diff --git a/editor/CMakeLists.txt b/editor/CMakeLists.txt
index a6ae855..8cc5f2f 100644
--- a/editor/CMakeLists.txt
+++ b/editor/CMakeLists.txt
@@ -4810,4 +4810,13 @@ target_link_libraries(step658_test PRIVATE
     tree_sitter_javascript tree_sitter_typescript
     tree_sitter_java tree_sitter_rust tree_sitter_go)
 
+add_executable(step659_test tests/step659_test.cpp)
+target_include_directories(step659_test PRIVATE src)
+target_link_libraries(step659_test PRIVATE
+    nlohmann_json::nlohmann_json
+    unofficial::tree-sitter::tree-sitter
+    tree_sitter_python tree_sitter_cpp tree_sitter_elisp
+    tree_sitter_javascript tree_sitter_typescript
+    tree_sitter_java tree_sitter_rust tree_sitter_go)
+
 # Step 12: Dear ImGui shell scaffolding created (main.cpp exists but not built due to dependencies)
diff --git a/editor/src/EntropyScannerModel.h b/editor/src/EntropyScannerModel.h
new file mode 100644
index 0000000..e9b9971
--- /dev/null
+++ b/editor/src/EntropyScannerModel.h
@@ -0,0 +1,65 @@
+#pragma once
+// Step 659: Entropy scanner - editor side
+
+#include <set>
+#include <string>
+#include <vector>
+
+struct EntropyObservation {
+    int duplicateSignatures = 0;
+    int similarModuleNames = 0;
+    int unusedExports = 0;
+};
+
+class EntropyScannerModel {
+public:
+    static EntropyObservation scan(const std::vector<std::string>& signatures,
+                                   const std::vector<std::string>& moduleNames,
+                                   const std::vector<std::string>& exports,
+                                   const std::set<std::string>& usedExports) {
+        EntropyObservation o;
+        o.duplicateSignatures = countDuplicates(signatures);
+        o.similarModuleNames = countPrefixSimilar(moduleNames);
+        o.unusedExports = countUnused(exports, usedExports);
+        return o;
+    }
+
+    static int entropyScore(const EntropyObservation& o) {
+        return o.duplicateSignatures + o.similarModuleNames + o.unusedExports;
+    }
+
+    static bool shouldSuggestRefactor(const EntropyObservation& o, int threshold = 3) {
+        return entropyScore(o) >= threshold;
+    }
+
+private:
+    static int countDuplicates(const std::vector<std::string>& values) {
+        std::set<std::string> seen;
+        int duplicates = 0;
+        for (const auto& v : values) {
+            if (!seen.insert(v).second) ++duplicates;
+        }
+        return duplicates;
+    }
+
+    static int countPrefixSimilar(const std::vector<std::string>& names) {
+        int similar = 0;
+        for (std::size_t i = 0; i < names.size(); ++i) {
+            for (std::size_t j = i + 1; j < names.size(); ++j) {
+                if (names[i].size() >= 3 && names[j].rfind(names[i].substr(0, 3), 0) == 0) {
+                    ++similar;
+                }
+            }
+        }
+        return similar;
+    }
+
+    static int countUnused(const std::vector<std::string>& exports,
+                           const std::set<std::string>& used) {
+        int unused = 0;
+        for (const auto& e : exports) {
+            if (used.find(e) == used.end()) ++unused;
+        }
+        return unused;
+    }
+};
diff --git a/editor/tests/step659_test.cpp b/editor/tests/step659_test.cpp
new file mode 100644
index 0000000..80fbb49
--- /dev/null
+++ b/editor/tests/step659_test.cpp
@@ -0,0 +1,24 @@
+// Step 659: Entropy scanner - editor side (12 tests)
+
+#include "EntropyScannerModel.h"
+#include <iostream>
+static int p=0,f=0;
+#define T(n) { std::cout<<"  "<<#n<<"... "; }
+#define P() { std::cout<<"PASS\n"; ++p; }
+#define F(m) { std::cout<<"FAIL: "<<m<<"\n"; ++f; }
+#define C(c,m) if(!(c)){F(m);return;}
+
+void t1(){T(scan_counts_duplicate_signatures);auto o=EntropyScannerModel::scan({"a()","a()"},{},{},{});C(o.duplicateSignatures==1,"dup");P();}
+void t2(){T(scan_counts_similar_module_names);auto o=EntropyScannerModel::scan({}, {"modAlpha","modBeta"},{},{});C(o.similarModuleNames>=1,"similar");P();}
+void t3(){T(scan_counts_unused_exports);auto o=EntropyScannerModel::scan({}, {},{"x","y"},{"x"});C(o.unusedExports==1,"unused");P();}
+void t4(){T(score_sums_components);EntropyObservation o{1,2,3};C(EntropyScannerModel::entropyScore(o)==6,"score");P();}
+void t5(){T(suggest_refactor_true_at_threshold);EntropyObservation o{1,1,1};C(EntropyScannerModel::shouldSuggestRefactor(o,3),"suggest");P();}
+void t6(){T(suggest_refactor_false_below_threshold);EntropyObservation o{1,0,0};C(!EntropyScannerModel::shouldSuggestRefactor(o,3),"no suggest");P();}
+void t7(){T(empty_inputs_yield_zeroes);auto o=EntropyScannerModel::scan({}, {}, {}, {});C(o.duplicateSignatures==0&&o.similarModuleNames==0&&o.unusedExports==0,"zero");P();}
+void t8(){T(multiple_duplicate_signatures_counted);auto o=EntropyScannerModel::scan({"a","a","a"},{},{},{});C(o.duplicateSignatures==2,"dups");P();}
+void t9(){T(used_export_not_counted_unused);auto o=EntropyScannerModel::scan({}, {}, {"x"}, {"x"});C(o.unusedExports==0,"used");P();}
+void t10(){T(threshold_parameter_changes_behavior);EntropyObservation o{1,1,0};C(EntropyScannerModel::shouldSuggestRefactor(o,2)&&!EntropyScannerModel::shouldSuggestRefactor(o,3),"threshold");P();}
+void t11(){T(similar_prefix_requires_min_length);auto o=EntropyScannerModel::scan({}, {"ab","ac"},{},{});C(o.similarModuleNames==0,"prefix");P();}
+void t12(){T(scan_combined_case);auto o=EntropyScannerModel::scan({"a","a"},{"modA","modB"},{"x"},{});C(EntropyScannerModel::entropyScore(o)>=3,"combined");P();}
+
+int main(){std::cout<<"Step 659: Entropy scanner\n";t1();t2();t3();t4();t5();t6();t7();t8();t9();t10();t11();t12();std::cout<<"\nResults: "<<p<<"/"<<(p+f)<<" passed\n";return f?1:0;}
diff --git a/progress.md b/progress.md
index 58f684a..cc3b5fc 100644
--- a/progress.md
+++ b/progress.md
@@ -13576,3 +13576,27 @@ apiary browser visibility into one Phase 40a readiness flow.
 - `editor/src/Phase40aIntegration.h` (`38` <= `600`)
 - `editor/tests/step658_test.cpp` within test-file size guidance (`20` lines)
 - Header-only architecture and naming conventions remain aligned with `ARCHITECTURE.md`
+
+### Step 659: Entropy scanner - editor-side
+**Status:** PASS (12/12 tests)
+
+Adds entropy scanning model for duplicate signatures, similar module names, and
+unused exports with scoring and refactor-threshold recommendation logic.
+
+**Files added:**
+- `editor/src/EntropyScannerModel.h` - entropy scan/scoring model
+- `editor/tests/step659_test.cpp` - 12 tests for scan signals and thresholds
+
+**Files modified:**
+- `editor/CMakeLists.txt` - `step659_test` target
+
+**Verification run:**
+- `cmake -S editor -B editor/build-native` - PASS
+- `cmake --build editor/build-native --target step659_test step658_test` - PASS
+- `./editor/build-native/step659_test` - PASS (12/12)
+- `./editor/build-native/step658_test` - PASS (8/8) regression coverage
+
+**Architecture gate check:**
+- `editor/src/EntropyScannerModel.h` (`65` <= `600`)
+- `editor/tests/step659_test.cpp` within test-file size guidance (`24` lines)
+- Header-only architecture and naming conventions remain aligned with `ARCHITECTURE.md`