Simple threshold model and scale guardrails

DEC-0020 - Simple threshold model and scale guardrails

Context

Need to lock a practical execution model that stays understandable to learners while remaining scalable for product operation.

Decision

Threshold model (simple core):

• Practice-time threshold is configured by skill.
• Completion-ratio threshold is configured by exercise family:
  • objective,
  • subjective.

Fallback quality guardrails:

• Tier C fallback is allowed only when A/B candidate inventory is below minimum.
• Tier C fallback cannot cross program boundaries, even when skill matches.

Recovery reset strictness:

• One qualifying similar exercise is enough to reset cooldown.
• No additional chain requirement (no 2-step/3-step mandatory recovery chain).

Simplicity and scale constraints:

• Do not introduce per-program or per-level threshold branching in the core rule at this stage.
• Keep initial configuration compact and centrally managed.

Rationale

This model keeps learner-facing behavior simple and predictable while limiting operational complexity. It preserves quality via ladder guardrails without turning recovery into a strict or confusing process.