Timer reach metric: attach audience_size to timer_started events #107

Goal

Measure timer reach — how many meeting participants the timer serves — instead of only counting operator starts. A class with 20 people where the teacher starts the timer 15 times currently looks identical to 15 solo web starts.

Proposed client change

In apps/zoom-app/src/components/LiveTab.jsx, attach the meeting headcount to the timer_started event:

1. Import the existing hook: import useZoomParticipants from '../hooks/useZoomParticipants';
2. Call it alongside the other hooks: const { participants: meetingParticipants, restricted: participantsRestricted } = useZoomParticipants();
3. Add to the timer_started properties:

...(!participantsRestricted && meetingParticipants.length > 0
  ? { audience_size: meetingParticipants.length }
  : {}),

Full diff is in ~/workspace/goals/hone-my-tech-products-and-services/files/timer-reach-audience-size.patch (Jarvis workspace).

Privacy

Count only — participant names never leave the device. The property is omitted (not zeroed) when:

• the web version (no Zoom SDK), or
• the participant list is withheld (non-host/co-host), where the list may contain only self.

Analytics treats missing as reach of 1 (the operator), which is a defensible lower bound.

Analytics side (already done)

• Daily/weekly traffic report (traffic_report.py): new "Timer reach" line = sum of per-meeting max audience_size per day (grouped by zoom_meeting_id, falling back to distinct_id; 15 starts in one class count once). Shows n/a until the client ships.
• PostHog dashboard "Toastmusters Traffic" + saved insight "Timer reach (daily)".

No backfill possible — data starts when the instrumented build deploys.

Acceptance

• Host/co-host starts timer in a meeting → timer_started carries audience_size = full participant count
• Non-host starts timer → property absent
• Web timer start → property absent
• PostHog "Timer reach (daily)" insight starts showing reach > starts once deployed