refactor(desktop): large-paste writer in its own electron module, 3k threshold

Move writeComposerPaste out of electron/main.ts into composer-paste.ts
(placement gate: no new behaviour appended to the facade). Lower the
conversion threshold from 10k to 3k characters so a pasted stack trace or
log excerpt already becomes a chip. Trim the policy tests to two
invariants (strict threshold boundary; chip size label is byte-based) and
drop vendor references from code comments.

apps/desktop/electron/composer-paste.ts

@@ -0,0 +1,20 @@
+import crypto from 'node:crypto'
+import fs from 'node:fs'
+import path from 'node:path'
+
+/**
+ * Persist a large plain-text paste as a `.txt` file the composer can attach
+ * as a chip instead of flooding the input. The renderer never chooses the
+ * path: the file lands in a Desktop-managed directory with a generated name,
+ * mirroring how `writeComposerImage` handles pasted images.
+ */
+export async function writeComposerPaste(userDataDir: string, text: string): Promise<string> {
+  const dir = path.join(userDataDir, 'composer-pastes')
+  await fs.promises.mkdir(dir, { recursive: true })
+  const stamp = new Date().toISOString().replace(/[:.]/g, '-').replace('T', '_').replace('Z', '')
+  const random = crypto.randomBytes(3).toString('hex')
+  const filePath = path.join(dir, `pasted_content_${stamp}_${random}.txt`)
+  await fs.promises.writeFile(filePath, text, 'utf8')
+
+  return filePath
+}

apps/desktop/electron/main.ts

@@ -97,6 +97,7 @@ import {
 import { detectBundleSkew } from './bundle-skew'
 import { detectBundleSwap } from './bundle-swap'
 import { registerChatOnboardingWindow } from './chat-onboarding-window'
+import { writeComposerPaste } from './composer-paste'
 import { applyConnectionChange, teardownSshState } from './connection-apply'
 import {
   apiRequestRegistryConnectionId,
@@ -6298,20 +6299,6 @@ async function writeComposerImage(buffer, ext = '.png', name = '') {
   return filePath
 }
 
-// Large plain-text pastes are persisted as .txt files so the composer can
-// show them as an attachment chip instead of flooding the input (ChatGPT
-// Work-style large-paste handling). Mirrors writeComposerImage above.
-async function writeComposerPaste(text) {
-  const dir = path.join(app.getPath('userData'), 'composer-pastes')
-  await fs.promises.mkdir(dir, { recursive: true })
-  const stamp = new Date().toISOString().replace(/[:.]/g, '-').replace('T', '_').replace('Z', '')
-  const random = crypto.randomBytes(3).toString('hex')
-  const filePath = path.join(dir, `pasted_content_${stamp}_${random}.txt`)
-  await fs.promises.writeFile(filePath, text, 'utf8')
-
-  return filePath
-}
-
 function previewLabelForUrl(url) {
   return `${url.host}${url.pathname === '/' ? '' : url.pathname}`
 }
@@ -17038,7 +17025,7 @@ ipcMain.handle('hermes:savePastedText', async (_event, payload) => {
     throw new Error('savePastedText: missing text')
   }
 
-  return writeComposerPaste(text)
+  return writeComposerPaste(app.getPath('userData'), text)
 })
 
 ipcMain.handle('hermes:saveClipboardImage', async () => {

apps/desktop/src/app/chat/composer/index.tsx

@@ -564,8 +564,8 @@ export function ChatBar({
 
     event.preventDefault()
 
-    // ChatGPT Work-style large-paste handling: a paste past the threshold
-    // becomes a `.txt` attachment chip instead of flooding the composer.
+    // A paste past the large-paste threshold becomes a `.txt` attachment chip
+    // instead of flooding the composer.
     // The instruction the user types stays in the input; the pasted source
     // material rides along as a file. Falls back to inline insertion if the
     // attachment can't be created (missing bridge, write failure) so the

apps/desktop/src/app/chat/composer/large-paste.test.ts

@@ -1,33 +1,16 @@
 import { describe, expect, it } from 'vitest'
 
-import { LARGE_PASTE_ATTACHMENT_THRESHOLD, shouldConvertPasteToAttachment } from './large-paste'
+import { LARGE_PASTE_ATTACHMENT_THRESHOLD, pasteSizeLabel, shouldConvertPasteToAttachment } from './large-paste'
 
-describe('shouldConvertPasteToAttachment', () => {
-  it('keeps short pastes inline', () => {
-    expect(shouldConvertPasteToAttachment('hello world')).toBe(false)
-    expect(shouldConvertPasteToAttachment('')).toBe(false)
-  })
-
-  it('keeps a paste exactly at the threshold inline', () => {
+describe('large paste policy', () => {
+  it('converts only pastes strictly past the threshold', () => {
     expect(shouldConvertPasteToAttachment('a'.repeat(LARGE_PASTE_ATTACHMENT_THRESHOLD))).toBe(false)
-  })
-
-  it('converts a paste one character past the threshold', () => {
     expect(shouldConvertPasteToAttachment('a'.repeat(LARGE_PASTE_ATTACHMENT_THRESHOLD + 1))).toBe(true)
-  })
-
-  it('honors a custom threshold', () => {
-    expect(shouldConvertPasteToAttachment('abcdef', 5)).toBe(true)
-    expect(shouldConvertPasteToAttachment('abcde', 5)).toBe(false)
-  })
-
-  it('never converts when the threshold is disabled (non-positive)', () => {
     expect(shouldConvertPasteToAttachment('a'.repeat(50_000), 0)).toBe(false)
-    expect(shouldConvertPasteToAttachment('a'.repeat(50_000), -1)).toBe(false)
   })
 
-  it('rejects non-string input defensively', () => {
-    expect(shouldConvertPasteToAttachment(undefined as unknown as string)).toBe(false)
-    expect(shouldConvertPasteToAttachment(null as unknown as string)).toBe(false)
+  it('labels the chip by encoded byte size, not character count', () => {
+    expect(pasteSizeLabel('a'.repeat(512))).toBe('512 B')
+    expect(pasteSizeLabel('\u00e9'.repeat(1024))).toBe('2.0 KB')
   })
 })

apps/desktop/src/app/chat/composer/large-paste.ts

@@ -1,15 +1,14 @@
 /**
  * Large-paste-to-attachment policy.
  *
- * Inspired by ChatGPT Work's composer behavior (OpenAI release notes,
- * Aug 4 2026): pasting more than ~10k characters converts the content into a
- * text attachment instead of inserting it inline, keeping the composer clean
- * and preventing a single paste from flooding the input. Short pastes stay
- * inline; the threshold lives here so every paste handler shares one policy.
+ * Pasting more than ~3k characters converts the content into a text
+ * attachment instead of inserting it inline, keeping the composer clean and
+ * preventing a single paste from flooding the input. Short pastes stay inline;
+ * the threshold lives here so every paste handler shares one policy.
  */
 
 /** Characters beyond which a plain-text paste becomes a `.txt` attachment. */
-export const LARGE_PASTE_ATTACHMENT_THRESHOLD = 10_000
+export const LARGE_PASTE_ATTACHMENT_THRESHOLD = 3_000
 
 /**
  * True when a plain-text paste should be converted into a text attachment

apps/desktop/src/app/chat/hooks/use-composer-actions.ts

@@ -591,8 +591,8 @@ export function useComposerActions({
   )
 
   /**
-   * Convert a very large plain-text paste into a `.txt` attachment chip
-   * (ChatGPT Work-style). The exact pasted text is written to a
+   * Convert a very large plain-text paste into a `.txt` attachment chip.
+   * The trimmed, sanitized paste text is written to a
    * Hermes-managed composer-pastes file via the main process, then attached
    * through the same `@file:` pipeline as a manually attached text file.
    * Returns false (paste stays inline) when the desktop bridge is missing

apps/desktop/src/app/chat/index.tsx

@@ -759,8 +759,8 @@ const ChatViewContent = memo(function ChatViewContent({
               onAddUrl={onAddUrl}
               onAttachDroppedItems={onAttachDroppedItems}
               onAttachImageBlob={onAttachImageBlob}
-              onAttachPrCommentUrl={onAttachPrCommentUrl}
               onAttachPastedText={onAttachPastedText}
+              onAttachPrCommentUrl={onAttachPrCommentUrl}
               onCancel={onCancel}
               onPasteClipboardImage={onPasteClipboardImage}
               onPickFiles={onPickFiles}

apps/desktop/src/app/chat/session-tile.tsx

@@ -307,8 +307,8 @@ function TileChat({
           onAddUrl={onAddUrl}
           onAttachDroppedItems={composer.attachDroppedItems}
           onAttachImageBlob={composer.attachImageBlob}
-          onAttachPrCommentUrl={composer.attachPrCommentUrl}
           onAttachPastedText={composer.attachPastedText}
+          onAttachPrCommentUrl={composer.attachPrCommentUrl}
           onCancel={actions.cancelRun}
           onDeleteSelectedSession={noop}
           onDismissError={actions.dismissError}