/copy inside tmux: OSC52 wrapped in DCS passthrough — content lost ("unverified") in tmux buffer and never reaches outer terminal

Environment

• Kimi Code 0.38.0, Linux x86_64 server over SSH from a macOS client running Zellij
• tmux 3.4 with set-clipboard on
• Outer terminal: Zellij on macOS

Summary

When running Kimi Code inside tmux, /copy emits an OSC 52 sequence wrapped in a tmux DCS passthrough (ESC P tmux; … ESC \). This breaks both directions:

1. tmux side: with set-clipboard on, tmux sees the sequence but reports it "unverified" and stores no payload — tmux show-buffer shows only Copied via terminal escape sequence (unverified, 4117 characters). with the actual text lost. Pasting in another tmux window (prefix + ]) yields nothing.
2. Outer terminal side: the wrapped sequence is also not delivered — nothing lands in the local macOS clipboard (verified via Zellij).

Reproduction

1. Inside tmux: run kimi, send any message (e.g. reply with exactly: KIMI-CLIP-TEST-OK), wait for the reply.
2. Run /copy.
3. tmux list-buffers / tmux show-buffer → buffer contains only the unverified annotation line, no content.

Root cause (from bundled binary, clipboard-osc52.ts)

function buildClipboardOSC52(text, insideTmux = isInsideTmux()) {
  const sequence = `${ESC}]52;c;${Buffer.from(text, "utf8").toString("base64")}${BEL}`;
  if (!insideTmux) return sequence;
  return `${ESC}Ptmux;${sequence.replaceAll(ESC, `${ESC}${ESC}`)}${ESC}${ST}`;
}

The ESC P tmux; prefix is the tmux passthrough convention (forward verbatim to the parent terminal, bypassing tmux's own handling). Two consequences:

• tmux 3.4 still observes the inner OSC 52 and tries to decode it, fails, and stores only an annotation → content lost even with set-clipboard on.
• The passthrough skips tmux entirely, so in SSH setups (tmux on server, emulator on client) delivery depends wholly on the client; in our case (Zellij on macOS) it doesn't arrive.

Expected behavior

Other tools handle this correctly: Claude Code and yazi emit a plain, unwrapped OSC 52 (ESC ]52;c;<base64> ESC \). tmux then writes it to the buffer (paste anywhere with prefix + ]) and forwards it to the parent terminal. Please emit the unwrapped sequence inside tmux too, or make the passthrough compatible with tmux 3.x.

Workaround

Mouse selection + tmux copy-mode; or another tool whose copy works inside tmux.

Inspect the bundled clipboard-osc52.ts implementation and the /copy entry point, then reproduce the issue with tmux set-clipboard on. Verify that the emitted OSC 52 sequence is handled by tmux and reaches the outer terminal, with the full text present in tmux show-buffer and the local clipboard.