Behavioral baseline learning for agent skills

[arkavo-com]

Spec scenario: SEQ-005

Gap: LearningModule tracks per-agent Thompson Sampling statistics but has no concept of behavioral baseline — no way to capture typical action sequences, extract frequency distributions, or compare current vs baseline.

RED test: crates/arkavo-router/tests/sequence_integrity_test.rs

• learning_module_has_no_baseline_capture — FAILS

Required changes (in crates/arkavo-router/src/learning/):

• Add baseline capture from session history
• Add baseline comparison method
• Add strict mode for cold start (insufficient history)

Refs: specs/arkavo-edge/sequence-integrity.spec.yaml