[R9.1] Why mode for Bering-based gate decisions

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Context

Epic: R9. UX and explainability

Scope

Implement a "why" mode that explains Sheaft decisions using endpoint paths, thresholds, and referenced Bering model evidence.

Definition of Done

For each elevated risk, output top evidence items with confidence and policy rationale.

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Progress update (March 3, 2026)

Status: Not started (0%)

Implemented so far

• No full evidence-driven "Why" mode implemented yet.

Remaining to close this issue

• Implement per-risk evidence explanations and confidence decomposition.

[a-a-k]

Second-pass pivot update (March 3, 2026): status = planned. Why-mode evidence output is not implemented yet.