Kitty: malformed OSC 9 notification '4;0;' emitted on /exit

Description

Every time Claude Code exits (via /exit or /quit), it sends a malformed OSC 9 (ConEmu-style) notification to the terminal. In Kitty, this renders as a desktop notification with the body 4;0;.

Root Cause

Captured via Python pty, the exact byte sequence emitted at exit is:

\e]9;4;0;\a

This is an OSC 9 notification where the payload appears to be structured as <type>;<code>;<message> — but the <message> field is empty. Kitty has no message to display, so it renders the raw parameters (4;0;) as the notification body.

Steps to Reproduce

1. Run claude in Kitty terminal (v0.32.2, Linux)
2. Type /exit or /quit
3. A Kitty desktop notification appears immediately with body 4;0;

This happens on every exit.

Environment

• Claude Code: v2.1.126
• Terminal: Kitty 0.32.2
• OS: Ubuntu (Linux 6.17.0)
• TERM: xterm-kitty
• KITTY_WINDOW_ID is set (Claude Code detects Kitty)

Captured Evidence

Python pty capture (hex), offset 0x4e0 — the exit sequence:

000004e0: 5b72 1b38 1b5d 393b 343b 303b 071b 5d30  [r.8.]9;4;0;..]0
000004f0: 3b07                                     ;.

Decoded: \e[r (reset scroll region), \e8 (restore cursor), \e]9;4;0;\a (malformed notification), \e]0;\a (clear window title).

Expected Behavior

Either:

• The notification body should contain a meaningful message (e.g. "Session ended"), or
• The OSC 9 notification should not be emitted on exit at all

Workaround

None available on the Kitty side — Kitty 0.32.2 does not expose per-protocol notification suppression. Fix needs to be in Claude Code's exit/cleanup sequence.