diff --git a/.Jules/palette.md b/.Jules/palette.md
index c3dc3c5..98c341f 100644
--- a/.Jules/palette.md
+++ b/.Jules/palette.md
@@ -1,3 +1,6 @@
-## 2024-05-24 - [Add smooth transitions for a tags but respect user motion preferences]
-**Learning:** Adding CSS transitions (`transition: all`) can create unintended animations and performance issues. Also, animations can cause problems for users with vestibular motion disorders.
-**Action:** When adding CSS transitions, explicitly specify properties (e.g., `background-color`, `outline-color`) instead of `transition: all`. Always include a `@media (prefers-reduced-motion: reduce)` override to set `transition: none` for accessibility.
\ No newline at end of file
+## 2024-05-24 - [a 태그에 부드러운 트랜지션 추가 및 사용자의 모션 설정 존중]
+**Learning:** CSS 트랜지션(`transition: all`)을 추가하면 의도치 않은 애니메이션과 성능 문제를 일으킬 수 있습니다. 또한, 애니메이션은 전정 운동 장애가 있는 사용자에게 문제를 유발할 수 있습니다.
+**Action:** CSS 트랜지션을 추가할 때 `transition: all` 대신 속성(`background-color`, `outline-color` 등)을 명시적으로 지정하십시오. 접근성을 위해 항상 `@media (prefers-reduced-motion: reduce)` 오버라이드를 포함하여 `transition: none`으로 설정하십시오.
+## 2024-07-10 - 다크 모드 지원 및 지역화 일관성 확보
+**Learning:** `html4tree` CLI로 생성되는 정적 HTML에서 사용자는 네이티브 다크 모드를 기대하며(접근성, 가독성 문제), `<nav>` 레이블("Directory listing")이 다른 UI와 다르게 영문으로 되어 있어 스크린 리더 환경 등에서 지역화(Localization) 일관성을 해칩니다.
+**Action:** `prefers-color-scheme: dark` 미디어 쿼리를 CSS에 추가하여 네이티브 다크 모드를 지원하고, `<nav aria-label="Directory listing">`을 `<nav aria-label="디렉토리 목록">`으로 수정하여 UI를 한국어로 통일했습니다.
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
new file mode 100644
index 0000000..b46b5e1
--- /dev/null
+++ b/.github/workflows/ci.yml
@@ -0,0 +1,46 @@
+name: CI
+
+on:
+  push:
+    branches: [master]
+  pull_request:
+    branches: [master]
+
+permissions:
+  contents: read
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
+      # Gradle 5.1.1 (wrapper) supports up to Java 11. Uses the runner image's
+      # bundled Temurin JDK instead of actions/setup-java to keep every
+      # workflow dependency hash-pinned (Scorecard Pinned-Dependencies).
+      - name: Use preinstalled Temurin JDK 11
+        run: |
+          echo "JAVA_HOME=$JAVA_HOME_11_X64" >> "$GITHUB_ENV"
+          echo "$JAVA_HOME_11_X64/bin" >> "$GITHUB_PATH"
+      - name: Build and test (includes jacoco coverage verification)
+        run: ./gradlew build --no-daemon
+      - name: Report coverage gaps on failure
+        if: failure()
+        run: |
+          python3 - <<'PY'
+          import xml.etree.ElementTree as ET
+          try:
+              tree = ET.parse('build/reports/jacoco/test/jacocoTestReport.xml')
+          except OSError:
+              print('no jacoco XML report found')
+              raise SystemExit(0)
+          for pkg in tree.iter('package'):
+              for sf in pkg.iter('sourcefile'):
+                  missed = [l.get('nr') for l in sf.iter('line') if l.get('mi') != '0']
+                  if missed:
+                      print(f"{pkg.get('name')}/{sf.get('name')}: missed instructions on lines {', '.join(missed)}")
+              for cls in pkg.iter('class'):
+                  for m in cls.iter('method'):
+                      counter = next((c for c in m.iter('counter') if c.get('type') == 'INSTRUCTION'), None)
+                      if counter is not None and counter.get('covered') == '0':
+                          print(f"uncovered method: {cls.get('name')}.{m.get('name')}{m.get('desc')} (line {m.get('line')})")
+          PY
diff --git a/.jules/bolt.md b/.jules/bolt.md
index a9253e7..82fe47b 100644
--- a/.jules/bolt.md
+++ b/.jules/bolt.md
@@ -12,3 +12,4 @@
 ## 2024-07-08 - URL Encoding String Allocation Bottleneck
 **Learning:** `byte.toString(16).padStart(2, '0').toUpperCase()` inside a loop allocating up to 3 strings per reserved byte in a hot path causes significant GC pressure. This is a common but dangerous anti-pattern in Kotlin when processing large strings or numerous files in directory crawlers.
 **Action:** Replace chained string operations with direct character mapping and bitwise operations (`ushr`, `and`) when building formatted hex output, which avoids intermediate string creation entirely. Ensure 100% branch coverage with test inputs spanning both < 10 and > 9 hex values.
+## 2026-07-10 - Expensive OS stat calls before cheap in-memory checks\n**Learning:** In Kotlin/Java, checking file properties (like `isDirectory` or `isSymbolicLink`) via `java.nio.file.Files` requires allocating `Path` objects and performs expensive native OS stat calls. When processing file listings, always short-circuit filesystem checks by testing against exclusion lists (using cheap in-memory string operations) before calling methods that touch the filesystem.\n**Action:** Re-ordered conditionals to check `exclude` sets before invoking `Files.isDirectory` and `Files.isSymbolicLink`.
diff --git a/.jules/palette.md b/.jules/palette.md
index b8df5bd..c426231 100644
--- a/.jules/palette.md
+++ b/.jules/palette.md
@@ -13,3 +13,11 @@
 ## 2024-06-25 - Directory Listing Navigation Landmark
 **Learning:** Generated directory listings act as navigation regions, and screen readers benefit when the listing is announced separately from the page's main content.
 **Action:** Wrap generated directory listing `<ul>` elements in `<nav aria-label="Directory listing">` while keeping the surrounding semantic `<main>` structure.
+
+## 2024-07-09 - CLI HTML Typography and Dark Mode
+**Learning:** Even statically generated directory listings need proper typography and color scheme support. Without a constrained max-width, line length becomes unreadable on large monitors. Without dark mode support (`prefers-color-scheme: dark`), opening the generated HTML page can cause sudden visual strain for users on dark-themed OS settings. In addition, when combining multiple media queries, `@media (prefers-color-scheme: dark)` should be placed at the end of the stylesheet to prevent flash of unstyled content (FOUC) and properly override base styles.
+**Action:** Always include basic typography constraints (max-width, line-height, system font) and dark mode media queries (at the end of the CSS block) for any CLI tool that generates HTML output to ensure accessibility, visual comfort, and reliable styling prioritization.
+
+## 2026-07-10 - ARIA Label Language Matching
+**Learning:** Screen readers rely on the document's language attribute (`lang="ko"`) to select the appropriate pronunciation engine. If semantic descriptors like `aria-label` are provided in a language different from the document language (e.g., English text in a Korean document), they may be mispronounced or skipped entirely, breaking accessibility.
+**Action:** Always ensure that `aria-label`, `alt` text, and other hidden semantic text strings match the language specified in the document's `<html lang="...">` tag for proper localization and screen reader compatibility.
diff --git a/AGENTS.md b/AGENTS.md
new file mode 100644
index 0000000..db03c2d
--- /dev/null
+++ b/AGENTS.md
@@ -0,0 +1,38 @@
+# AGENTS.md
+
+Cross-agent conventions for this repo (Claude, Codex, Cursor, opencode, and any
+other coding agent). html4tree is a Kotlin CLI (Gradle build) that generates
+`index.html` directory listings.
+
+<!-- BEGIN cwl-agent-guidance -->
+## Agent guidance (CWL governance)
+
+### Security & review gate
+
+- Every PR runs a central, required **Security Scan** gate: `osv-scan` +
+  `dependency-review` (diff-scoped) and `trivy-fs` (repo-wide, CRITICAL/HIGH,
+  fixable). It runs on every PR base, **including stacked PRs**.
+- A failing **`trivy-fs` is a REAL finding, not a flake.** Read the job log — it
+  prints each finding's rule id / severity / file — or the run's SARIF results.
+  Then **remediate**:
+  - Dependency vulnerability: bump the offending library in `build.gradle`
+    (e.g. the Kotlin stdlib or `clikt` version, or a transitive dep).
+  - Genuine false positive only: add a narrow, documented
+    `.trivyignore` / `.trivyignore.yaml` entry.
+  - This repo has no Dockerfile or k8s manifests today; if you add either,
+    fix image/misconfig findings at the source.
+- Do **NOT** weaken or disable the gate. A local `trivy` scan with a stale DB
+  misses findings — run `trivy --download-db-only` first, and scan the **merge
+  ref**, not just the PR head.
+- The org `code_scanning` ruleset is intentionally **CodeQL-only** (multiple
+  code-scanning tools can't converge on one PR ref). Gating is by the Security
+  Scan **job result**, not the code_scanning rule — don't add tools to that rule.
+
+### Code exploration
+
+- This repo has **no `.codegraph/` index**, so use normal search (grep/find,
+  Read) to locate and understand code. If a `.codegraph/` directory is later
+  added at the repo root, prefer CodeGraph — `codegraph explore "<query>"` or the
+  code-review-graph MCP tools — BEFORE grep/find, since it surfaces
+  callers/callees/impact that text search misses.
+<!-- END cwl-agent-guidance -->
diff --git a/CHANGELOG.md b/CHANGELOG.md
new file mode 100644
index 0000000..2973535
--- /dev/null
+++ b/CHANGELOG.md
@@ -0,0 +1,5 @@
+# CHANGELOG
+
+## [Unreleased]
+### 추가
+- Palette: 생성된 HTML 파일의 가독성 향상 및 시각적 편안함을 위해 다크 모드(`prefers-color-scheme: dark`) 지원 및 `body` 요소의 기본 타이포그래피(시스템 폰트 적용, 중앙 정렬 및 최대 너비 제한) 스타일 추가.
diff --git a/src/main/kotlin/html4tree/main.kt b/src/main/kotlin/html4tree/main.kt
index c4877e2..afe94d1 100644
--- a/src/main/kotlin/html4tree/main.kt
+++ b/src/main/kotlin/html4tree/main.kt
@@ -123,16 +123,15 @@ fun process_ignore_file(curr_dir: File): Set<String> {
     // 보안 향상: 파일 크기(1MB 제한) 및 줄 수(1000줄), 정규식 길이(100자)를 제한하여 ReDoS 및 메모리 고갈(OOM) 방지
     if(ignore_file.isFile && !Files.isSymbolicLink(ignore_file.toPath()) && ignore_file.length() <= 1048576){
        val ignored_regexes = mutableListOf<Regex>()
-       var patternCount = 0
 
        ignore_file.useLines { lines ->
            for ((lineIndex, it) in lines.withIndex()) {
-               if (lineIndex >= 1000 || patternCount >= 1000) break
+               // 줄 수 제한이 패턴 수도 함께 상한(줄당 최대 1개 패턴)하므로 별도 패턴 카운터는 불필요
+               if (lineIndex >= 1000) break
                val pattern = it.trim()
                if (pattern.isNotEmpty() && pattern.length <= 100) {
                    try {
                        ignored_regexes.add(("^"+pattern+"$").toRegex())
-                       patternCount++
                    } catch (_: IllegalArgumentException) {
                    }
                }
@@ -176,6 +175,15 @@ fun process_dir(curr_dir: File){
 
     val css = """
               <style>
+              body {
+                font-family: system-ui, -apple-system, sans-serif;
+                max-width: 800px;
+                margin: 0 auto;
+                padding: 1rem;
+                color: #24292e;
+                background-color: #ffffff;
+                line-height: 1.5;
+              }
               ul {
                 list-style-type: none;
                 padding-left: 0;
@@ -198,6 +206,19 @@ fun process_dir(curr_dir: File){
                   transition: none;
                 }
               }
+              @media (prefers-color-scheme: dark) {
+                body {
+                  color: #c9d1d9;
+                  background-color: #0d1117;
+                }
+                a {
+                  color: #58a6ff;
+                }
+                a:hover, a:focus-visible {
+                  background-color: #161b22;
+                  outline-color: #58a6ff;
+                }
+              }
               </style>
               """
 
@@ -214,7 +235,7 @@ fun process_dir(curr_dir: File){
      <body>
        <main>
          <h1>${curr_dir.getName().escapeHtml()}</h1>
-         <nav aria-label="Directory listing">
+         <nav aria-label="디렉토리 목록">
          <ul>
             <li><a style="display:block; width:100%" href="./.." aria-label="상위 디렉토리로 이동"><span aria-hidden="true">&#x21B0;</span> ..</a></li>
 """ 
@@ -225,14 +246,17 @@ fun process_dir(curr_dir: File){
         val dir_files: MutableList<File> = curr_dir.listFiles()?.toMutableList() ?: mutableListOf()
         dir_files.sortWith(compareBy ({it.name}) )
         dir_files.forEach {
-           val isLinkedDirectory = Files.isDirectory(it.toPath(), LinkOption.NOFOLLOW_LINKS)
-           if((it.getName() !in exclude) && (isLinkedDirectory || !it.isDirectory()) && !Files.isSymbolicLink(it.toPath())) {
-              val fileName = it.getName()
-              val encodedHref = if (isLinkedDirectory) { "./${fileName.urlEncodePath()}/" } else { "./${fileName.urlEncodePath()}" }
-              val ariaLabel = "${fileName} ${if (isLinkedDirectory) { "디렉토리" } else { "파일" }}".escapeHtml()
-              val icon = if (isLinkedDirectory) { "&#128193;" } else { "&rtrif;" }
-              l.append("""          <li><a style="display:block; width:100%" href="${encodedHref}" aria-label="${ariaLabel}"><span aria-hidden="true">${icon}</span> ${fileName.escapeHtml()}</a></li>""")
-              l.append('\n')
+           val fileName = it.getName()
+           // ⚡ Bolt Performance Optimization: Short-circuit string match before expensive OS filesystem calls
+           if (fileName !in exclude) {
+               val isLinkedDirectory = Files.isDirectory(it.toPath(), LinkOption.NOFOLLOW_LINKS)
+               if ((isLinkedDirectory || !it.isDirectory()) && !Files.isSymbolicLink(it.toPath())) {
+                  val encodedHref = if (isLinkedDirectory) { "./${fileName.urlEncodePath()}/" } else { "./${fileName.urlEncodePath()}" }
+                  val ariaLabel = "${fileName} ${if (isLinkedDirectory) { "디렉토리" } else { "파일" }}".escapeHtml()
+                  val icon = if (isLinkedDirectory) { "&#128193;" } else { "&rtrif;" }
+                  l.append("""          <li><a style="display:block; width:100%" href="${encodedHref}" aria-label="${ariaLabel}"><span aria-hidden="true">${icon}</span> ${fileName.escapeHtml()}</a></li>""")
+                  l.append('\n')
+               }
            }
         }
 
diff --git a/src/test/kotlin/html4tree/MainTest.kt b/src/test/kotlin/html4tree/MainTest.kt
index 8df27da..80d1de1 100644
--- a/src/test/kotlin/html4tree/MainTest.kt
+++ b/src/test/kotlin/html4tree/MainTest.kt
@@ -148,7 +148,7 @@ class MainTest {
         assertTrue(indexFile.exists())
         val htmlContent = indexFile.readText()
         assertTrue(htmlContent.contains("<html lang=\"ko\">"))
-        assertTrue(htmlContent.contains("<nav aria-label=\"Directory listing\">"))
+        assertTrue(htmlContent.contains("<nav aria-label=\"디렉토리 목록\">"))
         assertTrue(htmlContent.contains("<main>"))
         assertTrue(htmlContent.contains("</main>"))
         assertTrue(htmlContent.contains("aria-label=\"상위 디렉토리로 이동\""))
@@ -161,6 +161,26 @@ class MainTest {
         assertFalse(htmlContent.contains("test.ignore"))
         assertTrue(htmlContent.contains("Content-Security-Policy"))
         assertTrue(htmlContent.contains("default-src 'none'; style-src 'unsafe-inline';"))
+        assertTrue(htmlContent.contains("max-width: 800px;"))
+        assertTrue(htmlContent.contains("@media (prefers-color-scheme: dark)"))
+    }
+
+    @Test
+    fun testWriteIndexFileCleansUpTempFileOnFailure() {
+        // Files.move cannot replace a non-empty directory, so this drives the
+        // exception path through write_index_file's finally block.
+        val indexDir = File(tempDir, "index.html")
+        indexDir.mkdir()
+        File(indexDir, "occupant.txt").writeText("keep")
+
+        assertFailsWith<Exception> {
+            write_index_file(tempDir, "content")
+        }
+
+        assertTrue(indexDir.isDirectory)
+        assertEquals("keep", File(indexDir, "occupant.txt").readText())
+        val leftoverTemp = tempDir.listFiles()?.filter { it.name.startsWith(".index-") } ?: emptyList()
+        assertTrue(leftoverTemp.isEmpty(), "temporary index file should be cleaned up on failure")
     }
 
     @Test
diff --git a/src/test/kotlin/html4tree/UtilTest.kt b/src/test/kotlin/html4tree/UtilTest.kt
index 81e4957..43fea2b 100644
--- a/src/test/kotlin/html4tree/UtilTest.kt
+++ b/src/test/kotlin/html4tree/UtilTest.kt
@@ -3,6 +3,7 @@ package html4tree
 import org.junit.Test
 import java.io.File
 import kotlin.test.assertEquals
+import kotlin.test.assertNotEquals
 import kotlin.test.assertNull
 
 class UtilTest {
@@ -44,6 +45,29 @@ class UtilTest {
         assertEquals("Entry(data=file1, level=0, next=null)", entry1.toString())
     }
 
+    @Test
+    fun testEntryDataClassGeneratedMembers() {
+        val file1 = File("file1")
+        val entry = Entry(file1, 0, null)
+
+        assertEquals(entry, entry)
+        assertEquals(Entry(file1, 0, null).hashCode(), entry.hashCode())
+        assertNotEquals<Any>(entry, "not an entry")
+        assertNotEquals(entry, Entry(File("file2"), 0, null))
+        assertNotEquals(entry, Entry(file1, 1, null))
+        assertNotEquals(entry, Entry(file1, 0, Entry(file1, 1, null)))
+
+        val copied = entry.copy(level = 2)
+        assertEquals(file1, copied.data)
+        assertEquals(2, copied.level)
+        assertNull(copied.next)
+
+        val (data, level, next) = entry
+        assertEquals(file1, data)
+        assertEquals(0, level)
+        assertNull(next)
+    }
+
     @Test
     fun testLinkedListEntryDataClass() {
         val file1 = File("file1")
@@ -54,6 +78,26 @@ class UtilTest {
         assertEquals("LinkedListEntry(file=file1, level=0)", entry1.toString())
     }
 
+    @Test
+    fun testLinkedListEntryDataClassGeneratedMembers() {
+        val file1 = File("file1")
+        val entry = LinkedListEntry(file1, 0)
+
+        assertEquals(entry, entry)
+        assertEquals(LinkedListEntry(file1, 0).hashCode(), entry.hashCode())
+        assertNotEquals<Any>(entry, "not an entry")
+        assertNotEquals(entry, LinkedListEntry(File("file2"), 0))
+        assertNotEquals(entry, LinkedListEntry(file1, 1))
+
+        val copied = entry.copy(level = 5)
+        assertEquals(file1, copied.file)
+        assertEquals(5, copied.level)
+
+        val (file, level) = entry
+        assertEquals(file1, file)
+        assertEquals(0, level)
+    }
+
     @Test
     fun testLinkedListPushExisting() {
         val list = LinkedList()