Similarity ladder and recovery-quality policy

DEC-0019 - Similarity ladder and recovery-quality policy

Context

Need concrete execution rules for “similar exercise” so cooldown-reset logic is predictable and learner-friendly.

Decision

Similarity matching uses fallback ladder:

1. A (strict): same program + same skill + same exercise type + difficulty delta <= 1.
2. B (medium): same program + same skill.
3. C (broad): same skill. System tries A first, then B, then C only when higher tier candidates are unavailable.

Recovery validity principle:

• Avoid rigid per-item hard gates based on raw time or per-item question count.
• Use soft quality conditions based on:
  • practice time,
  • completion ratio per exercise.
• Recovery is counted when learner completes at least one similar exercise and passes configured quality thresholds.

Async scoring rule (Writing/Speaking):

• Cooldown reset is applied only after scoring is completed.

Reset scope:

• Cooldown reset is scoped by skill within program.

Rationale

The ladder balances relevance and coverage. Soft quality conditions reduce mechanical behavior while avoiding overly strict user friction. Async-scored skills need result-ready confirmation before counting recovery. Skill-within-program scope prevents over-resetting unrelated learning areas.