[jung-thomas]

Summary

The event display-app's content views ("Most Popular Tracks", "Finished by Topic", "Who's on Fire", "Topic Distribution", Activity Ticker) showed the wrong labels — rows like "1 tutorial / 2 tutorials / 3 tutorials" instead of real names.

Root cause: getEventBuckets returned a per-attendee completion histogram, but every display consumer (socket keying, DonutChart, TrendingView, both leaderboards, ticker) is written to render completions grouped by name. Two incompatible groupings shared one buckets array. The earlier date-window fix populated the (mis-shaped) histogram, surfacing the mismatch.

Fix: group buckets by track = CompletionPaths under the event's mission — the same resolution the app-space page uses. No new grouping invented.

event → mission (Events.mission_ID, else Missions.event_ID backlink)
      → CompletionPaths  (each = one track, label = CompletionPaths.name)
      → completions matched via CompletionPathItems (+ GroupPathItems for GROUP items)

Window-scoped to [startDate,endDate]; distinct users per track.

Changes

• srv/lib/event-path-buckets.js (new) — single source of truth. computePathBuckets() + trackNamesForTutorial() + shared resolveEventMissionId()/buildTrackMap() helpers.
• srv/event-stream-service.js (anonymous display) — getEventBuckets → computePathBuckets.
• srv/display-service.js (authed admin) — same fix; it had the identical event_ID-always-NULL bug (returned []).
• srv/developer-service.js (realtime socket) — live completions now labeled with their track name(s) in the active event's mission (one emit per track), replacing primaryTag keying that never matched bucket names. Completions outside every track emit nothing.

Verification

• 44 unit tests pass (new event-path-buckets.test.js incl. GROUP-expansion + distinct-user counting; updated event-stream + display-service specs).
• Probed PROD event 10000002: returns real tracks ("ABAP":2, "Joule Studio":1), resolved via the Missions.event_ID backlink (the event's mission_ID is NULL — the known FK trap, handled).

Test plan

• Deploy to DEV, load display-app against event 10000002, confirm track-named bars across all views + live increments land in the right bar