ADR 0008 — The policy seat: ship the router, leave room for the rest

Status: accepted · Date: 2026-09-19 · Sprint: 1

Context

The paper states the RL router “is reported only for completeness; its paired tests show no significant improvement and it is not claimed as a contribution.” That is an honest result. It is also explainable: the current agent is a linear softmax over six hand-made features with four actions, trained on a small episode file, with abstention applied downstream as a threshold rather than learned.

Decision

DecisionPolicy is a port. The supervised router ships as the default, because it is the configuration that works today. Two further seats exist and stay empty in this deliverable:

• a contextual bandit (LinUCB / Thompson) over the confidence signal vector — most of this problem is contextual rather than sequential, and a bandit would come with a regret bound the RL policy does not have
• an offline RL policy with ABSTAIN as a first-class action and reward r = 1{correct} − λ·1{wrong} + 0·1{abstain}, λ > 1, so the risk–coverage trade-off is learned rather than applied afterwards

Two architectural choices make those seats usable later: the policy’s observation is the confidence signal vector rather than six hand-made features, and ABSTAIN is expressible as an action rather than only as a downstream threshold.

Scope

No policy evaluation happens in this deliverable. No off-policy estimation, no significance testing. The seven evaluation modes stay runnable with a smoke test each, because they are part of what CE-RISE is being handed.

Consequences

• A later attempt at the policy question starts from the right interface instead of a refactor. The published “no significant improvement” result is worth revisiting, and the changes that would make it worth revisiting are structural.
• The routing gap the paper names (COMPASS 0.7085 vs Sym-Only 0.9051 on logic) is addressable by a policy that can see the symbolic fire signal — which this observation space provides. − Two empty seats in the codebase. They cost a Protocol and a docstring.