diff --git a/barretenberg/cpp/src/barretenberg/acir_components_check/components_check.test.cpp b/barretenberg/cpp/src/barretenberg/acir_components_check/components_check.test.cpp
index 40e7d8fa16e2..cbcd198a46f1 100644
--- a/barretenberg/cpp/src/barretenberg/acir_components_check/components_check.test.cpp
+++ b/barretenberg/cpp/src/barretenberg/acir_components_check/components_check.test.cpp
@@ -544,13 +544,14 @@ TEST_F(AcirComponentsCheckTest, DetectsSplitComponents)
 
 TEST_F(AcirComponentsCheckTest, DetectsUnconstrainedWitnesses)
 {
+    constexpr uint32_t unconstrained_witness = 9;
     Acir::Circuit circuit = make_circuit({
         Acir::Opcode{ .value = Acir::Opcode::AssertZero{
                           .value = Acir::Expression{
                               .linear_combinations =
                                   {
                                       { bb::fr::one().to_buffer(), make_witness(8) },
-                                      { bb::fr(-1).to_buffer(), make_witness(9) },
+                                      { bb::fr(-1).to_buffer(), make_witness(unconstrained_witness) },
                                   },
                               .q_c = bb::fr::zero().to_buffer(),
                           } } },
@@ -559,8 +560,22 @@ TEST_F(AcirComponentsCheckTest, DetectsUnconstrainedWitnesses)
     auto constraints = circuit_serde_to_acir_format(circuit, IsMegaBuilder<AcirComponentsCheckBuilder>);
     AcirProgram program{ .constraints = constraints, .witness = {} };
     auto builder = create_circuit<AcirComponentsCheckBuilder>(program);
-    // Corrupt the circuit
-    builder.real_variable_index.resize(9);
+    // Corrupt the circuit without invalidating the builder's variable-index vectors. Shrinking
+    // real_variable_index makes debug STL builds abort inside the static analyzer before the
+    // components checker can classify the witness.
+    for (auto& block : builder.blocks.get()) {
+        auto replace_witness = [&](auto& wire) {
+            for (size_t row = 0; row < wire.size(); ++row) {
+                if (wire[row] == unconstrained_witness) {
+                    wire[row] = builder.zero_idx();
+                }
+            }
+        };
+        replace_witness(block.w_l());
+        replace_witness(block.w_r());
+        replace_witness(block.w_o());
+        replace_witness(block.w_4());
+    }
 
     acir_components_check::ComponentsChecker checker(circuit, builder);
     auto errors = checker.check();
diff --git a/ci3/source_cache b/ci3/source_cache
index f9d88c651601..b2be34c9c985 100644
--- a/ci3/source_cache
+++ b/ci3/source_cache
@@ -65,8 +65,11 @@ function cache_persistent {
 
   cat | gzip > "$tmpfile"
 
-  # Write to Redis (synchronous)
-  cat "$tmpfile" | redis_cli -x SETEX "$key" "$expire" &>/dev/null
+  # Write to Redis (synchronous) when available. The S3 upload below is the
+  # persistent fallback when the runner cannot reach Redis.
+  if [ "$CI_REDIS_AVAILABLE" -eq 1 ]; then
+    cat "$tmpfile" | redis_cli -x SETEX "$key" "$expire" &>/dev/null
+  fi
 
   # Write to S3 in background
   {
diff --git a/ci3/source_redis b/ci3/source_redis
index 6bf9a3b94809..765515336f85 100644
--- a/ci3/source_redis
+++ b/ci3/source_redis
@@ -81,7 +81,11 @@ function redis_cli {
 }
 
 function redis_setexz {
-  gzip | redis_cli -x SETEX $1 $2 &>/dev/null
+  if [ "$CI_REDIS_AVAILABLE" -eq 1 ]; then
+    gzip | redis_cli -x SETEX "$1" "$2" &>/dev/null
+  else
+    cat >/dev/null
+  fi
 }
 
 function redis_getz {