diff --git a/.github/workflows/verify.yml b/.github/workflows/verify.yml
index 57063ad..b86bace 100644
--- a/.github/workflows/verify.yml
+++ b/.github/workflows/verify.yml
@@ -8,7 +8,11 @@ on:
 
 jobs:
   verify:
-    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest, windows-latest]
+    runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v4
 
@@ -24,12 +28,24 @@ jobs:
       - name: Build Plugin
         run: ./gradlew buildPlugin
 
+      # 인코딩 회귀 테스트(이슈 #2/#4 포함) 실행.
+      # Windows 매트릭스에서 비-UTF-8 OS 동작까지 검증한다.
+      - name: Run Tests
+        run: ./gradlew test
+
       - name: Verify Plugin (deprecated API + compatibility)
         run: ./gradlew verifyPlugin
 
+      - name: Upload Test Report
+        if: always()
+        uses: actions/upload-artifact@v4
+        with:
+          name: test-report-${{ matrix.os }}
+          path: build/reports/tests/
+
       - name: Upload Verification Report
         if: always()
         uses: actions/upload-artifact@v4
         with:
-          name: plugin-verification-report
+          name: plugin-verification-report-${{ matrix.os }}
           path: build/reports/pluginVerifier/
diff --git a/src/main/kotlin/com/codingtestkit/service/CodeRunner.kt b/src/main/kotlin/com/codingtestkit/service/CodeRunner.kt
index ad00448..5663e5b 100644
--- a/src/main/kotlin/com/codingtestkit/service/CodeRunner.kt
+++ b/src/main/kotlin/com/codingtestkit/service/CodeRunner.kt
@@ -494,8 +494,13 @@ else console.log(_result);
     }
 
     private fun detectPython(): String {
-        return findExecutable("python3", "/usr/bin/python3", "/usr/local/bin/python3",
-            "/opt/homebrew/bin/python3", "python")
+        // Windows는 python3가 아니라 python 명령이 일반적
+        return if (isWindows) {
+            findExecutable("python", "python3")
+        } else {
+            findExecutable("python3", "/usr/bin/python3", "/usr/local/bin/python3",
+                "/opt/homebrew/bin/python3", "python")
+        }
     }
 
     private fun detectKotlinc(): String {
@@ -560,19 +565,36 @@ else console.log(_result);
         return findExecutable("node", "/usr/local/bin/node", "/opt/homebrew/bin/node")
     }
 
+    private val isWindows: Boolean = System.getProperty("os.name").lowercase().contains("win")
+
     private fun findExecutable(vararg candidates: String): String {
         for (candidate in candidates) {
-            // 절대 경로면 파일 존재 확인
-            if (candidate.startsWith("/") && File(candidate).exists()) return candidate
+            // 절대 경로 후보 (Unix: /usr/..., Windows: C:\...)
+            if (candidate.startsWith("/") || candidate.matches(Regex("^[A-Za-z]:[\\\\/].*"))) {
+                if (File(candidate).exists()) return candidate
+                // Windows 실행파일은 .exe 확장자 보정
+                if (isWindows && !candidate.endsWith(".exe")) {
+                    val withExe = File("$candidate.exe")
+                    if (withExe.exists()) return withExe.absolutePath
+                }
+                continue
+            }
 
-            // PATH에서 찾기
+            // PATH에서 찾기: Windows는 where, 그 외는 which.
+            // (Git Bash의 which는 ProcessBuilder가 실행 못 하는 MSYS 경로 /c/... 를 반환하므로 where 사용)
             try {
-                val proc = ProcessBuilder("which", candidate).start()
-                val result = proc.inputStream.bufferedReader().readText().trim()
-                if (proc.waitFor() == 0 && result.isNotBlank()) return result
+                val locator = if (isWindows) "where" else "which"
+                val proc = ProcessBuilder(locator, candidate).start()
+                val output = proc.inputStream.bufferedReader().readText()
+                val ok = proc.waitFor() == 0
+                // where는 여러 줄을 반환할 수 있으므로 실제로 존재하는 첫 경로를 선택
+                val resolved = output.lineSequence()
+                    .map { it.trim() }
+                    .firstOrNull { it.isNotBlank() && File(it).exists() }
+                if (ok && resolved != null) return resolved
             } catch (_: Exception) {}
         }
-        return candidates.first() // fallback: 원래 이름 그대로
+        return candidates.first() // fallback: 원래 이름 그대로 (PATH 탐색에 맡김)
     }
 
     fun getDetectedPaths(): Map<String, String> = mapOf(
diff --git a/src/main/kotlin/com/codingtestkit/service/ProblemFileManager.kt b/src/main/kotlin/com/codingtestkit/service/ProblemFileManager.kt
index 3031edf..ddc36ee 100644
--- a/src/main/kotlin/com/codingtestkit/service/ProblemFileManager.kt
+++ b/src/main/kotlin/com/codingtestkit/service/ProblemFileManager.kt
@@ -196,7 +196,8 @@ object ProblemFileManager {
     }
 
     private fun sanitizeFolderName(name: String): String {
-        return name.replace(Regex("[^a-zA-Z0-9가-힣_\\-() ]"), "_")
+        // 파일/폴더명에 안전한 . 와 + 도 보존한다 (예: 백준 1000 "A+B").
+        return name.replace(Regex("[^a-zA-Z0-9가-힣_.+\\-() ]"), "_")
             .replace(Regex("_+"), "_")
             .trim()
             .take(60)
diff --git a/src/main/kotlin/com/codingtestkit/service/SolvedAcApi.kt b/src/main/kotlin/com/codingtestkit/service/SolvedAcApi.kt
index a9cc72b..7782e5e 100644
--- a/src/main/kotlin/com/codingtestkit/service/SolvedAcApi.kt
+++ b/src/main/kotlin/com/codingtestkit/service/SolvedAcApi.kt
@@ -261,11 +261,13 @@ object SolvedAcApi {
     private fun toSubscript(s: String): String = s.map { subscriptMap[it] ?: it }.joinToString("")
 
     fun levelToString(level: Int): String {
-        if (level == 0) return "Unrated"
+        // 유효 레벨은 1~30 (Bronze V ~ Ruby I). 그 밖(0, 음수, 31+)은 모두 Unrated.
+        // 범위 밖 입력에서 rankIdx가 음수가 되어 ArrayIndexOutOfBounds가 나던 문제 방지.
+        if (level < 1 || level > 30) return "Unrated"
         val tiers = arrayOf("Bronze", "Silver", "Gold", "Platinum", "Diamond", "Ruby")
         val ranks = arrayOf("V", "IV", "III", "II", "I")
         val tierIdx = (level - 1) / 5
         val rankIdx = (level - 1) % 5
-        return if (tierIdx in tiers.indices) "${tiers[tierIdx]} ${ranks[rankIdx]}" else "Unrated"
+        return "${tiers[tierIdx]} ${ranks[rankIdx]}"
     }
 }