Implement terminal streaming with diff algorithm

[2witstudios]

Epic 4: WebSocket & Real-Time Push — Issue 3/3

Source: 3-agent worktree — best terminal diff algorithm (longest common suffix)

Description

Per-agent terminal output streaming over WebSocket with efficient diff algorithm that only sends new lines.

Acceptance Criteria

• Per-agent subscriptions with lazy initialization
• 500ms polling interval for tmux pane content
• Longest common suffix diff algorithm — only sends new lines, not full buffer
• Shared timer across clients watching the same agent (don't poll twice)
• Auto-cleanup when subscriber count drops to 0
• Error handling for dead/missing panes
• Tests: diff algorithm, subscription lifecycle, shared timer, cleanup

Dependencies

• Requires: Implement WebSocket handler and event system #73 (WebSocket handler)

Files to Create/Modify

• src/server/ws/terminal.ts (new)
• src/server/ws/terminal.test.ts (new)