Mastery, growth, and cross-session tracking

[satra]

Summary

Implement mastery, growth, and cross-session tracking for KIVA learners so the platform can estimate exposures per word, instructional effort, time to mastery, retention, and longer-term growth.

Scope

• define word exposure and mastery state transitions
• aggregate instructional effort and practice attempts per target word
• compute time-to-mastery and retention metrics across sessions
• support learner-linked longitudinal summaries where identity linkage is available
• expose interpretable summaries for product, research, and evaluation use

Deliverables

• mastery metric definitions
• cross-session aggregation jobs or services
• learner-level summary outputs
• session and longitudinal summary generation hooks

Testing

• metric derivation tests on fixed fixtures
• cross-session aggregation tests
• regression tests for mastery state transitions

Dependencies

• depends on event pipeline and contracts