Fix RangeError in doc-imports stripping by detecting index overshoot.

Detect when absolute offsets from the analyzer overshoot the normalized string length
(due to intermediate non-doc comments like `// ignore` breaking the sequence, or \r\n line endings)
and skip stripping to avoid a crash. Added regression tests.

lib/src/model/documentation_comment.dart

diff --git a/lib/src/model/documentation_comment.dart b/lib/src/model/documentation_comment.dart
index 774284a..b76aae1 100644
--- a/lib/src/model/documentation_comment.dart
+++ b/lib/src/model/documentation_comment.dart
@@ -866,7 +866,17 @@
       var buffer = StringBuffer();
       if (commentData.docImports.isEmpty) return content;
       var firstDocImport = commentData.docImports.first;
-      buffer.write(content.substring(0, firstDocImport.offset - commentOffset));
+
+      var relativeOffset = firstDocImport.offset - commentOffset;
+      if (relativeOffset >= content.length) {
+        // Safe fallback if indices drift due to line ending normalization.
+        warn(PackageWarning.deprecated,
+            message:
+                'Index drift detected when removing doc imports. This is often caused by `// ignore` blocks or `\\r\\n` line endings in your documentation. Convert file to use `\\n` and remove intermediate non-doc comments to ensure doc imports are removed properly.');
+        return content;
+      }
+
+      buffer.write(content.substring(0, relativeOffset));
       var offset = firstDocImport.end - commentOffset;
       for (var docImport in commentData.docImports.skip(1)) {
         buffer

test/documentation_comment_test.dart

diff --git a/test/documentation_comment_test.dart b/test/documentation_comment_test.dart
index 3123358..974edbe 100644
--- a/test/documentation_comment_test.dart
+++ b/test/documentation_comment_test.dart
@@ -277,6 +277,33 @@
     expect(doc, equals(''));
   }
 
+  void test_docImport_overshoot() async {
+    // Force \r\n line endings to simulate index drift if the analyzer normalizes it to \n.
+    // We use many lines to ensure the shift overshoots the string length and throws RangeError.
+    var lines = List.generate(50, (i) => '/// Line $i').join('\n');
+    await writePackageWithCommentedLibrary('''
+$lines
+/// @docImport 'dart:async' as async;
+'''.replaceAll('\n', '\r\n'));
+    var doc = libraryModel.documentation;
+
+    // Should not crash!
+    expect(doc, isNotNull);
+  }
+
+  void test_docImport_ignoreBlock() async {
+    await writePackageWithCommentedLibrary('''
+/// Line 1
+// ignore: something
+/// Line 2
+/// @docImport 'dart:async' as async;
+''');
+    var doc = libraryModel.documentation;
+
+    // Should not crash!
+    expect(doc, isNotNull);
+  }
+
   void test_animationDirectiveHasFewerThanThreeArguments() async {
     await writePackageWithCommentedLibrary('''
 /// Text.