[Bug] Rising algorithm inflates scores for new storylines with no prior history

[realproject7]

Bug

In lib/ranking.ts, the rising algorithm computes acceleration = recentScore / priorScore. When a storyline has zero prior window activity, priorScore approaches 0, causing acceleration to inflate to extreme values. New storylines with any recent activity will always dominate the rising tab.

Impact: Rising tab is dominated by brand-new storylines regardless of actual acceleration, making it useless for discovering genuinely accelerating content.

Fix:

• Add a minimum threshold for priorScore (e.g., if priorScore < threshold, exclude from rising or cap the acceleration ratio)
• Alternatively, require a minimum age (e.g., storyline must be older than the prior window) to appear in rising
• Consider a minimum activity threshold (e.g., at least N ratings or plots in prior window)

Context: Introduced in PR #86. The filter trendScore > 1 (line ~245) does not prevent this — it just checks recent > prior, not the magnitude.

Checklist:

• Add minimum prior activity threshold for rising candidates
• npm run lint and npm run typecheck pass

Labels: bug, agent/T3