SubMiner/backlog/tasks/task-193 - Fix-session-chart-event-popup-position-drift.md

id, title, status, assignee, created_date, updated_date, labels, milestone, dependencies, references, priority, ordinal

id	title	status	assignee	created_date	updated_date	labels	milestone	dependencies	references	priority	ordinal
TASK-193	Fix session chart event popup position drift	Done	Codex	2026-03-17 23:55	2026-03-17 23:59	stats ui bug	m-1		stats/src/components/sessions/SessionDetail.tsx stats/src/components/sessions/SessionEventOverlay.tsx stats/src/lib/session-events.ts	medium	105600

Description

Fix the session timeline event popup trigger positions so hover markers stay aligned with the underlying chart event lines across the full visible time range.

Acceptance Criteria

• #1 Event popup triggers stay horizontally aligned with chart event lines from session start through session end.
• #2 Alignment logic uses the rendered chart plot area rather than guessed container percentages.
• #3 Regression coverage locks the marker-position projection math.

Implementation Plan

1. Add a failing regression test for marker-position projection with chart offsets.
2. Capture the rendered plot box from Recharts and pass it into the overlay.
3. Position overlay markers in plot-area pixels, rerun targeted stats verification, then record the result.

Outcome

Completed. Session event hover markers now read the actual Recharts plot-area offset and width, then project marker X positions into plot-area pixels instead of full-container percentages. That keeps popup triggers aligned with the underlying reference lines across long session timelines.

Verification:

• bun test stats/src/lib/session-events.test.ts stats/src/lib/session-detail.test.tsx stats/src/components/sessions/SessionEventPopover.test.tsx
• cd stats && bun run build
• bun x prettier --check 'stats/src/components/sessions/SessionDetail.tsx' 'stats/src/components/sessions/SessionEventOverlay.tsx' 'stats/src/lib/session-events.ts' 'stats/src/lib/session-events.test.ts' 'backlog/tasks/task-193 - Fix-session-chart-event-popup-position-drift.md'
• bun run typecheck:stats still fails on pre-existing unrelated errors in src/components/anime/AnilistSelector.tsx, src/components/library/LibraryTab.tsx, src/lib/reading-utils.test.ts, src/lib/reading-utils.ts, src/lib/vocabulary-tab.test.ts, and src/lib/yomitan-lookup.test.tsx