Scrollback history lost when pasting large text in terminal

[waleedkadous]

Summary

When pasting a large chunk of text into the dashboard terminal and scrolling up, the beginning of the pasted text is not visible. Scrollable history is being lost.

Current Architecture

Browser (xterm.js) ←→ WebSocket ←→ Tower (node-pty) ←→ tmux session ←→ shell/claude

Current buffer sizes

• xterm.js scrollback: 10,000 lines (Terminal.tsx:42)
• tmux history-limit: not set (default: 2,000 lines)
• Server RingBuffer: 1,000 lines (tower-server.ts:364)

Current tmux config (per session)

• alternate-screen off — tmux writes to normal buffer so xterm.js native scroll works
• mouse off — xterm.js handles selection and clipboard
• status off — dashboard has its own tabs
• No history-limit set

Root Cause Analysis

The most likely culprit is tmux's default history-limit of 2,000 lines. Even with alternate-screen off, tmux manages its own internal buffer. However, since alternate-screen is off, xterm.js should be receiving all output in its normal buffer (10,000 line scrollback). Possible causes:

1. tmux history-limit too small (2,000 default) — may affect output flow
2. RingBuffer too small (1,000 lines) — affects replay on reconnect
3. xterm.js scrollback may need increase for heavy use
4. Possible \x1b[3J (clear scrollback) sequences from applications inside tmux

CRITICAL: Read Before Fixing

Read codev/resources/terminal-tmux.md in its entirety before making ANY changes. This area has wasted 10+ hours on previous bugs. Rules:

1. Never quick-fix Terminal.tsx — understand the full architecture first
2. Intermittent = external state mutation — grep for all code touching tmux options
3. tmux -g is GLOBAL — always use -t <session> for per-session settings
4. Test after changes — build, install, restart Tower, verify in dashboard

Proposed Fix (Conservative)

1. Set tmux history-limit to 50,000 on session creation (tower-server.ts ~line 572)
2. Set tmux history-limit to 50,000 on session reconnection (~line 810)
3. Increase RingBuffer from 1,000 to 10,000 lines (tower-server.ts:364)
4. Increase xterm.js scrollback from 10,000 to 50,000 (Terminal.tsx:42)

Key Files

File	Role
packages/codev/dashboard/src/components/Terminal.tsx	xterm.js setup, scrollback config
packages/codev/src/agent-farm/servers/tower-server.ts (~line 572)	tmux session creation
packages/codev/src/agent-farm/servers/tower-server.ts (~line 810)	tmux session reconnection
packages/codev/src/terminal/pty-session.ts	RingBuffer initialization
codev/resources/terminal-tmux.md	READ THIS FIRST

[waleedkadous]

On it! Working on a fix now.