aI'm Thinking plays typing sounds for Claude Code, Codex

The app is built as two layers: a Swift menu-bar front end that plays sounds and a Rust core that watches files and infers state. The Rust side emits only small NDJSON activity messages, such as a phase and an intensity value, and the Swift side turns that into taps, so the sound layer never reads logs and the log parser never plays audio. Rather than firing a tap per event, it treats events as impulses that decay over time and takes the maximum before smoothing, rising fast and falling slowly to mimic a person starting to type and then pausing.

The hardest part was timing. Claude Code writes its JSONL after an API message completes, so a log line describes what just finished rather than what is happening now. The developer measured a median 5 seconds, p90 33 seconds, and a maximum 59 seconds between a prompt or tool result and the next line, which would make the most intense thinking the quietest period. The fix sets a waiting flag when a prompt is sent or tools return and keeps tapping until the next line arrives, holding for 60 seconds and fading out at 120 seconds based on those measurements. A separate bug, where pressing Esc left the app tapping for up to 2 minutes, was resolved by watching the busy/idle status in ~/.claude/sessions/<pid>.json.