "generator_size must be divisible by num_threads to avoid silently skipping elements");
     parallel_for(domain.num_threads, [&](size_t j) {
         Fr thread_shift = generator_shift.pow(static_cast<uint64_t>(j * (generator_size / domain.num_threads)));
         Fr work_generator = generator_start * thread_shift;
diff --git a/barretenberg/cpp/src/barretenberg/polynomials/row_disabling_polynomial.hpp b/barretenberg/cpp/src/barretenberg/polynomials/row_disabling_polynomial.hpp
index ca1983f4535f..bd0c29241a4a 100644
--- a/barretenberg/cpp/src/barretenberg/polynomials/row_disabling_polynomial.hpp
+++ b/barretenberg/cpp/src/barretenberg/polynomials/row_disabling_polynomial.hpp
@@ -170,7 +170,7 @@ template <typename FF> struct RowDisablingPolynomial {
      * @param log_circuit_size
      * @return FF
      */
-    static FF evaluate_at_challenge(std::vector<FF> multivariate_challenge, const size_t log_circuit_size)
+    static FF evaluate_at_challenge(std::span<const FF> multivariate_challenge, const size_t log_circuit_size)
     {
         FF evaluation_at_multivariate_challenge{ 1 };
 
@@ -188,7 +188,7 @@ template <typename FF> struct RowDisablingPolynomial {
      * @param padding_indicator_array An array with first log_n entries equal to 1, and the remaining entries are 0.
      * @return FF
      */
-    static FF evaluate_at_challenge(std::span<FF> multivariate_challenge,
+    static FF evaluate_at_challenge(std::span<const FF> multivariate_challenge,
                                     const std::vector<FF>& padding_indicator_array)
     {
         FF evaluation_at_multivariate_challenge{ 1 };
diff --git a/barretenberg/cpp/src/barretenberg/stdlib/primitives/field/field.cpp b/barretenberg/cpp/src/barretenberg/stdlib/primitives/field/field.cpp
index ab689499cd84..b1d7ad6b01ca 100644
--- a/barretenberg/cpp/src/barretenberg/stdlib/primitives/field/field.cpp
+++ b/barretenberg/cpp/src/barretenberg/stdlib/primitives/field/field.cpp
@@ -1102,7 +1102,7 @@ void field_t<Builder>::evaluate_linear_identity(
     Builder* ctx = validate_context(a.context, b.context, c.context, d.context);
 
     if (a.is_constant() && b.is_constant() && c.is_constant() && d.is_constant()) {
-        BB_ASSERT_EQ(a.get_value() + b.get_value() + c.get_value() + d.get_value(), 0);
+        BB_ASSERT_EQ(a.get_value() + b.get_value() + c.get_value() + d.get_value(), 0, msg);
         return;
     }
 
@@ -1136,7 +1136,7 @@ void field_t<Builder>::evaluate_polynomial_identity(
     const field_t& a, const field_t& b, const field_t& c, const field_t& d, const std::string& msg)
 {
     if (a.is_constant() && b.is_constant() && c.is_constant() && d.is_constant()) {
-        BB_ASSERT((a.get_value() * b.get_value() + c.get_value() + d.get_value()).is_zero());
+        BB_ASSERT((a.get_value() * b.get_value() + c.get_value() + d.get_value()).is_zero(), msg);
         return;
     }
 
diff --git a/barretenberg/cpp/src/barretenberg/stdlib/primitives/field/field.hpp b/barretenberg/cpp/src/barretenberg/stdlib/primitives/field/field.hpp
index 249ff0488bdc..fa25cca7e73e 100644
--- a/barretenberg/cpp/src/barretenberg/stdlib/primitives/field/field.hpp
+++ b/barretenberg/cpp/src/barretenberg/stdlib/primitives/field/field.hpp
@@ -332,11 +332,12 @@ template <typename Builder_> class field_t {
         //      (this.v * this.mul + this.add) * inverse.v == 1;
         // created by applying `assert_is_not_zero` to `*this` coincides with the constraint created by
         // `divide_no_zero_check`, hence we can safely apply the latter instead of `/` operator.
-        auto* ctx = get_context();
         if (is_constant()) {
             BB_ASSERT(!get_value().is_zero(), "field_t::invert denominator is constant 0");
+            return field_t(fr::one()).divide_no_zero_check(*this);
         }
 
+        auto* ctx = get_context();
         if (get_value().is_zero() && !ctx->failed()) {
             ctx->failure("field_t::invert denominator is 0");
         }