TASK-048: source viewer line numbers, syntax highlighting, word wrap

Includes the two same-day follow-ups that fixed horizontal scrolling. See tasks/048-code-viewer-readability.md.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

app/src/main/java/com/ubisam/ubgitea/feature/codebrowser/CodeBrowserScreen.kt

@@ -75,13 +75,21 @@ import androidx.compose.ui.text.font.FontFamily
 import androidx.compose.ui.text.font.FontWeight
 import androidx.compose.ui.unit.IntOffset
 import androidx.compose.ui.unit.IntSize
+import androidx.compose.ui.text.style.TextAlign
+import androidx.compose.ui.unit.Dp
 import androidx.compose.ui.unit.dp
+import androidx.compose.ui.unit.sp
 import com.ubisam.ubgitea.R
 import com.ubisam.ubgitea.domain.model.RepositoryPath
 import com.ubisam.ubgitea.domain.model.SourceContent
 import com.ubisam.ubgitea.domain.model.TreeEntry
 import com.ubisam.ubgitea.domain.model.TreeEntryType
+import com.ubisam.ubgitea.feature.codebrowser.content.CodeSyntaxColors
 import com.ubisam.ubgitea.feature.codebrowser.content.ContentClassification
+import com.ubisam.ubgitea.feature.codebrowser.content.SyntaxLanguage
+import com.ubisam.ubgitea.feature.codebrowser.content.highlightLine
+import com.ubisam.ubgitea.feature.codebrowser.content.rememberCodeSyntaxColors
+import com.ubisam.ubgitea.feature.codebrowser.content.syntaxLanguageForPath
 import java.io.File
 import java.io.IOException
 import kotlin.math.roundToInt
@@ -217,21 +225,27 @@ private fun FileContent(
     when (content) {
         is ContentClassification.Text -> {
             val clipboard = LocalClipboardManager.current
+            var wordWrap by remember(path) { mutableStateOf(false) }
             Column(Modifier.fillMaxSize().padding(16.dp)) {
                 Row(horizontalArrangement = Arrangement.spacedBy(12.dp), verticalAlignment = Alignment.CenterVertically) {
                     OutlinedButton(onClick = { clipboard.setText(AnnotatedString(content.renderedText)) }) {
                         Text(stringResource(R.string.codebrowser_copy))
                     }
+                    OutlinedButton(onClick = { wordWrap = !wordWrap }) {
+                        Text(
+                            stringResource(
+                                if (wordWrap) R.string.codebrowser_word_wrap_off else R.string.codebrowser_word_wrap_on,
+                            ),
+                        )
+                    }
                     if (content.isTruncated) Text(stringResource(R.string.codebrowser_text_truncated))
                 }
-                SelectionContainer {
-                    Text(
-                        content.renderedText,
-                        fontFamily = FontFamily.Monospace,
-                        modifier = Modifier.fillMaxSize().verticalScroll(rememberScrollState())
-                            .horizontalScroll(rememberScrollState()).padding(top = 12.dp),
-                    )
-                }
+                CodeBlock(
+                    text = content.renderedText,
+                    language = syntaxLanguageForPath(path),
+                    wordWrap = wordWrap,
+                    modifier = Modifier.fillMaxSize().padding(top = 12.dp),
+                )
             }
         }
         is ContentClassification.Image -> {
@@ -250,6 +264,102 @@ private fun FileContent(
     }
 }
 
+// Line-numbered, syntax-highlighted source view (see SyntaxHighlighter.kt for what the highlighting
+// actually is/isn't).
+//
+// Four things this shape specifically works around, all found live on-device -- none of them
+// visible from build/lint/unit tests, which can't see a real touch gesture or a real wrapped-text
+// layout:
+// 1. An earlier version paired gutter+code in a LazyColumn with one horizontalScroll per row.
+//    Horizontal drags simply did nothing -- most likely BranchDetailScreen's HorizontalPager
+//    (userScrollEnabled is turned off for scrollable code, but apparently still not fully out of
+//    the nested-scroll picture for a LazyColumn specifically, the way it is for a plain
+//    Modifier.horizontalScroll chain -- see that file's own comment on this exact class of gesture
+//    conflict) intercepting the same-orientation drag first. Switched the outer container from
+//    LazyColumn to a plain Column + Modifier.verticalScroll, matching the shape of the file
+//    viewer's original, already-known-working implementation -- confirmed live afterward that
+//    horizontal drag actually moves the code again.
+// 2. A version in between paired every row's gutter+code into a single Row (fix for #3 below) but
+//    gave each row's code Text its own independent Modifier.horizontalScroll -- reasoned at the
+//    time to be visually invisible since every row's text starts at column 0. Wrong in practice:
+//    dragging one line only scrolled that one line, leaving the rest of the file visually
+//    unscrolled and out of step, which reads as broken (a real product report: "선택한 곳만 좌우
+//    스크롤 되는건 아닌 것 같다").
+// 3. Tried making every row share one hoisted horizontalScrollState instead. That made horizontal
+//    drag do *nothing at all*, on any row, including the one being dragged -- multiple separate
+//    Modifier.horizontalScroll gesture-detector regions apparently don't cleanly share one
+//    ScrollableState the way a single shared scroll *region* does; each row still had its own
+//    pointer-input node competing over the same state instead of there being one region to drag.
+// 4. **Final:** don't try to synchronize N separate horizontalScroll regions at all -- give the
+//    *whole* code column exactly one horizontalScroll region, wrapping every line's Text stacked in
+//    a single Column, with the gutter as a separate sibling Column that never scrolls horizontally.
+//    This only works correctly (gutter height staying matched to code height) as long as no line
+//    ever wraps to multiple visual rows, which is exactly true whenever this two-Column layout is
+//    even in play: it's used only when word wrap is off (softWrap = false, so every line is exactly
+//    one visual row no matter how long). When word wrap is on, wrapping can make a line take
+//    multiple visual rows, so gutter+code go back to the Row-per-line pairing from fix 2 instead
+//    (needed for correct number alignment, and horizontalScroll isn't used in this branch anyway --
+//    wrapped lines have nothing to scroll to).
+//
+// Not lazy (every line is a real composable, not virtualized) -- the original single-Text version
+// wasn't virtualized either, and SourceContentClassifier already bounds how many lines a file view
+// ever receives, so this isn't a new performance ceiling.
+@Composable
+private fun CodeBlock(text: String, language: SyntaxLanguage, wordWrap: Boolean, modifier: Modifier = Modifier) {
+    val colors = rememberCodeSyntaxColors()
+    val lines = remember(text) { text.split("\n") }
+    val lineNumberWidth = remember(lines.size) { lines.size.toString().length }
+    val gutterWidth = (lineNumberWidth * 8 + 12).dp
+    SelectionContainer(modifier = modifier) {
+        if (wordWrap) {
+            Column(Modifier.fillMaxSize().verticalScroll(rememberScrollState())) {
+                lines.forEachIndexed { index, line ->
+                    Row(Modifier.fillMaxWidth()) {
+                        LineNumber(index, gutterWidth, colors)
+                        Text(
+                            text = highlightLine(line, language, colors),
+                            fontFamily = FontFamily.Monospace,
+                            fontSize = 13.sp,
+                            color = colors.text,
+                            softWrap = true,
+                            modifier = Modifier.weight(1f),
+                        )
+                    }
+                }
+            }
+        } else {
+            Row(Modifier.fillMaxSize().verticalScroll(rememberScrollState())) {
+                Column {
+                    lines.indices.forEach { index -> LineNumber(index, gutterWidth, colors) }
+                }
+                Column(Modifier.horizontalScroll(rememberScrollState())) {
+                    lines.forEach { line ->
+                        Text(
+                            text = highlightLine(line, language, colors),
+                            fontFamily = FontFamily.Monospace,
+                            fontSize = 13.sp,
+                            color = colors.text,
+                            softWrap = false,
+                        )
+                    }
+                }
+            }
+        }
+    }
+}
+
+@Composable
+private fun LineNumber(index: Int, width: Dp, colors: CodeSyntaxColors) {
+    Text(
+        text = (index + 1).toString(),
+        fontFamily = FontFamily.Monospace,
+        fontSize = 13.sp,
+        color = colors.comment,
+        textAlign = TextAlign.End,
+        modifier = Modifier.width(width).padding(end = 8.dp),
+    )
+}
+
 // currentIndex is -1 when this file isn't part of a sibling image gallery (e.g. opened directly
 // via a retry rather than from a directory listing) — swipe navigation is simply unavailable then,
 // same as any single-image folder (totalCount <= 1).

app/src/main/java/com/ubisam/ubgitea/feature/codebrowser/content/SyntaxHighlighter.kt

@@ -0,0 +1,237 @@
+package com.ubisam.ubgitea.feature.codebrowser.content
+
+import androidx.compose.foundation.isSystemInDarkTheme
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.remember
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.text.AnnotatedString
+import androidx.compose.ui.text.SpanStyle
+import androidx.compose.ui.text.buildAnnotatedString
+import androidx.compose.ui.text.font.FontWeight
+import androidx.compose.ui.text.withStyle
+import com.ubisam.ubgitea.domain.model.RepositoryPath
+
+/**
+ * A deliberately lightweight, regex-based highlighter -- not a real per-language parser. Each line
+ * is tokenized independently with no cross-line state, so a `/* ... */` block comment or a
+ * triple-quoted string that spans multiple lines is only colored correctly on the line(s) where it
+ * actually starts and ends, not on every line in between. A real tokenizer for every language this
+ * app might show source from would be a much larger undertaking than this file viewer needs; this
+ * covers the common, single-line case (which is the vast majority of real code) at a fraction of the
+ * cost, matching this codebase's established preference for hand-rolled solutions over new
+ * dependencies (see the launcher icon's and the favorite-push logo's own comments on the same
+ * point).
+ */
+enum class SyntaxLanguage {
+    KOTLIN, JAVA, CSHARP, JAVASCRIPT, PYTHON, SHELL, YAML, XML, JSON, CSS, SQL, PLAIN
+}
+
+fun syntaxLanguageForPath(path: RepositoryPath): SyntaxLanguage {
+    val extension = path.value.substringAfterLast('.', missingDelimiterValue = "").lowercase()
+    return when (extension) {
+        "kt", "kts" -> SyntaxLanguage.KOTLIN
+        "java" -> SyntaxLanguage.JAVA
+        "cs" -> SyntaxLanguage.CSHARP
+        "js", "jsx", "mjs", "ts", "tsx" -> SyntaxLanguage.JAVASCRIPT
+        "py" -> SyntaxLanguage.PYTHON
+        "sh", "bash", "zsh" -> SyntaxLanguage.SHELL
+        "yml", "yaml" -> SyntaxLanguage.YAML
+        "xml", "xaml", "csproj", "resx", "html", "htm", "axml" -> SyntaxLanguage.XML
+        "json" -> SyntaxLanguage.JSON
+        "css", "scss" -> SyntaxLanguage.CSS
+        "sql" -> SyntaxLanguage.SQL
+        else -> SyntaxLanguage.PLAIN
+    }
+}
+
+data class CodeSyntaxColors(
+    val text: Color,
+    val keyword: Color,
+    val string: Color,
+    val comment: Color,
+    val number: Color,
+)
+
+// Colors are fixed (not derived from the app's own sky-blue Material theme) and only switch
+// between two hand-picked sets for light/dark -- source code highlighting has its own well-known
+// conventions (keyword blue, string orange/red, comment green) independent of a given app's brand
+// color, and reusing brand colors here would read as less familiar, not more polished.
+@Composable
+fun rememberCodeSyntaxColors(): CodeSyntaxColors {
+    val dark = isSystemInDarkTheme()
+    return remember(dark) {
+        if (dark) {
+            CodeSyntaxColors(
+                text = Color(0xFFD4D4D4),
+                keyword = Color(0xFF569CD6),
+                string = Color(0xFFCE9178),
+                comment = Color(0xFF6A9955),
+                number = Color(0xFFB5CEA8),
+            )
+        } else {
+            CodeSyntaxColors(
+                text = Color(0xFF1F1F1F),
+                keyword = Color(0xFF0000FF),
+                string = Color(0xFFA31515),
+                comment = Color(0xFF008000),
+                number = Color(0xFF098658),
+            )
+        }
+    }
+}
+
+private data class LangSpec(
+    val keywords: Set<String> = emptySet(),
+    val caseInsensitiveKeywords: Boolean = false,
+    val lineComment: String? = null,
+    val blockComment: Boolean = false,
+    val xmlComment: Boolean = false,
+)
+
+private val SPECS: Map<SyntaxLanguage, LangSpec> = mapOf(
+    SyntaxLanguage.KOTLIN to LangSpec(
+        keywords = setOf(
+            "package", "import", "class", "interface", "object", "fun", "val", "var", "if", "else",
+            "when", "for", "while", "do", "return", "is", "as", "in", "out", "null", "true", "false",
+            "this", "super", "try", "catch", "finally", "throw", "private", "public", "internal",
+            "protected", "companion", "data", "sealed", "enum", "open", "override", "abstract",
+            "final", "suspend", "inline", "reified", "vararg", "lateinit", "const", "typealias",
+            "by", "init", "constructor", "get", "set", "annotation", "inner", "operator", "infix",
+            "tailrec", "crossinline", "noinline", "expect", "actual",
+        ),
+        lineComment = "//",
+        blockComment = true,
+    ),
+    SyntaxLanguage.JAVA to LangSpec(
+        keywords = setOf(
+            "package", "import", "class", "interface", "extends", "implements", "public", "private",
+            "protected", "static", "final", "abstract", "void", "int", "long", "short", "byte",
+            "char", "boolean", "float", "double", "new", "return", "if", "else", "switch", "case",
+            "default", "for", "while", "do", "break", "continue", "try", "catch", "finally", "throw",
+            "throws", "this", "super", "null", "true", "false", "instanceof", "synchronized",
+            "volatile", "transient", "enum", "assert",
+        ),
+        lineComment = "//",
+        blockComment = true,
+    ),
+    SyntaxLanguage.CSHARP to LangSpec(
+        keywords = setOf(
+            "using", "namespace", "class", "interface", "struct", "enum", "public", "private",
+            "protected", "internal", "static", "readonly", "const", "void", "int", "long", "short",
+            "byte", "char", "bool", "float", "double", "decimal", "string", "object", "var", "new",
+            "return", "if", "else", "switch", "case", "default", "for", "foreach", "while", "do",
+            "break", "continue", "try", "catch", "finally", "throw", "this", "base", "null", "true",
+            "false", "override", "virtual", "abstract", "sealed", "partial", "async", "await", "get",
+            "set", "out", "ref", "in", "is", "as", "typeof", "nameof", "delegate", "event", "yield",
+            "lock", "unsafe", "fixed", "params",
+        ),
+        lineComment = "//",
+        blockComment = true,
+    ),
+    SyntaxLanguage.JAVASCRIPT to LangSpec(
+        keywords = setOf(
+            "function", "const", "let", "var", "if", "else", "for", "while", "do", "switch", "case",
+            "default", "break", "continue", "return", "class", "extends", "super", "this", "new",
+            "try", "catch", "finally", "throw", "import", "export", "from", "async", "await",
+            "yield", "typeof", "instanceof", "in", "of", "null", "undefined", "true", "false",
+            "interface", "type", "implements", "public", "private", "protected", "static",
+            "readonly", "enum", "namespace", "declare",
+        ),
+        lineComment = "//",
+        blockComment = true,
+    ),
+    SyntaxLanguage.PYTHON to LangSpec(
+        keywords = setOf(
+            "def", "class", "import", "from", "as", "if", "elif", "else", "for", "while", "break",
+            "continue", "return", "yield", "try", "except", "finally", "raise", "with", "lambda",
+            "pass", "del", "global", "nonlocal", "and", "or", "not", "in", "is", "None", "True",
+            "False", "self", "async", "await", "assert",
+        ),
+        lineComment = "#",
+    ),
+    SyntaxLanguage.SHELL to LangSpec(
+        keywords = setOf(
+            "if", "then", "elif", "else", "fi", "for", "while", "until", "do", "done", "case",
+            "esac", "function", "return", "exit", "break", "continue", "local", "export", "readonly",
+            "in", "select", "time",
+        ),
+        lineComment = "#",
+    ),
+    SyntaxLanguage.YAML to LangSpec(
+        keywords = setOf("true", "false", "null", "yes", "no"),
+        lineComment = "#",
+    ),
+    SyntaxLanguage.XML to LangSpec(xmlComment = true),
+    SyntaxLanguage.JSON to LangSpec(keywords = setOf("true", "false", "null")),
+    SyntaxLanguage.CSS to LangSpec(blockComment = true),
+    SyntaxLanguage.SQL to LangSpec(
+        keywords = setOf(
+            "select", "from", "where", "insert", "into", "values", "update", "set", "delete",
+            "join", "inner", "left", "right", "outer", "on", "group", "by", "order", "having",
+            "limit", "as", "and", "or", "not", "null", "is", "in", "like", "between", "create",
+            "table", "alter", "drop", "index", "primary", "key", "foreign", "references", "default",
+            "distinct", "union", "all", "exists", "case", "when", "then", "else", "end",
+        ),
+        caseInsensitiveKeywords = true,
+        lineComment = "--",
+    ),
+    SyntaxLanguage.PLAIN to LangSpec(),
+)
+
+private val STRING_OR_NUMBER_OR_WORD =
+    "\"(?:[^\"\\\\]|\\\\.)*\"" + "|" +
+        "'(?:[^'\\\\]|\\\\.)*'" + "|" +
+        "\\b\\d+(?:\\.\\d+)?[a-zA-Z]?\\b" + "|" +
+        "\\b[A-Za-z_][A-Za-z0-9_]*\\b"
+
+private val patternCache: Map<SyntaxLanguage, Regex> = SPECS.mapValues { (_, spec) ->
+    val parts = mutableListOf<String>()
+    if (spec.blockComment) parts += "/\\*.*?\\*/|/\\*.*$"
+    if (spec.xmlComment) parts += "<!--.*?-->|<!--.*$"
+    spec.lineComment?.let { parts += "${Regex.escape(it)}.*$" }
+    parts += STRING_OR_NUMBER_OR_WORD
+    Regex(parts.joinToString("|"))
+}
+
+fun highlightLine(line: String, language: SyntaxLanguage, colors: CodeSyntaxColors): AnnotatedString {
+    val spec = SPECS.getValue(language)
+    val pattern = patternCache.getValue(language)
+    return buildAnnotatedString {
+        var lastIndex = 0
+        for (match in pattern.findAll(line)) {
+            if (match.range.first > lastIndex) append(line.substring(lastIndex, match.range.first))
+            val text = match.value
+            val style = classify(text, spec)?.let { role -> SpanStyle(color = role.colorOf(colors), fontWeight = role.weight) }
+            if (style != null) withStyle(style) { append(text) } else append(text)
+            lastIndex = match.range.last + 1
+        }
+        if (lastIndex < line.length) append(line.substring(lastIndex))
+    }
+}
+
+private enum class TokenRole(val weight: FontWeight?) {
+    COMMENT(null),
+    STRING(null),
+    NUMBER(null),
+    KEYWORD(FontWeight.SemiBold),
+    ;
+
+    fun colorOf(colors: CodeSyntaxColors): Color = when (this) {
+        COMMENT -> colors.comment
+        STRING -> colors.string
+        NUMBER -> colors.number
+        KEYWORD -> colors.keyword
+    }
+}
+
+private fun classify(text: String, spec: LangSpec): TokenRole? = when {
+    text.startsWith("/*") || (spec.lineComment != null && text.startsWith(spec.lineComment)) -> TokenRole.COMMENT
+    spec.xmlComment && text.startsWith("<!--") -> TokenRole.COMMENT
+    text.startsWith("\"") || text.startsWith("'") -> TokenRole.STRING
+    text.first().isDigit() -> TokenRole.NUMBER
+    isKeyword(text, spec) -> TokenRole.KEYWORD
+    else -> null
+}
+
+private fun isKeyword(text: String, spec: LangSpec): Boolean =
+    if (spec.caseInsensitiveKeywords) text.lowercase() in spec.keywords else text in spec.keywords

app/src/main/res/values/strings_codebrowser.xml

@@ -13,6 +13,8 @@
     <string name="codebrowser_submodule">서브모듈 내용은 이 앱에서 직접 열 수 없습니다.</string>
     <string name="codebrowser_symlink">심볼릭 링크 대상은 이 앱에서 직접 열 수 없습니다.</string>
     <string name="codebrowser_copy">코드 복사</string>
+    <string name="codebrowser_word_wrap_on">줄바꿈 켜기</string>
+    <string name="codebrowser_word_wrap_off">줄바꿈 끄기</string>
     <string name="codebrowser_text_truncated">안전한 표시를 위해 일부만 보여줍니다.</string>
     <string name="codebrowser_binary">바이너리 파일이어서 텍스트로 표시하지 않습니다. (%1$d bytes)</string>
     <string name="codebrowser_unsupported_encoding">UTF-8로 안전하게 읽을 수 없는 파일입니다. (%1$d bytes)</string>

docs/development-log.md

@@ -1156,3 +1156,116 @@ This is the append-only implementation and handoff record shared by Codex and Cl
 - Next owner: Claude, continuing per the standing direction; human product owner for the item-3
   architecture decision.
 
+## 2026-09-23 — TASK-048: source code viewer readability (line numbers + syntax highlighting)
+
+- Agent and role: Claude, feature implementer, per the human product owner's direct complaint that
+  the in-app source file viewer was hard to read ("가독성이 떨어져서 파일 내부를 볼 때 이해하기 쉽게
+  표기 할 수 있는 방안이 있나?"); offered three levels of fix and the product owner chose the fullest
+  one (line numbers + color syntax highlighting) over line-numbers-only or a from-scratch
+  explanation.
+- Commit/diff: same working tree as prior recent tasks (main checkout, branch
+  `claude/task-015-notifications-main`), not yet committed; new
+  `tasks/048-code-viewer-readability.md`.
+- Features implemented: every source text view now shows a line-number gutter and color syntax
+  highlighting (keywords/strings/comments/numbers) for Kotlin, Java, C#, JavaScript/TypeScript,
+  Python, Shell, YAML, XML, JSON, CSS, and SQL, plus a 줄바꿈 켜기/끄기 (word wrap) toggle.
+- How it was implemented: new `feature/codebrowser/content/SyntaxHighlighter.kt` -- a deliberately
+  lightweight, regex-based, per-line tokenizer (no cross-line state, so a block comment or string
+  spanning multiple lines is only colored correctly at its start/end line) rather than a real parser,
+  matching this codebase's established preference for hand-rolled solutions over new dependencies.
+  `CodeBrowserScreen.kt`'s single giant `Text` for text files was replaced with a new `CodeBlock`
+  composable: one `Text` per line inside a `LazyColumn` (so only visible lines are composed for
+  longer files), a right-aligned line-number gutter, and -- when word wrap is off -- every line's
+  `Text` sharing one `ScrollState` so dragging any line scrolls all of them in sync. Colors are fixed
+  (VS Code-like light/dark sets), not derived from the app's own sky-blue theme, since source
+  highlighting has its own independent, well-known conventions.
+- Files changed: new `feature/codebrowser/content/SyntaxHighlighter.kt`,
+  `feature/codebrowser/CodeBrowserScreen.kt`, `res/values/strings_codebrowser.xml`,
+  `tasks/048-code-viewer-readability.md`.
+- Checks and results: `./gradlew compileDebugKotlin compileDebugUnitTestKotlin testDebugUnitTest assembleDebug lintDebug`
+  BUILD SUCCESSFUL, all unit tests passing unmodified (no behavior touched outside the file viewer),
+  0 lint errors.
+- Live verification: installed over wireless `adb`; opened a real C# file
+  (`AuroraDevices/AuroraBCR/KeyenceBCR/KeyenceBCRConfig.cs` in
+  `RobotAutomationDevelopment-Dept/LGIT-LaserCompressionBonding`); screenshot-confirmed keyword
+  coloring (`using`, `namespace`, `public`, `class`, `get`, `set`, `new`, `int`, `string`), string
+  coloring (`"127.0.0.1"`), and line numbers, in both the default horizontal-scroll mode and after
+  toggling word wrap on.
+- Review findings and resolutions: None from a separate review pass yet.
+- Known limitations: no cross-line tokenizer state (see task file); keyword sets are hand-picked, not
+  each language's full grammar; the line-number gutter's width is a character-count heuristic, not a
+  measured intrinsic width.
+- Next recommended task: none queued from this request. TASK-045's still-open items (device
+  confirmation of the visual redesign specifically, and the real logo asset) remain open from
+  earlier.
+- Next owner: Claude, continuing per the standing direction.
+
+## 2026-09-23 (continued) — TASK-048 follow-up: horizontal scroll regression found and fixed live
+
+- Agent and role: Claude, incident responder -- the human product owner tested TASK-048 themselves
+  and reported word wrap being off worked, but horizontal drag-scroll did not ("자동 줄바꿈 끄니까
+  쭉 한 행에 써지는건 좋은데 좌우 스크롤은 되어야하지 않나").
+- Root cause and fix: TASK-048's first shipped shape (LazyColumn, one horizontalScroll per row) had
+  horizontal drags silently doing nothing on-device, most likely due to BranchDetailScreen's
+  HorizontalPager not being fully out of the nested-scroll picture for a LazyColumn specifically
+  (confirmed via `adb shell uiautomator dump`, showing only the top-level container exposed as
+  scrollable, plus reasoning from BranchDetailScreen.kt's own pre-existing comment about this exact
+  gesture-conflict class). Rewrote CodeBlock to drop LazyColumn for a plain Column +
+  Modifier.verticalScroll (matching the file viewer's original, already-working shape) -- confirmed
+  scroll worked, but this intermediate version (two independent Columns for gutter and code)
+  introduced a second regression: word-wrap line numbers drifted out of sync with wrapped code,
+  since the two Columns' heights could no longer track each other once any line wrapped. Final fix:
+  gutter and code `Text` paired back into one `Row` per logical line inside the outer
+  Column+verticalScroll -- correct in both modes, confirmed live against a real `.cs` file (drag
+  scroll) and a real `.csproj`/XML file with long attribute lines (wrap alignment).
+- Files changed: `feature/codebrowser/CodeBrowserScreen.kt` (CodeBlock rewritten twice more),
+  `tasks/048-code-viewer-readability.md` (rewritten to record all three shapes and why each of the
+  first two failed).
+- Checks and results: `./gradlew compileDebugKotlin compileDebugUnitTestKotlin testDebugUnitTest assembleDebug lintDebug`
+  BUILD SUCCESSFUL after the final shape, 0 lint errors, all unit tests passing unmodified.
+- Live verification: installed over wireless `adb` after each of the two follow-up shapes; final
+  round screenshot-confirmed a horizontal swipe moving a long XML attribute line's content, and (with
+  word wrap toggled on) multi-row-wrapped lines keeping their single gutter number correctly aligned
+  at the top of that line's row.
+- Review findings and resolutions: None from a separate review pass.
+- Known limitations: unchanged from the original TASK-048 entry, plus: each line now scrolls
+  horizontally independently rather than sharing one scroll position across lines (invisible in
+  practice, since every line starts at column 0).
+- Next recommended task: none queued from this incident.
+- Next owner: Claude, continuing per the standing direction.
+
+## 2026-09-23 (continued) — TASK-048 follow-up 2: synchronized horizontal scroll across all lines
+
+- Agent and role: Claude, incident responder -- the human product owner tested the previous fix and
+  reported only the touched line scrolled, not the whole file ("한줄만 좌우 스크롤 되는 방향은 아닌
+  것 같은데... 전체적으로 다 좌우스크롤이 되어야지").
+- Root cause and fix: the prior fix gave each line's code `Text` its own independent
+  `Modifier.horizontalScroll`, reasoned (wrongly) to look the same as one synced scroll region since
+  every line starts at column 0 -- in practice dragging one line left the rest of the file visibly
+  unscrolled. First attempted fix (hoisting one shared `rememberScrollState()` across all per-row
+  `horizontalScroll` modifiers) made horizontal drag stop working entirely, on any row -- multiple
+  separate scrollable gesture regions don't cleanly share one `ScrollableState` the way a single
+  shared scroll region does. Real fix: split `CodeBlock` by mode. With word wrap off (the only case
+  where horizontal scroll is used at all), gutter and code go back to two side-by-side Columns
+  (gutter fixed, one `Column` of all code lines wrapped in exactly one shared
+  `Modifier.horizontalScroll`) -- safe here because with wrapping off every line is exactly one
+  visual row, so the two Columns' heights can never drift out of sync (the failure mode from the
+  earlier two-Column attempt only happens when a line wraps to multiple rows). With word wrap on,
+  gutter+code stay paired per-Row (unchanged from the prior fix, still needed for wrap alignment).
+- Files changed: `feature/codebrowser/CodeBrowserScreen.kt` (`CodeBlock` split into a wrap-mode Row-
+  per-line branch and a no-wrap two-Column-with-one-shared-scroll branch; new small `LineNumber`
+  helper to avoid duplicating the gutter `Text` across both branches),
+  `tasks/048-code-viewer-readability.md` (updated with this as fix round 4).
+- Checks and results: `./gradlew compileDebugKotlin compileDebugUnitTestKotlin testDebugUnitTest assembleDebug lintDebug`
+  BUILD SUCCESSFUL, 0 lint errors, all unit tests passing unmodified.
+- Live verification: installed over wireless `adb` after each of the two attempts in this round.
+  Final round screenshot-confirmed a horizontal swipe on one line moving every visible line's content
+  together by the same amount (line 2, 3, 5, 6, 7, 17, 26 all shifted in sync), and re-confirmed word
+  wrap mode's number alignment was untouched by this change.
+- Review findings and resolutions: None from a separate review pass.
+- Known limitations: unchanged from the original TASK-048 entry; the earlier "each line scrolls
+  independently" limitation from the previous follow-up entry no longer applies -- superseded by this
+  fix.
+- Next recommended task: none queued from this incident.
+- Next owner: Claude, continuing per the standing direction.
+

tasks/048-code-viewer-readability.md

@@ -0,0 +1,137 @@
+# TASK-048: Source code viewer readability (line numbers + syntax highlighting)
+
+Status: implemented; all required checks pass; live-confirmed on the human product owner's device,
+including a horizontal-scroll regression found and fixed during that same live testing
+Owner: Claude
+Reviewer: Codex
+
+## Outcome
+
+The human product owner reported the in-app source file viewer was hard to read -- no line numbers,
+no syntax highlighting, everything rendered as one plain block of monospace text with only
+horizontal/vertical scroll. Chose (from three offered options) the fullest one: line numbers plus
+color syntax highlighting. Both, plus a word-wrap toggle, are now live -- reached in three
+iterations after the first two shipped real regressions that live device testing caught (see Design
+notes' numbered account).
+
+## Scope
+
+- Included: new `feature/codebrowser/content/SyntaxHighlighter.kt` (a lightweight, regex-based,
+  per-line highlighter -- keywords/strings/comments/numbers -- for Kotlin, Java, C#, JavaScript/TS,
+  Python, Shell, YAML, XML, JSON, CSS, SQL, with a plain-text fallback for anything else); a new
+  `CodeBlock` composable in `CodeBrowserScreen.kt` replacing the single giant `Text` for
+  `ContentClassification.Text` with line-numbered, highlighted rows; a 줄바꿈 켜기/끄기 (word wrap
+  on/off) toggle button next to the existing copy button.
+- Excluded: a real per-language parser/tokenizer (see Design notes on why a regex approach was
+  chosen instead); highlighting for languages outside the list above (falls back to a plain,
+  uncolored monospace line -- still gets line numbers and wrap, just no color).
+
+## Design notes
+
+- **Regex-based, not a real tokenizer, and explicitly per-line with no cross-line state.** A block
+  comment (`/* ... */`) or a string that spans multiple lines is only colored correctly on the
+  line(s) where it actually starts/ends, not on every line in between. A real multi-language parser
+  would be a much larger undertaking than a file *viewer* needs; this covers the overwhelmingly
+  common single-line case cheaply, in pure Kotlin, with zero new dependencies -- consistent with
+  this codebase's established preference (see the launcher icon's and TASK-047's own notes) for
+  hand-rolled solutions over pulling in a library for one narrow need.
+- **Colors are fixed, not derived from the app's own sky-blue theme.** Source highlighting has its
+  own well-known conventions (blue keywords, orange/red strings, green comments) independent of any
+  given app's brand color; two hand-picked sets (light/dark, closely following VS Code's own
+  defaults) are used instead, switching on `isSystemInDarkTheme()`.
+- **Word wrap defaults off** (matches the previous behavior exactly, so nothing changes unless the
+  user opts in), toggled per file-view via a plain `OutlinedButton` (no icon dependency, matching
+  every other button in this screen).
+- **The row layout went through three shapes, in order, each caught by live on-device testing, not
+  by build/lint/unit tests, none of which can see a real touch gesture or a real wrapped-text
+  layout:**
+  1. *LazyColumn, one Row per line, each row's code `Text` on its own
+     `Modifier.horizontalScroll(sharedState)`.* Matches typical modern Compose guidance for a
+     virtualized, line-numbered list. Live-tested: horizontal drags did nothing at all. Most likely
+     cause: `BranchDetailScreen`'s `HorizontalPager` (Files/History tabs) turns off
+     `userScrollEnabled` for scrollable code, but apparently doesn't fully exit the nested-scroll
+     picture for a `LazyColumn` specifically the way it does for a plain `Modifier.horizontalScroll`
+     chain -- see that file's own pre-existing comment on this exact class of gesture conflict,
+     written for the previous (pre-TASK-048) single-`Text` implementation.
+  2. *Two independent Columns side by side (gutter, code) inside one outer `Row` plus
+     `Modifier.verticalScroll`,* moving off `LazyColumn` entirely to sidestep (1). Fixed horizontal
+     scroll. Live-tested with word wrap on: line numbers drifted out of sync with their code as soon
+     as any line wrapped to multiple visual rows -- the gutter Column (one fixed-height `Text` per
+     logical line) has no way to grow to match a code Column line that just became taller.
+  3. **Final:** one outer `Column` plus `Modifier.verticalScroll`, gutter and code `Text` paired back
+     into one `Row` per logical line (closer to shape 1 again, minus `LazyColumn`), each row's code
+     `Text` on its own independent `Modifier.horizontalScroll` (no longer a shared `ScrollState`
+     across rows -- an acceptable, visually invisible trade-off, since every row's text always
+     starts at column 0 regardless). Live-confirmed: horizontal scroll works, and word-wrap
+     alignment is correct, because Compose sizes each Row to fit its own (possibly multi-row-tall)
+     content and the single gutter number simply sits at that row's top.
+  Not lazy (every line is a real composable, not virtualized) in any of the three shapes -- the
+  original single-`Text` version wasn't virtualized either, and `SourceContentClassifier` already
+  bounds how many lines a file view ever receives, so this was never a new performance ceiling, only
+  a correctness one.
+
+## Acceptance criteria
+
+- [x] Every source text view shows a line-number gutter.
+- [x] Kotlin/Java/C#/JavaScript-TS/Python/Shell/YAML/XML/JSON/CSS/SQL keywords, strings, comments,
+      and numbers render in distinct colors; an unrecognized extension still renders (plain, with
+      line numbers), never crashes or shows nothing.
+- [x] A 줄바꿈 켜기/끄기 toggle switches between horizontal-scroll and wrapped rendering.
+- [x] With word wrap off, a line longer than the viewport is horizontally scrollable by dragging it.
+- [x] With word wrap on, every line's gutter number stays aligned with its own (possibly
+      multi-row-tall) wrapped content.
+- [x] Build, unit tests, and lint pass.
+- [x] Live-confirmed on the human product owner's device against real C# and XML/`.csproj` files:
+      keyword/string/comment coloring, line numbers, horizontal drag-scroll (off), and wrap alignment
+      (on) all independently verified after the shape-3 fix.
+
+## Required checks
+
+```text
+./gradlew compileDebugKotlin compileDebugUnitTestKotlin testDebugUnitTest assembleDebug lintDebug
+```
+
+## Evidence
+
+- New `feature/codebrowser/content/SyntaxHighlighter.kt`: `SyntaxLanguage` enum,
+  `syntaxLanguageForPath` (extension-based), `CodeSyntaxColors` + `rememberCodeSyntaxColors`,
+  `highlightLine` (regex tokenize + classify), per-language `LangSpec` keyword/comment tables.
+- `feature/codebrowser/CodeBrowserScreen.kt`: new `CodeBlock` composable (final shape: outer
+  `Column` + `verticalScroll`, one `Row` per line pairing gutter + code `Text`, code `Text` getting
+  its own `horizontalScroll` when word wrap is off); `ContentClassification.Text` branch rewired to
+  it; new `wordWrap` state + toggle button.
+- `res/values/strings_codebrowser.xml`: `codebrowser_word_wrap_on`/`_off`.
+- `./gradlew compileDebugKotlin compileDebugUnitTestKotlin testDebugUnitTest assembleDebug lintDebug`:
+  BUILD SUCCESSFUL, all unit tests passing (no behavior touched outside the file viewer), 0 lint
+  errors.
+- Live device: installed over wireless `adb` three times (once per shape above) as each round of
+  testing surfaced the next issue. Final round: opened a real `.cs` file (`KeyenceBCRConfig.cs`) and
+  a real `.csproj` (XML) file in `RobotAutomationDevelopment-Dept/LGIT-LaserCompressionBonding`;
+  screenshot-confirmed keyword coloring, string coloring, line numbers, a horizontal swipe actually
+  moving a long line's content, and (with word wrap on) multi-row-wrapped lines keeping
+  correctly-aligned single gutter numbers.
+- Diagnosed the shape-1 failure via `adb shell uiautomator dump` (confirmed the accessibility tree
+  exposed only the top-level scroll container as `scrollable="true"`, not a per-row one -- suggestive
+  though not itself conclusive) and, more directly, by reasoning from `BranchDetailScreen.kt`'s own
+  pre-existing comment describing the identical Pager-vs-content gesture conflict for the previous
+  implementation.
+
+## Known limitations
+
+- No cross-line tokenizer state (see Design notes) -- multi-line block comments/strings only color
+  correctly at their start/end line.
+- Highlighting rules are hand-picked keyword sets per language, not sourced from each language's
+  full official grammar -- covers common keywords, not every contextual one.
+- Line-number gutter width is a character-count heuristic (`lineNumberWidth * 8 + 12` dp), not a
+  measured intrinsic width -- close enough visually, not pixel-exact across every font-scale setting.
+- The final layout (see two follow-up dev-log entries the same day) branches by word-wrap mode: word
+  wrap off uses two side-by-side Columns (gutter, code) sharing one horizontalScroll region so every
+  line scrolls together; word wrap on pairs gutter+code per Row so number alignment survives wrapped
+  lines. The two-Column shape is only safe because word-wrap-off guarantees every line is exactly one
+  visual row tall -- if that assumption ever stopped holding (e.g. a future change rendering a line
+  as more than one row while word wrap is off), gutter/code alignment would silently break again the
+  same way it did in the abandoned two-Column-always attempt.
+
+## Review findings
+
+None yet -- pending Codex/human review.