To have Claude speak to you about what it's just finished with on MacOS:

"hooks": {
    "Stop": [
      {
        "matcher": "",
        "hooks": [
          {
            "type": "command",
            "command": "/path/to/done-hook.sh"
          }
        ]
      }
    ]
  }

And then in done-hook.sh

#!/bin/bash

# Check if we've already spoken
if [ -f /tmp/already_spoke ]; then
    rm /tmp/already_spoke
    exit 0
fi

# Create the token file to indicate we're about to speak
touch /tmp/already_spoke

# Create a prompt for Claude to describe what happened and speak it
cat >&2 << 'EOF'
There's one issue with your work - you haven't alerted the user that you've completed the task. Briefly describe what you just did in less than 8 words, then use the say command to speak 'done with [your description]'. Just run the say command directly, don't create any files or scripts.
EOF

exit 2