echo-cue 🔔 (a.k.a. "echo")

A zero-build local patch for OpenClaw Control UI (webchat) that plays a short two-tone chime (A5 → E5, ~900ms) when an assistant reply finishes streaming. Designed as a stop-gap until upstream PR openclaw/openclaw#73894 (issue #69186) lands.

Why this exists

OpenClaw Control UI has no completion sound on main yet. PR #73894 implements it but has been OPEN without review since 2026-04-29. This skill injects an equivalent IIFE into the bundled UI dist so it works today, and gracefully steps aside when upstream ships.

What you get

• Short ding-dong when the assistant finishes a reply
• Skipped for NO_REPLY / empty silent completions
• Always rings by default (foreground + background); set onlyHidden=on to limit to hidden tabs only
• 4-second hard rate-limit + content-fingerprint dedup → never double-rings on streaming re-renders
• Per-browser localStorage toggles (no UI surface added)
• One-shot apply / remove with backup
• Cache-bust: rewrites index.html to a new bundle filename so plain Cmd+R picks up the patch
• Patches every detected OpenClaw install (brew + nvm + OPENCLAW_HOME) so it works even when Gateway runs under a different node than which openclaw resolves
• Auto-detects upstream PR landing → skips itself

Install

bash apply.sh

Then refresh your Control UI browser tab (regular Cmd+R is enough, the script cache-busts the bundle filename). Click or press a key once on the page to unlock the AudioContext (this happens automatically the first time you send a message).

Verify

DevTools console:

window.__milly_cue_v1__   // → true

Send a question, switch to another tab — you should hear a ding-dong when the assistant finishes.

Toggle (per browser)

// Disable entirely
localStorage.setItem('milly.completionCue', 'off')

// Re-enable
localStorage.removeItem('milly.completionCue')

// Ring even when the tab is in foreground (default behaviour as of 0.2.0):
localStorage.removeItem('milly.completionCue.onlyHidden')

// Limit ringing to hidden / unfocused tabs only:
localStorage.setItem('milly.completionCue.onlyHidden', 'on')

Uninstall

bash remove.sh

Restores the original bundle from index-*.js.milly.bak and the original index.html from index.html.milly.bak.

After openclaw update

The update overwrites dist/control-ui/..., dropping the patch. Re-run:

bash apply.sh

apply.sh is idempotent and detects upstream:

• Already patched → skip
• Upstream responseCompletionSound shipped → skip + advise uninstall

Known limits

• Anchor: .chat-group.assistant DOM class. If OpenClaw renames it the patch silently does nothing (fail-quiet, no breakage).
• AudioContext requires one user gesture per page load (browser policy).
• Webchat only. TUI / iOS / macOS / Android clients are not covered (they have their own native notification stacks).
• Single audible cue per assistant turn regardless of message length.

File layout

Related

• Issue: openclaw/openclaw#69186
• Upstream PR (stop-gap target): openclaw/openclaw#73894
• Sibling skill (same pattern): agent-tab-title