fix: Change LeaveStreamOpen default from true to false

AGENTS.md

@@ -126,10 +126,17 @@ SharpCompress supports multiple archive and compression formats:
 - See [docs/FORMATS.md](docs/FORMATS.md) for complete format support matrix
 
 ### Stream Handling Rules
-- **Disposal**: As of version 0.21, SharpCompress closes wrapped streams by default
-- Use `ReaderOptions` or `WriterOptions` with `LeaveStreamOpen = true` to control stream disposal
+- **Disposal semantics**: The default `ReaderOptions.LeaveStreamOpen` value is `false`, but effective stream ownership depends on which API overload you call
+  - File-based overloads (e.g., `OpenArchive(string filePath)`) open the file internally and own that stream, so it is closed by default with the archive/reader
+    - Do **not** rely on a specific `ReaderOptions` preset being used internally; some implementations may use `ReaderOptions.ForFilePath`, while others may use default `ReaderOptions` with the same ownership semantics
+  - Several high-level overloads that accept a caller-provided `Stream` use external-stream semantics by default (for example, `ReaderFactory.OpenReader(Stream)` / `ArchiveFactory.OpenArchive(Stream)`), so the caller's stream is typically left open unless you opt into different ownership behavior
+    - Do **not** assume every stream-based overload behaves identically; some APIs require you to pass stream ownership options explicitly
+- **For caller-provided streams**: When the overload accepts `ReaderOptions`, pass `ReaderOptions.ForExternalStream` or use `ReaderOptions` with `LeaveStreamOpen = true` whenever the caller must retain ownership of the stream
+  - Example: `var options = new ReaderOptions { LeaveStreamOpen = true };`
+  - Or: `var options = ReaderOptions.ForExternalStream;`
+- **For file paths**: SharpCompress manages the stream lifecycle for the internally opened file stream; no manual disposal is needed beyond the archive/reader itself
 - Use `NonDisposingStream` wrapper when working with compression streams directly to prevent disposal
-- Always dispose of readers, writers, and archives in `using` blocks
+- Always dispose of readers, writers, and archives in `using` / `await using` blocks
 - For forward-only operations, use Reader/Writer APIs; for random access, use Archive APIs
 
 ### Async/Await Patterns

src/SharpCompress/Archives/Zip/ZipArchive.Factory.cs

@@ -41,7 +41,7 @@ public static IWritableArchive<ZipWriterOptions> OpenArchive(
             new SourceStream(
                 fileInfo,
                 i => ZipArchiveVolumeFactory.GetFilePart(i, fileInfo),
-                readerOptions ?? new ReaderOptions() { LeaveStreamOpen = false }
+                readerOptions ?? ReaderOptions.ForFilePath
             )
         );
     }
@@ -57,7 +57,7 @@ public static IWritableArchive<ZipWriterOptions> OpenArchive(
             new SourceStream(
                 files[0],
                 i => i < files.Count ? files[i] : null,
-                readerOptions ?? new ReaderOptions() { LeaveStreamOpen = false }
+                readerOptions ?? ReaderOptions.ForFilePath
             )
         );
     }

src/SharpCompress/Readers/ReaderOptions.cs

@@ -24,9 +24,36 @@ namespace SharpCompress.Readers;
 public sealed record ReaderOptions : IReaderOptions
 {
     /// <summary>
-    /// SharpCompress will keep the supplied streams open.  Default is true.
+    /// Whether SharpCompress leaves the supplied streams open when the reader/archive is disposed.
+    /// As of v0.21, the library is documented to close streams by default; this option now defaults to false.
+    /// Set to true when passing caller-owned streams that should not be disposed.
     /// </summary>
-    public bool LeaveStreamOpen { get; init; } = true;
+    /// <remarks>
+    /// <para>
+    /// <b>Default behavior (LeaveStreamOpen = false):</b>
+    /// When you open an archive from a file path (e.g., <c>GZipArchive.OpenArchive(filePath)</c>),
+    /// SharpCompress manages the stream lifetime and closes it on Dispose.
+    /// </para>
+    /// <para>
+    /// <b>Caller-provided streams (LeaveStreamOpen = true):</b>
+    /// When you pass a stream you created (FileStream, MemoryStream, NetworkStream, etc.),
+    /// set LeaveStreamOpen = true to prevent SharpCompress from disposing it.
+    /// Use <see cref="ForExternalStream"/> preset for convenience.
+    /// </para>
+    /// <para>
+    /// <b>Example:</b>
+    /// <code>
+    /// // File-based: stream managed by library
+    /// using var archive = GZipArchive.OpenArchive(filePath); // LeaveStreamOpen = false
+    ///
+    /// // Caller-provided stream: caller manages lifetime
+    /// using var stream = File.OpenRead(filePath);
+    /// var options = new ReaderOptions { LeaveStreamOpen = true };
+    /// using var archive = GZipArchive.OpenArchive(stream, options);
+    /// </code>
+    /// </para>
+    /// </remarks>
+    public bool LeaveStreamOpen { get; init; } = false;
 
     /// <summary>
     /// Encoding to use for archive entry names.