diff --git a/editor/src/ConstrainedTaskitemIntegration.h b/editor/src/ConstrainedTaskitemIntegration.h
index 640053c..465cb23 100644
--- a/editor/src/ConstrainedTaskitemIntegration.h
+++ b/editor/src/ConstrainedTaskitemIntegration.h
@@ -8,6 +8,7 @@
 #include <nlohmann/json.hpp>
 
 #include "ConstraintViolationDiagnostics.h"
+#include "ConstraintSchemaFailurePacket.h"
 
 using json = nlohmann::json;
 
@@ -38,7 +39,7 @@ public:
         auto validation = TypedTaskitemContractSchema::parseAndValidate(request.taskitemJson);
         if (!validation.valid) {
             result.schemaErrors = validation.errors;
-            result.diagnostics = schemaFailurePacket(validation.errors);
+            result.diagnostics = makeUnderConstrainedContractPacket(validation.errors);
             return result;
         }
 
@@ -66,21 +67,4 @@ public:
         result.executed = result.diagnostics.ok;
         return result;
     }
-
-private:
-    static ConstraintDiagnosticPacket schemaFailurePacket(
-        const std::vector<std::string>& errors) {
-        ConstraintDiagnosticPacket packet;
-        packet.ok = false;
-        packet.recommendedAction = "escalate";
-        for (const auto& error : errors) {
-            packet.violations.push_back({
-                "under_constrained_contract",
-                "Taskitem contract failed schema validation",
-                error,
-                false
-            });
-        }
-        return packet;
-    }
 };
diff --git a/editor/src/ConstraintSchemaFailurePacket.h b/editor/src/ConstraintSchemaFailurePacket.h
new file mode 100644
index 0000000..f263859
--- /dev/null
+++ b/editor/src/ConstraintSchemaFailurePacket.h
@@ -0,0 +1,23 @@
+#pragma once
+// Sprint 27 refactor: shared schema-failure packet helper
+
+#include <string>
+#include <vector>
+
+#include "ConstraintViolationDiagnostics.h"
+
+inline ConstraintDiagnosticPacket makeUnderConstrainedContractPacket(
+    const std::vector<std::string>& errors) {
+    ConstraintDiagnosticPacket packet;
+    packet.ok = false;
+    packet.recommendedAction = "escalate";
+    for (const auto& error : errors) {
+        packet.violations.push_back({
+            "under_constrained_contract",
+            "Taskitem contract failed schema validation",
+            error,
+            false
+        });
+    }
+    return packet;
+}
diff --git a/editor/src/PreApplyValidationGate.h b/editor/src/PreApplyValidationGate.h
index d1c3ee7..77c11d0 100644
--- a/editor/src/PreApplyValidationGate.h
+++ b/editor/src/PreApplyValidationGate.h
@@ -9,6 +9,7 @@
 #include <nlohmann/json.hpp>
 
 #include "ConstraintViolationDiagnostics.h"
+#include "ConstraintSchemaFailurePacket.h"
 
 using json = nlohmann::json;
 
@@ -37,7 +38,7 @@ public:
 
         auto schema = TypedTaskitemContractSchema::parseAndValidate(taskitemJson);
         if (!schema.valid) {
-            result.diagnostics = schemaFailurePacket(schema.errors);
+            result.diagnostics = makeUnderConstrainedContractPacket(schema.errors);
             return result;
         }
         result.contract = schema.contract;
@@ -111,20 +112,4 @@ private:
         }
         return violations.empty() ? "proceed" : "retry";
     }
-
-    static ConstraintDiagnosticPacket schemaFailurePacket(
-        const std::vector<std::string>& errors) {
-        ConstraintDiagnosticPacket packet;
-        packet.ok = false;
-        packet.recommendedAction = "escalate";
-        for (const auto& error : errors) {
-            packet.violations.push_back({
-                "under_constrained_contract",
-                "Taskitem contract failed schema validation",
-                error,
-                false
-            });
-        }
-        return packet;
-    }
 };
diff --git a/progress.md b/progress.md
index 832cf2c..90879df 100644
--- a/progress.md
+++ b/progress.md
@@ -8930,3 +8930,39 @@ notes.
 - **New tests in this sprint plan:** 112/112 passing
 - **Phase 27a (524-528):** 56/56 passing
 - **Phase 27b (529-533):** 56/56 passing
+
+## Sprint 27 End Refactor Pass (Architecture Compliance)
+
+Performed a dedicated post-sprint refactor pass to reduce duplication and
+re-validate architecture constraints without changing runtime behavior.
+
+**Refactors applied:**
+- `editor/src/ConstraintSchemaFailurePacket.h`
+  - extracted shared helper `makeUnderConstrainedContractPacket(...)`
+  - centralized schema-failure diagnostics payload construction
+- `editor/src/ConstrainedTaskitemIntegration.h`
+  - replaced inline schema-failure packet builder with shared helper usage
+  - removed duplicate private schema-failure implementation
+- `editor/src/PreApplyValidationGate.h`
+  - replaced inline schema-failure packet builder with shared helper usage
+  - removed duplicate private schema-failure implementation
+
+**Architecture compliance audit:**
+- Header size gate (`<=600` lines): PASS across Sprint 27 modules
+  - largest audited header: `editor/src/ConstraintViolationDiagnostics.h` (`169` lines)
+- `goto` usage in Sprint 27 runtime path: PASS (none)
+- Stale TODO markers in Sprint 27 modules: PASS (none)
+- Header-only pattern for Sprint 27 additions: PASS
+
+**Refactor verification run:**
+- `cmake --build editor/build-native --target step524_test step525_test step526_test step527_test step528_test step529_test step530_test step531_test step532_test step533_test` - PASS
+- `./editor/build-native/step524_test` - PASS (12/12)
+- `./editor/build-native/step525_test` - PASS (12/12)
+- `./editor/build-native/step526_test` - PASS (12/12)
+- `./editor/build-native/step527_test` - PASS (12/12)
+- `./editor/build-native/step528_test` - PASS (8/8)
+- `./editor/build-native/step529_test` - PASS (12/12)
+- `./editor/build-native/step530_test` - PASS (12/12)
+- `./editor/build-native/step531_test` - PASS (12/12)
+- `./editor/build-native/step532_test` - PASS (12/12)
+- `./editor/build-native/step533_test` - PASS (8/8)