feat: add clipboard image handling for pasting and staging attachments

src/EchoHub.Client/AppOrchestrator.cs

@@ -35,6 +35,10 @@ public sealed class AppOrchestrator : IDisposable
     private readonly HashSet<string> _channelsLoadingMore = new(StringComparer.OrdinalIgnoreCase);
     private readonly List<string> _stagedAttachments = [];
 
+    // Temp PNGs created for clipboard-image pastes; deleted once their message is sent
+    // (or the staging tray is cleared) so pasted screenshots don't pile up in %TEMP%.
+    private readonly HashSet<string> _tempPastedFiles = [];
+
     // E2E channels whose unlock prompt the user cancelled — don't nag on every reselect.
     // Cleared on connect/reconnect; an explicit /join or a send attempt re-offers the prompt.
     private readonly HashSet<string> _declinedUnlocks = new(StringComparer.OrdinalIgnoreCase);
@@ -94,6 +98,8 @@ public sealed class AppOrchestrator : IDisposable
         _mainWindow.OnDisconnectRequested += HandleDisconnect;
         _mainWindow.OnLogoutRequested += HandleLogout;
         _mainWindow.OnMessageSubmitted += HandleMessageSubmitted;
+        _mainWindow.OnFilesStaged += HandleFilesStaged;
+        _mainWindow.OnImagePasted += HandleImagePasted;
         _mainWindow.OnChannelSelected += HandleChannelSelected;
         _mainWindow.OnProfileRequested += HandleProfileRequested;
         _mainWindow.OnStatusRequested += HandleStatusRequested;
@@ -221,11 +227,89 @@ public sealed class AppOrchestrator : IDisposable
 
     private Task HandleCmdClearAttachments()
     {
+        var temps = _stagedAttachments.Where(_tempPastedFiles.Contains).ToList();
+        _tempPastedFiles.ExceptWith(temps);
+        CleanupPastedTempFiles(temps);
+
         _stagedAttachments.Clear();
         InvokeUI(RefreshStagingTray);
         return Task.CompletedTask;
     }
 
+    /// <summary>
+    /// Stages a batch of local files (multi-file paste or drag-and-drop) as attachments of the
+    /// next message. Runs synchronously on the UI thread — unlike routing each file through a
+    /// fire-and-forget /send command, a 10-file paste can't race the staging list.
+    /// </summary>
+    private void HandleFilesStaged(string channel, IReadOnlyList<string> files)
+    {
+        if (!_conn.IsAuthenticated || !_conn.IsConnected)
+            return;
+
+        var slotsLeft = HubConstants.MaxAttachmentsPerMessage - _stagedAttachments.Count;
+        _stagedAttachments.AddRange(files.Take(Math.Max(0, slotsLeft)));
+
+        if (files.Count > slotsLeft)
+            _mainWindow.ShowError($"You can attach at most {HubConstants.MaxAttachmentsPerMessage} files per message.");
+
+        RefreshStagingTray();
+    }
+
+    /// <summary>
+    /// Stages an image pasted as raw clipboard data (copied from a browser, a screenshot tool,
+    /// or an image editor). The PNG is written to a per-paste temp folder so it flows through
+    /// the same path-based staging/encryption pipeline as regular files, and the temp file is
+    /// deleted once the message is sent.
+    /// </summary>
+    private void HandleImagePasted(string channel, byte[] png)
+    {
+        if (!_conn.IsAuthenticated || !_conn.IsConnected)
+            return;
+
+        if (_stagedAttachments.Count >= HubConstants.MaxAttachmentsPerMessage)
+        {
+            _mainWindow.ShowError($"You can attach at most {HubConstants.MaxAttachmentsPerMessage} files per message.");
+            return;
+        }
+
+        try
+        {
+            // A unique folder per paste keeps the Discord-style "image.png" display name
+            // while letting several pasted images coexist in one message.
+            var dir = Path.Combine(Path.GetTempPath(), "EchoHub", "pasted", Guid.NewGuid().ToString("N")[..8]);
+            Directory.CreateDirectory(dir);
+            var path = Path.Combine(dir, "image.png");
+            File.WriteAllBytes(path, png);
+
+            _tempPastedFiles.Add(path);
+            _stagedAttachments.Add(path);
+            RefreshStagingTray();
+        }
+        catch (Exception ex)
+        {
+            Log.Error(ex, "Staging a pasted clipboard image failed");
+            _mainWindow.ShowError($"Pasting image failed: {ex.Message}");
+        }
+    }
+
+    /// <summary>Best-effort removal of pasted-image temp files and their per-paste folders.</summary>
+    private static void CleanupPastedTempFiles(IReadOnlyList<string> files)
+    {
+        foreach (var file in files)
+        {
+            try
+            {
+                File.Delete(file);
+                if (Path.GetDirectoryName(file) is { } dir)
+                    Directory.Delete(dir);
+            }
+            catch (Exception ex)
+            {
+                Log.Debug(ex, "Could not delete pasted-image temp file {File}", file);
+            }
+        }
+    }
+
     /// <summary>
     /// Opens the ASCII-art size picker (no argument) or sets it directly from "s"/"m"/"l" (or
     /// small/medium/large). The choice is a persistent preference applied to attached images.
@@ -307,17 +391,29 @@ public sealed class AppOrchestrator : IDisposable
             _stagedAttachments.Clear();
             InvokeUI(RefreshStagingTray);
 
-            var hasRoomKey = _conn.RoomKeys.TryGetKey(channel, out var roomKey);
+            // Pasted clipboard images live in temp files; once this send owns them they are
+            // deleted whether the upload succeeds or fails (the tray is already cleared).
+            var tempFiles = staged.Where(_tempPastedFiles.Contains).ToList();
+            _tempPastedFiles.ExceptWith(tempFiles);
 
-            var outgoing = new List<OutgoingAttachment>();
-            foreach (var path in staged)
-                outgoing.Add(await BuildOutgoingAttachmentAsync(path, hasRoomKey ? roomKey : null, size));
+            try
+            {
+                var hasRoomKey = _conn.RoomKeys.TryGetKey(channel, out var roomKey);
 
-            var wireContent = hasRoomKey && !string.IsNullOrEmpty(content)
-                ? RoomCrypto.EncryptText(content, roomKey)
-                : content;
+                var outgoing = new List<OutgoingAttachment>();
+                foreach (var path in staged)
+                    outgoing.Add(await BuildOutgoingAttachmentAsync(path, hasRoomKey ? roomKey : null, size));
 
-            await _conn.Api!.SendMessageWithAttachmentsAsync(channel, wireContent, outgoing, size);
+                var wireContent = hasRoomKey && !string.IsNullOrEmpty(content)
+                    ? RoomCrypto.EncryptText(content, roomKey)
+                    : content;
+
+                await _conn.Api!.SendMessageWithAttachmentsAsync(channel, wireContent, outgoing, size);
+            }
+            finally
+            {
+                CleanupPastedTempFiles(tempFiles);
+            }
         }, "Send failed");
     }
 

src/EchoHub.Client/Services/ClipboardImage.cs

@@ -0,0 +1,257 @@
+using System.Diagnostics;
+using System.Runtime.InteropServices;
+using System.Runtime.Versioning;
+using Serilog;
+using SixLabors.ImageSharp;
+
+namespace EchoHub.Client.Services;
+
+/// <summary>
+/// Reads raw image data from the OS clipboard (e.g. an image copied from a browser, or a
+/// Win+Shift+S screenshot), which terminals cannot paste as text. Always returns PNG bytes:
+/// clipboard PNG data is passed through, clipboard bitmaps (CF_DIB) are re-encoded.
+/// </summary>
+public static class ClipboardImage
+{
+    private static readonly byte[] PngMagic = [0x89, 0x50, 0x4E, 0x47];
+
+    public static bool TryGetPng(out byte[] png)
+    {
+        png = [];
+        try
+        {
+            if (OperatingSystem.IsWindows())
+                return TryGetWindows(out png);
+            if (OperatingSystem.IsLinux())
+                return TryGetLinux(out png);
+            if (OperatingSystem.IsMacOS())
+                return TryGetMacOS(out png);
+        }
+        catch (Exception ex)
+        {
+            Log.Warning(ex, "Reading an image from the clipboard failed");
+        }
+
+        return false;
+    }
+
+    private static bool IsPng(byte[] data) =>
+        data.Length > PngMagic.Length && data.AsSpan(0, PngMagic.Length).SequenceEqual(PngMagic);
+
+    /// <summary>
+    /// Converts clipboard DIB bytes (a BITMAPINFOHEADER/V4/V5 + optional palette/masks + pixel
+    /// data, i.e. a .bmp file without its 14-byte file header) to PNG. Returns null when the
+    /// data is malformed or not decodable as a bitmap.
+    /// </summary>
+    public static byte[]? DibToPng(byte[] dib)
+    {
+        if (dib.Length < 40)
+            return null;
+
+        var headerSize = BitConverter.ToInt32(dib, 0);
+        if (headerSize < 40 || headerSize > dib.Length)
+            return null;
+
+        var bitCount = BitConverter.ToUInt16(dib, 14);
+        var compression = BitConverter.ToUInt32(dib, 16);
+        var clrUsed = BitConverter.ToUInt32(dib, 32);
+
+        // Pixel data offset: file header + info header + color masks + palette.
+        // BI_BITFIELDS masks follow a plain 40-byte header; larger headers embed them.
+        var maskBytes = headerSize == 40 && compression == 3 ? 12
+                      : headerSize == 40 && compression == 6 ? 16
+                      : 0;
+        var paletteEntries = clrUsed != 0 ? clrUsed
+                           : bitCount <= 8 ? 1u << bitCount
+                           : 0u;
+        var pixelOffset = (uint)(14 + headerSize + maskBytes) + paletteEntries * 4;
+
+        var bmp = new byte[14 + dib.Length];
+        bmp[0] = (byte)'B';
+        bmp[1] = (byte)'M';
+        BitConverter.TryWriteBytes(bmp.AsSpan(2), (uint)bmp.Length);
+        BitConverter.TryWriteBytes(bmp.AsSpan(10), pixelOffset);
+        dib.CopyTo(bmp, 14);
+
+        try
+        {
+            using var image = Image.Load(bmp);
+            using var ms = new MemoryStream();
+            image.SaveAsPng(ms);
+            return ms.ToArray();
+        }
+        catch (Exception ex) when (ex is ImageFormatException or InvalidOperationException)
+        {
+            Log.Warning(ex, "Clipboard DIB could not be decoded as a bitmap");
+            return null;
+        }
+    }
+
+    // ── Windows: "PNG" / "image/png" registered formats, then CF_DIB ─────────
+
+    private const uint CfDib = 8;
+
+    [SupportedOSPlatform("windows")]
+    private static bool TryGetWindows(out byte[] png)
+    {
+        png = [];
+
+        // Browsers register a "PNG" (Chromium) or "image/png" (some apps) clipboard format
+        // preserving transparency; CF_DIB is synthesized by Windows for everything else
+        // (screenshots, image editors), so together these cover all image sources.
+        var pngFormat = RegisterClipboardFormatW("PNG");
+        var mimeFormat = RegisterClipboardFormatW("image/png");
+
+        var hasAny = (pngFormat != 0 && IsClipboardFormatAvailable(pngFormat))
+                  || (mimeFormat != 0 && IsClipboardFormatAvailable(mimeFormat))
+                  || IsClipboardFormatAvailable(CfDib);
+        if (!hasAny)
+            return false;
+
+        var opened = false;
+        for (var attempt = 0; attempt < 5 && !opened; attempt++)
+            opened = OpenClipboard(IntPtr.Zero);
+        if (!opened)
+            return false;
+
+        try
+        {
+            foreach (var format in new[] { pngFormat, mimeFormat })
+            {
+                if (format == 0 || !IsClipboardFormatAvailable(format))
+                    continue;
+                var data = ReadHGlobal(GetClipboardData(format));
+                if (data is not null && IsPng(data))
+                {
+                    png = data;
+                    return true;
+                }
+            }
+
+            if (IsClipboardFormatAvailable(CfDib)
+                && ReadHGlobal(GetClipboardData(CfDib)) is { } dib
+                && DibToPng(dib) is { } converted)
+            {
+                png = converted;
+                return true;
+            }
+
+            return false;
+        }
+        finally
+        {
+            CloseClipboard();
+        }
+    }
+
+    [SupportedOSPlatform("windows")]
+    private static byte[]? ReadHGlobal(IntPtr handle)
+    {
+        if (handle == IntPtr.Zero)
+            return null;
+
+        var ptr = GlobalLock(handle);
+        if (ptr == IntPtr.Zero)
+            return null;
+
+        try
+        {
+            var size = (int)GlobalSize(handle);
+            if (size <= 0)
+                return null;
+            var data = new byte[size];
+            Marshal.Copy(ptr, data, 0, size);
+            return data;
+        }
+        finally
+        {
+            GlobalUnlock(handle);
+        }
+    }
+
+    [DllImport("user32.dll", SetLastError = true)]
+    [return: MarshalAs(UnmanagedType.Bool)]
+    private static extern bool OpenClipboard(IntPtr hWndNewOwner);
+
+    [DllImport("user32.dll", SetLastError = true)]
+    [return: MarshalAs(UnmanagedType.Bool)]
+    private static extern bool CloseClipboard();
+
+    [DllImport("user32.dll", SetLastError = true)]
+    [return: MarshalAs(UnmanagedType.Bool)]
+    private static extern bool IsClipboardFormatAvailable(uint format);
+
+    [DllImport("user32.dll", SetLastError = true)]
+    private static extern IntPtr GetClipboardData(uint uFormat);
+
+    [DllImport("user32.dll", CharSet = CharSet.Unicode, SetLastError = true)]
+    private static extern uint RegisterClipboardFormatW(string lpszFormat);
+
+    [DllImport("kernel32.dll", SetLastError = true)]
+    private static extern IntPtr GlobalLock(IntPtr hMem);
+
+    [DllImport("kernel32.dll", SetLastError = true)]
+    [return: MarshalAs(UnmanagedType.Bool)]
+    private static extern bool GlobalUnlock(IntPtr hMem);
+
+    [DllImport("kernel32.dll", SetLastError = true)]
+    private static extern nuint GlobalSize(IntPtr hMem);
+
+    // ── Linux: image/png via wl-paste or xclip ────────────────────────────────
+
+    [SupportedOSPlatform("linux")]
+    private static bool TryGetLinux(out byte[] png)
+    {
+        png = [];
+        var data = RunForBytes("wl-paste", ["--type", "image/png"])
+                ?? RunForBytes("xclip", ["-selection", "clipboard", "-t", "image/png", "-o"]);
+        if (data is null || !IsPng(data))
+            return false;
+
+        png = data;
+        return true;
+    }
+
+    // ── macOS: pngpaste (brew install pngpaste), when present ────────────────
+
+    [SupportedOSPlatform("macos")]
+    private static bool TryGetMacOS(out byte[] png)
+    {
+        png = [];
+        var data = RunForBytes("pngpaste", ["-"]);
+        if (data is null || !IsPng(data))
+            return false;
+
+        png = data;
+        return true;
+    }
+
+    private static byte[]? RunForBytes(string fileName, IEnumerable<string> args)
+    {
+        var psi = new ProcessStartInfo(fileName)
+        {
+            RedirectStandardOutput = true,
+            RedirectStandardError = true,
+            UseShellExecute = false,
+            CreateNoWindow = true,
+        };
+        foreach (var arg in args)
+            psi.ArgumentList.Add(arg);
+
+        try
+        {
+            using var process = Process.Start(psi);
+            if (process is null)
+                return null;
+
+            using var ms = new MemoryStream();
+            process.StandardOutput.BaseStream.CopyTo(ms);
+            process.WaitForExit(2000);
+            return process.ExitCode == 0 && ms.Length > 0 ? ms.ToArray() : null;
+        }
+        catch (Exception ex) when (ex is System.ComponentModel.Win32Exception or FileNotFoundException)
+        {
+            return null; // tool not installed
+        }
+    }
+}

src/EchoHub.Client/UI/MainWindow.cs

@@ -87,6 +87,18 @@ public sealed partial class MainWindow : Runnable
     /// </summary>
     public event Action<string, string>? OnMessageSubmitted;
 
+    /// <summary>
+    /// Fired when local files arrive via paste or drag-and-drop to be staged as attachments.
+    /// Parameters: channel name, absolute paths of existing files.
+    /// </summary>
+    public event Action<string, IReadOnlyList<string>>? OnFilesStaged;
+
+    /// <summary>
+    /// Fired when raw image data is pasted from the clipboard (e.g. copied from a browser or a
+    /// screenshot tool). Parameters: channel name, PNG-encoded image bytes.
+    /// </summary>
+    public event Action<string, byte[]>? OnImagePasted;
+
     /// <summary>
     /// Fired when the user requests to connect via the menu.
     /// </summary>
@@ -744,11 +756,15 @@ public sealed partial class MainWindow : Runnable
         }
         else if (e.KeyCode == CtrlVKey.KeyCode || e.KeyCode == CtrlYKey.KeyCode)
         {
-            // If a file was copied in the OS file manager, the clipboard holds a file list
-            // (not text) — attach it. Otherwise paste text. This is the reliable path on
-            // Windows Terminal, which never pastes copied files as text.
+            // Discord-style paste priority. Copied files in the OS file manager put a file
+            // list (not text) on the clipboard — attach them all. Copied image data (browser
+            // right-click copy, screenshot tools) is attached as a PNG. Otherwise paste text.
+            // Terminals never deliver either of the first two as text, so this is the only path.
             if (ClipboardFiles.TryGetFiles(out var pastedFiles))
                 StageFiles(pastedFiles);
+            else if (!string.IsNullOrEmpty(_messageManager.CurrentChannel)
+                     && ClipboardImage.TryGetPng(out var pastedPng))
+                OnImagePasted?.Invoke(_messageManager.CurrentChannel, pastedPng);
             else
                 GuardedClipboardAction(() => _inputField.Paste(), "paste");
             e.Handled = true;
@@ -872,17 +888,16 @@ public sealed partial class MainWindow : Runnable
     }
 
     /// <summary>
-    /// Routes files (from a drop or a file-clipboard paste) through the /send pipeline, which
-    /// stages them; the next Enter sends them with any typed caption.
+    /// Stages files (from a drop or a file-clipboard paste) as attachments in one batch; the
+    /// next Enter sends them with any typed caption.
     /// </summary>
-    private void StageFiles(IEnumerable<string> files)
+    private void StageFiles(IReadOnlyList<string> files)
     {
         var channel = _messageManager.CurrentChannel;
         if (string.IsNullOrEmpty(channel))
             return;
 
-        foreach (var file in files)
-            OnMessageSubmitted?.Invoke(channel, $"/send \"{file}\"");
+        OnFilesStaged?.Invoke(channel, files);
     }
 
     private void OnChatViewportChanged()