chore: adopt Dart 3.9 toolchain — honest floor + tall-style reformat (T-353)

Raise the declared minimums in pubspec.yaml to what our deps already
require: Flutter >=3.35.0 / Dart >=3.9.0 (was 3.19.0 / 3.5.0). alchemist
0.12 needs Flutter 3.32; Dart 3.9 first ships in Flutter 3.35, so 3.35 is
the binding floor. Pin the exact build toolchain in .fvmrc (Flutter
3.44.1).

Moving to the Dart 3.9 language level switches `dart format` to the new
"tall" style and enables two new lints. This commit is the resulting
mechanical churn, isolated from any behaviour change:
  - whole-tree `dart format` reformat (tall style)
  - `dart fix` for unnecessary_underscores + use_null_aware_elements

No runtime behaviour change; `make test` green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/src/search/grep_engine.dart

@@ -69,9 +69,7 @@ Stream<List<SearchMatch>> grepWorkspace({
   final rootPath = root.absolute.path;
 
   // Launch every chunk concurrently; await in chunk order to stream.
-  final futures = <Future<List<SearchMatch>>>[
-    for (final c in chunks) _runChunk(rootPath, c, query, maxPerFile, useIsolates),
-  ];
+  final futures = <Future<List<SearchMatch>>>[for (final c in chunks) _runChunk(rootPath, c, query, maxPerFile, useIsolates)];
 
   var emitted = 0;
   for (final f in futures) {
@@ -104,13 +102,7 @@ void _drain(List<Future<List<SearchMatch>>> futures) {
   }
 }
 
-Future<List<SearchMatch>> _runChunk(
-  String rootPath,
-  List<String> paths,
-  SearchQuery query,
-  int maxPerFile,
-  bool useIsolates,
-) {
+Future<List<SearchMatch>> _runChunk(String rootPath, List<String> paths, SearchQuery query, int maxPerFile, bool useIsolates) {
   if (useIsolates) {
     return Isolate.run(() => grepChunk(rootPath, paths, query, maxPerFile));
   }
@@ -133,12 +125,7 @@ List<List<String>> _chunk(List<String> items, int buckets) {
 /// Grep a chunk of files. Runs in a worker isolate (or in-process for
 /// tests). Reads each file, skips binaries, and collects up to
 /// [maxPerFile] matches per file.
-List<SearchMatch> grepChunk(
-  String rootPath,
-  List<String> relPaths,
-  SearchQuery query,
-  int maxPerFile,
-) {
+List<SearchMatch> grepChunk(String rootPath, List<String> relPaths, SearchQuery query, int maxPerFile) {
   final compiled = CompiledQuery(query);
   final out = <SearchMatch>[];
   for (final rel in relPaths) {
@@ -160,25 +147,13 @@ List<SearchMatch> grepChunk(
 
 /// Match [content]'s lines, appending up to [maxPerFile] hits to [out].
 /// Exposed (with a pre-built [compiled]) for unit testing without I/O.
-void grepContent(
-  String relPath,
-  String content,
-  CompiledQuery compiled,
-  int maxPerFile,
-  List<SearchMatch> out,
-) {
+void grepContent(String relPath, String content, CompiledQuery compiled, int maxPerFile, List<SearchMatch> out) {
   var lineNo = 0;
   final added0 = out.length;
   for (final line in const LineSplitter().convert(content)) {
     lineNo++;
     for (final span in compiled.matches(line)) {
-      out.add(SearchMatch(
-        path: relPath,
-        line: lineNo,
-        matchStart: span.$1,
-        matchEnd: span.$2,
-        preview: line.length > 500 ? line.substring(0, 500) : line,
-      ));
+      out.add(SearchMatch(path: relPath, line: lineNo, matchStart: span.$1, matchEnd: span.$2, preview: line.length > 500 ? line.substring(0, 500) : line));
       if (out.length - added0 >= maxPerFile) return;
     }
   }
@@ -188,9 +163,9 @@ void grepContent(
 /// matcher with an optional case-insensitive fast-path.
 class CompiledQuery {
   CompiledQuery(SearchQuery q)
-      : _regex = q.regex ? RegExp(q.pattern, caseSensitive: !q.ignoreCase) : null,
-        _needle = q.regex ? '' : (q.ignoreCase ? q.pattern.toLowerCase() : q.pattern),
-        _ignoreCase = q.ignoreCase;
+    : _regex = q.regex ? RegExp(q.pattern, caseSensitive: !q.ignoreCase) : null,
+      _needle = q.regex ? '' : (q.ignoreCase ? q.pattern.toLowerCase() : q.pattern),
+      _ignoreCase = q.ignoreCase;
 
   final RegExp? _regex;
   final String _needle;

lib/src/search/match.dart

@@ -9,13 +9,7 @@ library;
 /// result, navigate to the line, and (for replace, T-53) address the
 /// matched span within the line.
 class SearchMatch {
-  const SearchMatch({
-    required this.path,
-    required this.line,
-    required this.matchStart,
-    required this.matchEnd,
-    required this.preview,
-  });
+  const SearchMatch({required this.path, required this.line, required this.matchStart, required this.matchEnd, required this.preview});
 
   /// Repo-relative, forward-slashed path of the file.
   final String path;
@@ -32,32 +26,20 @@ class SearchMatch {
   /// The matched line's text (capped for transport/render).
   final String preview;
 
-  Map<String, Object?> toJson() => {
-        'path': path,
-        'line': line,
-        'matchStart': matchStart,
-        'matchEnd': matchEnd,
-        'preview': preview,
-      };
+  Map<String, Object?> toJson() => {'path': path, 'line': line, 'matchStart': matchStart, 'matchEnd': matchEnd, 'preview': preview};
 
   factory SearchMatch.fromJson(Map<String, Object?> j) => SearchMatch(
-        path: j['path'] as String,
-        line: (j['line'] as num).toInt(),
-        matchStart: (j['matchStart'] as num).toInt(),
-        matchEnd: (j['matchEnd'] as num).toInt(),
-        preview: j['preview'] as String,
-      );
+    path: j['path'] as String,
+    line: (j['line'] as num).toInt(),
+    matchStart: (j['matchStart'] as num).toInt(),
+    matchEnd: (j['matchEnd'] as num).toInt(),
+    preview: j['preview'] as String,
+  );
 }
 
 /// Parameters for a workspace search.
 class SearchQuery {
-  const SearchQuery({
-    required this.pattern,
-    this.regex = false,
-    this.ignoreCase = false,
-    this.include = const [],
-    this.exclude = const [],
-  });
+  const SearchQuery({required this.pattern, this.regex = false, this.ignoreCase = false, this.include = const [], this.exclude = const []});
 
   /// The literal text (when [regex] is false) or regular expression
   /// source (when true) to search for.
@@ -71,21 +53,15 @@ class SearchQuery {
   /// Glob patterns; matching paths are skipped (applied after [include]).
   final List<String> exclude;
 
-  Map<String, Object?> toJson() => {
-        'pattern': pattern,
-        'regex': regex,
-        'ignoreCase': ignoreCase,
-        'include': include,
-        'exclude': exclude,
-      };
+  Map<String, Object?> toJson() => {'pattern': pattern, 'regex': regex, 'ignoreCase': ignoreCase, 'include': include, 'exclude': exclude};
 
   factory SearchQuery.fromJson(Map<String, Object?> j) => SearchQuery(
-        pattern: (j['pattern'] as String?) ?? '',
-        regex: j['regex'] == true,
-        ignoreCase: j['ignoreCase'] == true,
-        include: _strings(j['include']),
-        exclude: _strings(j['exclude']),
-      );
+    pattern: (j['pattern'] as String?) ?? '',
+    regex: j['regex'] == true,
+    ignoreCase: j['ignoreCase'] == true,
+    include: _strings(j['include']),
+    exclude: _strings(j['exclude']),
+  );
 
   static List<String> _strings(Object? v) => v is List ? [for (final e in v) '$e'] : const [];
 }

lib/src/search/replace_engine.dart

@@ -28,11 +28,8 @@ class ReplacementEdit {
 
   Map<String, Object?> toJson() => {'line': line, 'before': before, 'after': after};
 
-  factory ReplacementEdit.fromJson(Map<String, Object?> j) => ReplacementEdit(
-        line: (j['line'] as num).toInt(),
-        before: j['before'] as String,
-        after: j['after'] as String,
-      );
+  factory ReplacementEdit.fromJson(Map<String, Object?> j) =>
+      ReplacementEdit(line: (j['line'] as num).toInt(), before: j['before'] as String, after: j['after'] as String);
 }
 
 /// The set of edits a replacement would make to one file.
@@ -46,18 +43,16 @@ class FileReplacement {
   final List<ReplacementEdit> edits;
 
   Map<String, Object?> toJson() => {
-        'path': path,
-        'count': count,
-        'edits': [for (final e in edits) e.toJson()],
-      };
+    'path': path,
+    'count': count,
+    'edits': [for (final e in edits) e.toJson()],
+  };
 
   factory FileReplacement.fromJson(Map<String, Object?> j) => FileReplacement(
-        path: j['path'] as String,
-        count: (j['count'] as num).toInt(),
-        edits: [
-          for (final e in (j['edits'] as List? ?? const []).whereType<Map>()) ReplacementEdit.fromJson(e.cast<String, Object?>()),
-        ],
-      );
+    path: j['path'] as String,
+    count: (j['count'] as num).toInt(),
+    edits: [for (final e in (j['edits'] as List? ?? const []).whereType<Map>()) ReplacementEdit.fromJson(e.cast<String, Object?>())],
+  );
 }
 
 /// Apply [query]'s pattern to [text], substituting [replacement]. Returns