feat(ui): attach large text pastes as virtual files

Offer to turn sufficiently large plain-text clipboard pastes into
pasted-context-N.txt attachments instead of inserting them into the
composer, with ask/attach/inline composer settings.

Co-authored-by: Serhii Dziupin <makeittech@users.noreply.github.com>

packages/ui/src/components/chat/ChatInput.tsx

@@ -82,7 +82,13 @@ import { eventMatchesShortcut, getEffectiveShortcutCombo, normalizeCombo } from
 import {
     assignImageAttachmentFilenames,
     buildAttachmentCitationText,
+    nextPastedContextFilename,
 } from './attachmentCitations';
+import {
+    createPastedContextFile,
+    isLargePlainTextPaste,
+} from './composer/largeTextPaste';
+import type { LargeTextPasteBehavior } from '@/stores/useUIStore';
 import type { FileMentionAutocompleteInputSource } from './fileMentionAutocompleteState';
 import {
     classifyMention,
@@ -288,6 +294,8 @@ const ChatInputComponent: React.FC<ChatInputProps> = ({ onOpenSettings, scrollTo
     const messageRef = React.useRef(message);
     const currentChatDraftIdentityRef = React.useRef<ChatDraftIdentity | null>(initialDraftIdentityRef.current);
     const pendingPastedAttachmentFilenamesRef = React.useRef<Set<string>>(new Set());
+    const largeTextPasteToastIdRef = React.useRef<string | number | null>(null);
+    const largeTextPasteOfferIdRef = React.useRef(0);
 
     // TODO: port sendMessage to session-actions (complex — creates sessions, handles attachments, etc.)
     // eslint-disable-next-line @typescript-eslint/no-explicit-any
@@ -358,6 +366,7 @@ const ChatInputComponent: React.FC<ChatInputProps> = ({ onOpenSettings, scrollTo
     const inputBarOffset = useUIStore((state) => state.inputBarOffset);
     const persistChatDraft = useUIStore((state) => state.persistChatDraft);
     const inputSpellcheckEnabled = useUIStore((state) => state.inputSpellcheckEnabled);
+    const largeTextPasteBehavior = useUIStore((state) => state.largeTextPasteBehavior);
     const isExpandedInput = useUIStore((state) => state.isExpandedInput);
     const setExpandedInput = useUIStore((state) => state.setExpandedInput);
     const setTimelineDialogOpen = useUIStore((state) => state.setTimelineDialogOpen);
@@ -1723,14 +1732,124 @@ const ChatInputComponent: React.FC<ChatInputProps> = ({ onOpenSettings, scrollTo
 
         const imageFiles = Array.from(fileMap.values());
         const pastedText = e.clipboardData.getData('text');
+        const sessionReady = Boolean(currentSessionId || newSessionDraftOpen);
+
         if (imageFiles.length === 0) {
-            if (pastedText.includes('@')) {
-                markFileMentionPasteSuppression();
+            const behavior: LargeTextPasteBehavior = largeTextPasteBehavior;
+            const shouldOfferLargePaste = sessionReady
+                && inputMode === 'normal'
+                && behavior !== 'inline'
+                && isLargePlainTextPaste(pastedText);
+
+            if (!shouldOfferLargePaste) {
+                if (pastedText.includes('@')) {
+                    markFileMentionPasteSuppression();
+                }
+                return;
             }
+
+            // Must run synchronously — ComposerEditor does not consume paste.
+            e.preventDefault();
+
+            const pasteInline = () => {
+                if (pastedText.includes('@')) {
+                    markFileMentionPasteSuppression();
+                }
+                insertTextAtSelection(
+                    pastedText,
+                    getFileMentionInputSourceForInsertedText(pastedText),
+                );
+            };
+
+            const attachAsFile = async () => {
+                const filename = nextPastedContextFilename([
+                    ...attachedFiles.map((file) => file.filename),
+                    ...pendingPastedAttachmentFilenamesRef.current,
+                ]);
+                const citationText = buildAttachmentCitationText([filename]);
+                const textarea = composerRef.current;
+                const selectionStart = textarea?.getSelection().start ?? message.length;
+                const selectionEnd = textarea?.getSelection().end ?? message.length;
+                const insertionText = withInlineInsertionBoundaries(
+                    citationText,
+                    message.slice(0, selectionStart),
+                    message.slice(selectionEnd),
+                );
+
+                insertTextAtSelection(
+                    insertionText,
+                    getFileMentionInputSourceForInsertedText(insertionText),
+                );
+
+                const file = createPastedContextFile(pastedText, filename);
+                pendingPastedAttachmentFilenamesRef.current.add(filename);
+                try {
+                    await addAttachedFile(file);
+                } catch (error) {
+                    console.error('Clipboard text attach failed', error);
+                    toast.error(
+                        error instanceof Error
+                            ? error.message
+                            : t('chat.chatInput.toast.clipboardTextAttachFailed'),
+                    );
+                } finally {
+                    pendingPastedAttachmentFilenamesRef.current.delete(filename);
+                }
+            };
+
+            if (behavior === 'attach') {
+                await attachAsFile();
+                return;
+            }
+
+            const offerId = largeTextPasteOfferIdRef.current + 1;
+            largeTextPasteOfferIdRef.current = offerId;
+
+            if (largeTextPasteToastIdRef.current !== null) {
+                // Invalidate first so a synchronous onDismiss from dismiss()
+                // cannot apply the superseded paste.
+                toast.dismiss(largeTextPasteToastIdRef.current);
+                largeTextPasteToastIdRef.current = null;
+            }
+
+            const resolveLargePaste = (action: 'attach' | 'inline') => {
+                if (offerId !== largeTextPasteOfferIdRef.current) {
+                    return;
+                }
+                // Invalidate this offer so a later onDismiss cannot double-apply.
+                largeTextPasteOfferIdRef.current += 1;
+                largeTextPasteToastIdRef.current = null;
+                if (action === 'attach') {
+                    void attachAsFile();
+                    return;
+                }
+                pasteInline();
+            };
+
+            largeTextPasteToastIdRef.current = toast.info(
+                t('chat.chatInput.toast.largeTextPaste.title'),
+                {
+                    description: t('chat.chatInput.toast.largeTextPaste.description'),
+                    duration: Infinity,
+                    action: {
+                        label: t('chat.chatInput.toast.largeTextPaste.attach'),
+                        onClick: () => resolveLargePaste('attach'),
+                    },
+                    cancel: {
+                        label: t('chat.chatInput.toast.largeTextPaste.inline'),
+                        onClick: () => resolveLargePaste('inline'),
+                    },
+                    onDismiss: () => {
+                        // Dismissing without a choice keeps the paste — insert inline
+                        // so clipboard content is not lost.
+                        resolveLargePaste('inline');
+                    },
+                },
+            );
             return;
         }
 
-        if (!currentSessionId && !newSessionDraftOpen) {
+        if (!sessionReady) {
             if (pastedText.includes('@')) {
                 markFileMentionPasteSuppression();
             }
@@ -1771,7 +1890,7 @@ const ChatInputComponent: React.FC<ChatInputProps> = ({ onOpenSettings, scrollTo
                 pendingPastedAttachmentFilenamesRef.current.delete(filename);
             }
         }
-    }, [addAttachedFile, attachedFiles, currentSessionId, inputMode, markFileMentionPasteSuppression, message, newSessionDraftOpen, insertTextAtSelection, setMessage, t, updateAutocompleteState]);
+    }, [addAttachedFile, attachedFiles, currentSessionId, inputMode, largeTextPasteBehavior, markFileMentionPasteSuppression, message, newSessionDraftOpen, insertTextAtSelection, setMessage, t, updateAutocompleteState]);
 
     const handleFileSelect = (file: { name: string; path: string; relativePath?: string }) => {
 

packages/ui/src/components/chat/__tests__/attachmentCitations.test.ts

@@ -5,6 +5,7 @@ import {
     buildAttachmentCitationText,
     findAttachmentCitationRanges,
     isGenericImageFilename,
+    nextPastedContextFilename,
 } from '../attachmentCitations';
 
 describe('attachment citations', () => {
@@ -53,4 +54,10 @@ describe('attachment citations', () => {
             ['desktop.jpg'],
         )).toEqual([{ start: 8, end: 21 }]);
     });
+
+    test('assigns sequential pasted-context filenames', () => {
+        expect(nextPastedContextFilename([])).toBe('pasted-context-1.txt');
+        expect(nextPastedContextFilename(['pasted-context-1.txt', 'notes.md'])).toBe('pasted-context-2.txt');
+        expect(nextPastedContextFilename(['PASTED-CONTEXT-2.TXT'])).toBe('pasted-context-1.txt');
+    });
 });

packages/ui/src/components/chat/attachmentCitations.ts

@@ -144,6 +144,20 @@ export const assignImageAttachmentFilenames = (
     });
 };
 
+/** Next unused `pasted-context-N.txt` name for a large text paste attachment. */
+export const nextPastedContextFilename = (existingFilenames: string[]): string => {
+    const used = new Set(existingFilenames.map(normalizeFilenameKey));
+
+    for (let index = 1; index < Number.MAX_SAFE_INTEGER; index += 1) {
+        const candidate = `pasted-context-${index}.txt`;
+        if (!used.has(normalizeFilenameKey(candidate))) {
+            return candidate;
+        }
+    }
+
+    return `pasted-context-${Date.now()}.txt`;
+};
+
 export const buildAttachmentCitationText = (filenames: string[]): string => (
     filenames.map((filename) => `[${filename}]`).join(' ')
 );

packages/ui/src/components/chat/composer/DOCUMENTATION.md

@@ -18,6 +18,16 @@ belongs to one of them.
 | `attachments/` | Files: paths, drop payloads |
 | `ui/` | Presentation |
 | `text.ts` | How inserted text meets the text already there |
+| `largeTextPaste.ts` | Detect large plain-text pastes and build virtual `.txt` files |
+
+`ChatInput.handlePaste` owns paste orchestration: URL-over-selection markdown
+links, clipboard images (attach + citation), and large plain-text pastes.
+Large pastes (about 2,000 characters or 25 lines) follow the composer setting
+`largeTextPasteBehavior` (`ask` / `attach` / `inline`). Attaching creates an
+in-memory `text/plain` file named `pasted-context-N.txt`, inserts a bracket
+citation, and sends it through the same attachment pipeline as a manually
+picked `.txt` file. Short text, images, and URL wraps keep their existing
+paths.
 
 ## The prompt language
 
@@ -119,8 +129,8 @@ hardware.
 
 The package has no DOM test environment, so coverage stops at the state and
 logic layers: the language, the submit assembly, path and drop handling, text
-splicing, message history, and the CodeMirror language extension at the
-`EditorState` level.
+splicing, large-paste detection, message history, and the CodeMirror language
+extension at the `EditorState` level.
 
 Rendering, focus, keyboard behavior, IME and WKWebView are **not covered by
 tests** and are verified by hand. Do not report a change to them as validated

packages/ui/src/components/chat/composer/__tests__/largeTextPaste.test.ts

@@ -0,0 +1,45 @@
+import { describe, expect, test } from 'bun:test';
+
+import {
+    LARGE_TEXT_PASTE_CHAR_THRESHOLD,
+    LARGE_TEXT_PASTE_LINE_THRESHOLD,
+    createPastedContextFile,
+    isLargePlainTextPaste,
+} from '../largeTextPaste';
+
+describe('large text paste helpers', () => {
+    test('treats short text as not large', () => {
+        expect(isLargePlainTextPaste('hello world')).toBe(false);
+        expect(isLargePlainTextPaste('line1\nline2\nline3')).toBe(false);
+    });
+
+    test('treats empty and whitespace-only pastes as not large', () => {
+        expect(isLargePlainTextPaste('')).toBe(false);
+        expect(isLargePlainTextPaste('   \n\t  ')).toBe(false);
+    });
+
+    test('detects pastes at the character threshold', () => {
+        const text = 'a'.repeat(LARGE_TEXT_PASTE_CHAR_THRESHOLD);
+        expect(isLargePlainTextPaste(text)).toBe(true);
+        expect(isLargePlainTextPaste(text.slice(0, -1))).toBe(false);
+    });
+
+    test('detects pastes at the line threshold', () => {
+        const lines = Array.from({ length: LARGE_TEXT_PASTE_LINE_THRESHOLD }, (_, index) => `line ${index}`);
+        expect(isLargePlainTextPaste(lines.join('\n'))).toBe(true);
+        expect(isLargePlainTextPaste(lines.slice(0, -1).join('\n'))).toBe(false);
+    });
+
+    test('honors custom thresholds', () => {
+        expect(isLargePlainTextPaste('abcdef', { charThreshold: 5 })).toBe(true);
+        expect(isLargePlainTextPaste('a\nb\nc', { lineThreshold: 3 })).toBe(true);
+        expect(isLargePlainTextPaste('a\nb', { lineThreshold: 3, charThreshold: 100 })).toBe(false);
+    });
+
+    test('creates a text/plain file with the given name', async () => {
+        const file = createPastedContextFile('architecture notes', 'pasted-context-1.txt');
+        expect(file.name).toBe('pasted-context-1.txt');
+        expect(file.type.startsWith('text/plain')).toBe(true);
+        expect(await file.text()).toBe('architecture notes');
+    });
+});

packages/ui/src/components/chat/composer/largeTextPaste.ts

@@ -0,0 +1,55 @@
+/**
+ * Large plain-text paste → virtual file attachment helpers.
+ *
+ * Detect when clipboard text is large enough that inserting it into the
+ * composer would clutter the prompt, and build an in-memory text/plain File
+ * the attachment pipeline can send like any other .txt attachment.
+ */
+
+export const LARGE_TEXT_PASTE_CHAR_THRESHOLD = 2000;
+export const LARGE_TEXT_PASTE_LINE_THRESHOLD = 25;
+
+const countLines = (text: string): number => {
+  let lines = 1;
+  for (let index = 0; index < text.length; index += 1) {
+    if (text.charCodeAt(index) === 10) {
+      lines += 1;
+    }
+  }
+  return lines;
+};
+
+/**
+ * Whether pasted plain text should be offered (or auto-handled) as a file
+ * attachment instead of being inserted into the composer.
+ *
+ * Empty / whitespace-only pastes are never large. Thresholds are OR'd:
+ * character count or line count is enough.
+ */
+export const isLargePlainTextPaste = (
+  text: string,
+  options?: {
+    charThreshold?: number;
+    lineThreshold?: number;
+  },
+): boolean => {
+  if (!text || !text.trim()) {
+    return false;
+  }
+
+  const charThreshold = options?.charThreshold ?? LARGE_TEXT_PASTE_CHAR_THRESHOLD;
+  const lineThreshold = options?.lineThreshold ?? LARGE_TEXT_PASTE_LINE_THRESHOLD;
+
+  if (text.length >= charThreshold) {
+    return true;
+  }
+
+  return countLines(text) >= lineThreshold;
+};
+
+export const createPastedContextFile = (text: string, filename: string): File => (
+  new File([text], filename, {
+    type: 'text/plain',
+    lastModified: Date.now(),
+  })
+);

packages/ui/src/components/sections/openchamber/OpenChamberPage.tsx

@@ -206,6 +206,7 @@ const ChatSectionContent: React.FC = () => {
                 'followUpBehavior',
                 'persistDraft',
                 'inputSpellcheck',
+                'largeTextPaste',
             ]}
         />
     );

packages/ui/src/components/sections/openchamber/OpenChamberVisualSettings.tsx

@@ -3,7 +3,7 @@ import { runtimeFetch } from '@/lib/runtime-fetch';
 
 import { useThemeSystem } from '@/contexts/useThemeSystem';
 import type { ThemeMode } from '@/types/theme';
-import { useUIStore } from '@/stores/useUIStore';
+import { useUIStore, type LargeTextPasteBehavior } from '@/stores/useUIStore';
 import { useMessageQueueStore, type FollowUpBehavior } from '@/stores/messageQueueStore';
 import { cn } from '@/lib/utils';
 import { Button } from '@/components/ui/button';
@@ -275,11 +275,26 @@ const FOLLOW_UP_BEHAVIOR_OPTIONS: Option<FollowUpBehavior>[] = [
     },
 ];
 
+const LARGE_TEXT_PASTE_BEHAVIOR_OPTIONS: Option<LargeTextPasteBehavior>[] = [
+    {
+        id: 'ask',
+        labelKey: 'settings.openchamber.visual.option.largeTextPaste.ask.label',
+    },
+    {
+        id: 'attach',
+        labelKey: 'settings.openchamber.visual.option.largeTextPaste.attach.label',
+    },
+    {
+        id: 'inline',
+        labelKey: 'settings.openchamber.visual.option.largeTextPaste.inline.label',
+    },
+];
+
 const normalizeUserMessageRenderingMode = (mode: unknown): 'markdown' | 'plain' => {
     return mode === 'markdown' ? 'markdown' : 'plain';
 };
 
-type VisibleSetting = 'sessionAssist' | 'sessionGoal' | 'theme' | 'windowControlsPosition' | 'pwaInstallName' | 'pwaOrientation' | 'mobileKeyboardMode' | 'timeFormat' | 'weekStart' | 'fontSize' | 'terminalFontSize' | 'terminalShell' | 'terminalLoginShell' | 'editorFontSize' | 'spacing' | 'inputBarOffset' | 'mermaidRendering' | 'userMessageRendering' | 'chatRenderMode' | 'messageTransport' | 'activityRenderMode' | 'collapsibleUserMessages' | 'stickyUserHeader' | 'promptNavigatorEnabled' | 'wideChatLayout' | 'codeBlockLineWrap' | 'splitAssistantMessageActions' | 'subagentReadOnlyBanner' | 'diffLayout' | 'mobileStatusBar' | 'dotfiles' | 'fileViewerPreview' | 'reasoning' | 'showToolFileIcons' | 'showTurnChangedFiles' | 'expandedTools' | 'followUpBehavior' | 'terminalQuickKeys' | 'fileEditorKeymap' | 'persistDraft' | 'inputSpellcheck' | 'reportUsage' | 'expandedEditorToolbar' | 'autoSaveEnabled';
+type VisibleSetting = 'sessionAssist' | 'sessionGoal' | 'theme' | 'windowControlsPosition' | 'pwaInstallName' | 'pwaOrientation' | 'mobileKeyboardMode' | 'timeFormat' | 'weekStart' | 'fontSize' | 'terminalFontSize' | 'terminalShell' | 'terminalLoginShell' | 'editorFontSize' | 'spacing' | 'inputBarOffset' | 'mermaidRendering' | 'userMessageRendering' | 'chatRenderMode' | 'messageTransport' | 'activityRenderMode' | 'collapsibleUserMessages' | 'stickyUserHeader' | 'promptNavigatorEnabled' | 'wideChatLayout' | 'codeBlockLineWrap' | 'splitAssistantMessageActions' | 'subagentReadOnlyBanner' | 'diffLayout' | 'mobileStatusBar' | 'dotfiles' | 'fileViewerPreview' | 'reasoning' | 'showToolFileIcons' | 'showTurnChangedFiles' | 'expandedTools' | 'followUpBehavior' | 'terminalQuickKeys' | 'fileEditorKeymap' | 'persistDraft' | 'inputSpellcheck' | 'largeTextPaste' | 'reportUsage' | 'expandedEditorToolbar' | 'autoSaveEnabled';
 
 const WINDOW_CONTROLS_POSITION_OPTIONS: Array<{ id: DesktopWindowControlsPosition; labelKey: string }> = [
     { id: 'left', labelKey: 'settings.openchamber.desktopNetwork.option.windowControlsLeft' },
@@ -372,6 +387,8 @@ export const OpenChamberVisualSettings: React.FC<OpenChamberVisualSettingsProps>
     const setPersistChatDraft = useUIStore(state => state.setPersistChatDraft);
     const inputSpellcheckEnabled = useUIStore(state => state.inputSpellcheckEnabled);
     const setInputSpellcheckEnabled = useUIStore(state => state.setInputSpellcheckEnabled);
+    const largeTextPasteBehavior = useUIStore(state => state.largeTextPasteBehavior);
+    const setLargeTextPasteBehavior = useUIStore(state => state.setLargeTextPasteBehavior);
     const showToolFileIcons = useUIStore(state => state.showToolFileIcons);
     const setShowToolFileIcons = useUIStore(state => state.setShowToolFileIcons);
     const showTurnChangedFiles = useUIStore(state => state.showTurnChangedFiles);
@@ -665,6 +682,7 @@ export const OpenChamberVisualSettings: React.FC<OpenChamberVisualSettingsProps>
         || shouldShow('reasoning')
         || shouldShow('followUpBehavior')
         || shouldShow('persistDraft')
+        || shouldShow('largeTextPaste')
         || shouldShow('showToolFileIcons')
         || shouldShow('expandedTools')
         || (!isMobile && shouldShow('inputSpellcheck'));
@@ -687,6 +705,7 @@ export const OpenChamberVisualSettings: React.FC<OpenChamberVisualSettingsProps>
         || shouldShow('dotfiles')
         || shouldShow('fileViewerPreview')
         || shouldShow('persistDraft')
+        || shouldShow('largeTextPaste')
         || shouldShow('showToolFileIcons')
         || shouldShow('showTurnChangedFiles')
         || (!isMobile && shouldShow('inputSpellcheck'))
@@ -2036,7 +2055,7 @@ export const OpenChamberVisualSettings: React.FC<OpenChamberVisualSettingsProps>
                                 </SettingsSection>
                                 )}
 
-                                {(shouldShow('persistDraft') || (!isMobile && shouldShow('inputSpellcheck'))) && (
+                                {(shouldShow('persistDraft') || shouldShow('largeTextPaste') || (!isMobile && shouldShow('inputSpellcheck'))) && (
                                 <SettingsSection
                                     title={t('settings.openchamber.visual.section.composer')}
                                     settingsItem="chat.composer"
@@ -2061,6 +2080,26 @@ export const OpenChamberVisualSettings: React.FC<OpenChamberVisualSettingsProps>
                                         settingsItem="chat.spellcheck"
                                     />
                                 )}
+
+                                {shouldShow('largeTextPaste') && (
+                                    <SettingsControlGroup
+                                        title={t('settings.openchamber.visual.field.largeTextPaste')}
+                                        info={t('settings.openchamber.visual.field.largeTextPasteHint')}
+                                        settingsItem="chat.large-text-paste"
+                                    >
+                                        <SettingsRadioGroup aria-label={t('settings.openchamber.visual.field.largeTextPasteAria')}>
+                                            {LARGE_TEXT_PASTE_BEHAVIOR_OPTIONS.map((option) => (
+                                                <SettingsRadioOption
+                                                    key={option.id}
+                                                    selected={largeTextPasteBehavior === option.id}
+                                                    onSelect={() => setLargeTextPasteBehavior(option.id)}
+                                                    label={tUnsafe(option.labelKey)}
+                                                    ariaLabel={t('settings.openchamber.visual.field.largeTextPasteOptionAria', { option: tUnsafe(option.labelKey) })}
+                                                />
+                                            ))}
+                                        </SettingsRadioGroup>
+                                    </SettingsControlGroup>
+                                )}
                                 </SettingsSection>
                                 )}
                             </>