feat: add file drag-and-drop support for images and PDFs

- Add ParsePastedFiles() to detect file paths from paste events
- Support Unix (space-separated with escaping) and Windows (quoted) formats
- Validate file types (PNG, JPG, GIF, WebP, BMP, SVG, PDF)
- Enforce 5MB size limit per file
- Add visual file type indicators with emoji icons
- Integrate with existing attachment system
- Handle edge cases (null chars, trailing backslash, etc.)
- Add comprehensive test coverage

Security hardening:
- Add validateFilePath() to reject path traversal (..) and symlinks
- Use os.Lstat() instead of os.Stat() in all file validation paths
- Return errors from addFileAttachment() and AttachFile()
- Move success notification to InsertFileRefMsg handler where outcome
  is known
- Strip trailing backslash as malformed input
- Add TestValidateFilePath covering symlinks, traversal, regular files

Assisted-By: cagent

Author: ambigois

pkg/tui/components/editor/editor.go

@@ -73,7 +73,7 @@ type Editor interface {
 	// InsertText inserts text at the current cursor position
 	InsertText(text string)
 	// AttachFile adds a file as an attachment and inserts @filepath into the editor
-	AttachFile(filePath string)
+	AttachFile(filePath string) error
 	Cleanup()
 	GetSize() (width, height int)
 	BannerHeight() int
@@ -690,7 +690,9 @@ func (e *editor) Update(msg tea.Msg) (layout.Model, tea.Cmd) {
 		}
 		// Track file references when using @ completion (but not paste placeholders)
 		if e.currentCompletion != nil && e.currentCompletion.Trigger() == "@" && !strings.HasPrefix(msg.Value, "@paste-") {
-			e.addFileAttachment(msg.Value)
+			if err := e.addFileAttachment(msg.Value); err != nil {
+				slog.Warn("failed to add file attachment from completion", "value", msg.Value, "error", err)
+			}
 		}
 		e.clearSuggestion()
 		return e, nil
@@ -1287,14 +1289,17 @@ func (e *editor) InsertText(text string) {
 }
 
 // AttachFile adds a file as an attachment and inserts @filepath into the editor
-func (e *editor) AttachFile(filePath string) {
+func (e *editor) AttachFile(filePath string) error {
 	placeholder := "@" + filePath
-	e.addFileAttachment(placeholder)
+	if err := e.addFileAttachment(placeholder); err != nil {
+		return fmt.Errorf("failed to attach %s: %w", filePath, err)
+	}
 	currentValue := e.textarea.Value()
 	e.textarea.SetValue(currentValue + placeholder + " ")
 	e.textarea.MoveToEnd()
 	e.userTyped = true
 	e.updateAttachmentBanner()
+	return nil
 }
 
 // tryAddFileRef checks if word is a valid @filepath and adds it as attachment.
@@ -1315,33 +1320,36 @@ func (e *editor) tryAddFileRef(word string) {
 		return // not a path-like reference (e.g., @username)
 	}
 
-	e.addFileAttachment(word)
+	if err := e.addFileAttachment(word); err != nil {
+		slog.Debug("speculative file ref not valid", "word", word, "error", err)
+	}
 }
 
 // addFileAttachment adds a file reference as an attachment if valid.
 // The path is resolved to an absolute path so downstream consumers
 // (e.g. processFileAttachment) always receive a fully qualified path.
-func (e *editor) addFileAttachment(placeholder string) {
+func (e *editor) addFileAttachment(placeholder string) error {
 	path := strings.TrimPrefix(placeholder, "@")
 
 	// Resolve to absolute path so the attachment carries a fully qualified
 	// path regardless of the working directory at send time.
 	absPath, err := filepath.Abs(path)
 	if err != nil {
-		slog.Warn("skipping attachment: cannot resolve path", "path", path, "error", err)
-		return
+		return fmt.Errorf("cannot resolve path %s: %w", path, err)
 	}
 
-	// Check if it's an existing file (not directory)
-	info, err := os.Stat(absPath)
-	if err != nil || info.IsDir() {
-		return
+	info, err := validateFilePath(absPath)
+	if err != nil {
+		return fmt.Errorf("invalid file path %s: %w", absPath, err)
+	}
+	if info.IsDir() {
+		return fmt.Errorf("path is a directory: %s", absPath)
 	}
 
 	// Avoid duplicates
 	for _, att := range e.attachments {
 		if att.placeholder == placeholder {
-			return
+			return nil
 		}
 	}
 
@@ -1352,6 +1360,7 @@ func (e *editor) addFileAttachment(placeholder string) {
 		sizeBytes:   int(info.Size()),
 		isTemp:      false,
 	})
+	return nil
 }
 
 // collectAttachments returns structured attachments for all items referenced in
@@ -1451,6 +1460,18 @@ func (e *editor) SendContent() tea.Cmd {
 }
 
 func (e *editor) handlePaste(content string) bool {
+	// First, try to parse as file paths (drag-and-drop)
+	filePaths := ParsePastedFiles(content)
+	if len(filePaths) > 0 && e.allFilesValid(filePaths) {
+		for _, path := range filePaths {
+			if err := e.AttachFile(path); err != nil {
+				slog.Warn("failed to attach dropped file", "path", path, "error", err)
+			}
+		}
+		return true
+	}
+
+	// Not file paths, handle as text paste
 	// Count lines (newlines + 1 for content without trailing newline)
 	lines := strings.Count(content, "\n") + 1
 	if strings.HasSuffix(content, "\n") {
@@ -1477,6 +1498,35 @@ func (e *editor) handlePaste(content string) bool {
 	return true
 }
 
+// allFilesValid checks if all paths exist, are regular files (not dirs/symlinks), and have supported types.
+func (e *editor) allFilesValid(filePaths []string) bool {
+	if len(filePaths) == 0 {
+		return false
+	}
+
+	for _, path := range filePaths {
+		info, err := validateFilePath(path)
+		if err != nil {
+			return false
+		}
+
+		if info.IsDir() {
+			return false
+		}
+
+		if !IsSupportedFileType(path) {
+			return false
+		}
+
+		if info.Size() > 5*1024*1024 {
+			slog.Warn("file too large for attachment", "path", path, "size", info.Size())
+			return false
+		}
+	}
+
+	return true
+}
+
 func (e *editor) updateAttachmentBanner() {
 	if e.banner == nil {
 		return

pkg/tui/components/editor/paste.go

@@ -0,0 +1,227 @@
+package editor
+
+import (
+	"os"
+	"path/filepath"
+	"slices"
+	"strings"
+)
+
+// validateFilePath checks that a path is safe: no path traversal, no symlinks.
+func validateFilePath(path string) (os.FileInfo, error) {
+	clean := filepath.Clean(path)
+	if strings.Contains(clean, "..") {
+		return nil, os.ErrPermission
+	}
+
+	info, err := os.Lstat(clean)
+	if err != nil {
+		return nil, err
+	}
+	if info.Mode()&os.ModeSymlink != 0 {
+		return nil, os.ErrPermission
+	}
+	return info, nil
+}
+
+// Supported file extensions for drag-and-drop attachments
+var supportedFileExtensions = []string{
+	// Images
+	".png", ".jpg", ".jpeg", ".gif", ".webp", ".bmp", ".svg",
+	// PDFs
+	".pdf",
+	// Text files (future)
+	// ".txt", ".md", ".json", ".yaml", ".yml", ".toml",
+}
+
+// ParsePastedFiles attempts to parse pasted content as file paths.
+// It handles different terminal formats:
+// - Unix: space-separated with backslash escaping
+// - Windows Terminal: quote-wrapped paths
+// - Single file: just the path
+//
+// Returns nil if the content doesn't look like file paths.
+func ParsePastedFiles(s string) []string {
+	s = strings.TrimSpace(s)
+	if s == "" {
+		return nil
+	}
+
+	// NOTE: Rio terminal on Windows adds NULL chars for some reason.
+	s = strings.ReplaceAll(s, "\x00", "")
+
+	// Try simple stat first - if all lines are valid files, use them
+	if attemptStatAll(s) {
+		return strings.Split(s, "\n")
+	}
+
+	// Detect Windows Terminal format (quote-wrapped)
+	if os.Getenv("WT_SESSION") != "" {
+		return windowsTerminalParsePastedFiles(s)
+	}
+
+	// Default to Unix format (space-separated with backslash escaping)
+	return unixParsePastedFiles(s)
+}
+
+// attemptStatAll tries to stat each line as a file path.
+// Returns true if ALL lines exist as regular files (not directories or symlinks).
+func attemptStatAll(s string) bool {
+	lines := strings.Split(s, "\n")
+	if len(lines) == 0 {
+		return false
+	}
+
+	for _, line := range lines {
+		line = strings.TrimSpace(line)
+		if line == "" {
+			continue
+		}
+		info, err := validateFilePath(line)
+		if err != nil || info.IsDir() {
+			return false
+		}
+	}
+	return true
+}
+
+// windowsTerminalParsePastedFiles parses Windows Terminal format.
+// Windows Terminal wraps file paths in quotes: "C:\path\to\file.png"
+func windowsTerminalParsePastedFiles(s string) []string {
+	if strings.TrimSpace(s) == "" {
+		return nil
+	}
+
+	var (
+		paths    []string
+		current  strings.Builder
+		inQuotes = false
+	)
+
+	for i := range len(s) {
+		ch := s[i]
+
+		switch {
+		case ch == '"':
+			if inQuotes {
+				// End of quoted section
+				if current.Len() > 0 {
+					paths = append(paths, current.String())
+					current.Reset()
+				}
+				inQuotes = false
+			} else {
+				// Start of quoted section
+				inQuotes = true
+			}
+		case inQuotes:
+			current.WriteByte(ch)
+		case ch != ' ' && ch != '\n' && ch != '\r':
+			// Text outside quotes is not allowed
+			return nil
+		}
+	}
+
+	// Add any remaining content if quotes were properly closed
+	if current.Len() > 0 && !inQuotes {
+		paths = append(paths, current.String())
+	}
+
+	// If quotes were not closed, return nil (malformed input)
+	if inQuotes {
+		return nil
+	}
+
+	return paths
+}
+
+// unixParsePastedFiles parses Unix terminal format.
+// Unix terminals use space-separated paths with backslash escaping.
+// Example: /path/to/file1.png /path/to/my\ file\ with\ spaces.jpg
+func unixParsePastedFiles(s string) []string {
+	if strings.TrimSpace(s) == "" {
+		return nil
+	}
+
+	var (
+		paths   []string
+		current strings.Builder
+		escaped = false
+	)
+
+	for i := range len(s) {
+		ch := s[i]
+
+		switch {
+		case escaped:
+			// After a backslash, add the character as-is (including space)
+			current.WriteByte(ch)
+			escaped = false
+		case ch == '\\':
+			if i == len(s)-1 {
+				// Trailing backslash is malformed input; strip it
+				break
+			}
+			escaped = true
+		case ch == ' ' || ch == '\n' || ch == '\r':
+			// Space/newline separates paths (unless escaped)
+			if current.Len() > 0 {
+				paths = append(paths, current.String())
+				current.Reset()
+			}
+		default:
+			current.WriteByte(ch)
+		}
+	}
+
+	// Handle trailing backslash if present
+	if escaped {
+		current.WriteByte('\\')
+	}
+
+	// Add the last path if any
+	if current.Len() > 0 {
+		paths = append(paths, current.String())
+	}
+
+	return paths
+}
+
+// IsSupportedFileType checks if a file has a supported extension.
+func IsSupportedFileType(path string) bool {
+	ext := strings.ToLower(filepath.Ext(path))
+	return slices.Contains(supportedFileExtensions, ext)
+}
+
+// GetFileType returns a human-readable file type for display.
+func GetFileType(path string) string {
+	ext := strings.ToLower(filepath.Ext(path))
+	switch ext {
+	case ".png", ".jpg", ".jpeg", ".gif", ".webp", ".bmp", ".svg":
+		return "image"
+	case ".pdf":
+		return "pdf"
+	case ".txt", ".md":
+		return "text"
+	case ".json", ".yaml", ".yml", ".toml":
+		return "config"
+	default:
+		return "file"
+	}
+}
+
+// GetFileIcon returns an emoji icon for a file type.
+func GetFileIcon(fileType string) string {
+	switch fileType {
+	case "image":
+		return "🖼️"
+	case "pdf":
+		return "📄"
+	case "text":
+		return "📝"
+	case "config":
+		return "⚙️"
+	default:
+		return "📎"
+	}
+}