Large paste truncated in Claude Code / Copilot sessions — only last lines appear

[itai-hania]

Bug Description

When pasting multi-line text (50+ lines) into an active AI session (Claude Code or GitHub Copilot), only the last few lines are pasted. The first lines are silently dropped. Pasting the same content into a new terminal (inside or outside tmax) works fine.

Steps to Reproduce

1. Open tmax on Windows
2. Start a Claude Code or GitHub Copilot session
3. Copy 50 lines of text to the clipboard
4. Paste into the AI session (Ctrl+V or right-click)
5. Observe that only the last few lines appear

Expected Behavior

All copied lines should be pasted into the session.

Actual Behavior

The beginning of the pasted text is silently truncated. Only the tail end appears.

What Works

• Pasting the same content into a new tmax terminal — ✅ works
• Pasting the same content into a terminal outside tmax — ✅ works
• Only fails in active AI sessions (Claude Code, Copilot)

Root Cause Analysis

AI sessions (Claude Code, Copilot) enable bracketed paste mode (\x1b[?2004h). When tmax detects this, it wraps the entire pasted text in bracketed paste escape sequences and sends it as a single write:

src/renderer/components/TerminalPanel.tsx (lines 549–559):

if (cursorHideSignalsRef.current.bracketedPaste) {
  text = `\x1b[200~${text}\x1b[201~`;
}
window.terminalAPI.writePty(terminalId, text);

src/main/pty-manager.ts (line ~200):

pty.write(data);  // entire bracketed paste in one shot

The entire payload — escape sequences + 50 lines of text — is sent as a single pty.write() call. Windows ConPTY or the receiving application's input processing truncates the beginning when the payload is too large, keeping only the tail.

New terminals work because they don't have bracketed paste mode enabled, so the shell's default input handling (which is more tolerant of large input) processes the paste.

Suggested Fix

Chunk large writes in PtyManager.write() when the payload exceeds a threshold:

1. Split writes larger than ~4KB into sequential chunks
2. Add a small delay between chunks to allow ConPTY / the receiving application to process each one
3. Keep the bracketed paste wrapper on the first and last chunks respectively (\x1b[200~ on first, \x1b[201~ on last)
4. Keep single-keystroke writes unchanged for responsiveness

Environment

• OS: Windows 11
• tmax version: latest

[itai-hania]

Opened the bug and actively working on fixing it
CC @InbarR

[InbarR]

Thanks for the detailed write-up @itai-hania - the symptom you described (last lines only, only in active AI sessions) is exactly what we hit, and your repro lined up with our investigation.

Root cause was actually upstream of the chunking suggestion: AI sessions (Claude Code, Copilot CLI, PSReadLine) enable bracketed paste mode (?2004h), and the paste handler was sending the payload without the \x1b[200~ / \x1b[201~ wrappers - so each embedded \n was interpreted by the shell as Enter, submitting earlier lines one-by-one until only the last segment remained at the live prompt. Claude Code now correctly receives multi-line pastes as a single payload (rendered as [Pasted text #1 +N lines]).

Fixed across all four paste entry points:

• Ctrl+V in the main window: 16631ee (in v1.6.0)
• Right-click paste in the main window, plus Ctrl+V and right-click in detached terminal windows: follow-up coming in the next release - extracted the wrap into a pure helper (prepareClipboardPaste) so all four paths share the same logic
• Regression test added: tests/e2e/paste-wrap.spec.ts (8 cases pinning down wrap-on-bracketed, raw-when-disabled, CRLF/CR normalization, and a 60-line release-notes-sized payload)

Closing as fixed. If you upgrade to the next release and still see truncation in any specific paste flow, please reopen with the trigger details (Ctrl+V vs right-click vs Edit menu, main window vs detached) and we'll dig back in.