drive_situation_fusion #

The seam that supplies compound_failure_advisor from the signals the SNGNav catalog already produces.

compound_failure_advisor is deliberately zero-dependency — it mirrors the enum shapes it needs so it never inherits a runtime dependency tree and stays 32-bit-ARM friendly. The price of that decoupling is a seam: someone has to map localization_fallback's LocalizationMode onto the advisor's PositionTrust, and condition_aggregator's AdvisorySeverity onto AdvisoryLevel. This package is that seam — done once, correctly, and tested — so no integrator re-derives it, and no integrator can get the one safety-critical case wrong.

The safety-critical case #

LocalizationMode.deadReckoning — GPS is gone and the dot is being carried by dead reckoning with a growing confidence radius — maps to PositionTrust.degraded, not trusted. A hand-mapping that treats "still emitting a position" as trusted would silently suppress the compound caution at the exact moment she has lost GPS in snow — the compound-failure scenario the advisor exists for. This package makes that mapping canonical.

Use #

import 'package:compound_failure_advisor/compound_failure_advisor.dart';
import 'package:drive_situation_fusion/drive_situation_fusion.dart';

// `estimate` from localization_fallback; `advisory` the single most-severe
// in-area advisory you already selected from condition_aggregator; visibility
// from your live weather source (you own the clock, so you pass the age).
final situation = fuseDriveSituation(
  estimate: estimate,
  advisory: advisory,               // or null — "no advisory in force"
  visibilityMeters: observation.meters,
  visibilityAgeSeconds:
      now.difference(observation.measuredAt).inSeconds.toDouble(),
  speedMetersPerSecond: speed,
);

final advice = adviseInDrive(situation); // advisory-only; she drives it.

Contract #

Pure Dart. Total and deterministic — like the advisor it feeds, it never throws, owns no clock, and does no IO. It maps values across the advisor's zero-dependency seam and nothing more: it does not fetch, estimate, classify, or aggregate. Degenerate inputs (NaN radius, infinite time, all-null optionals) pass straight through to the advisor, which is itself total and degrades conservatively.

Advisory-only. This package labels the moment; she drives it. It never says "safe" and never tells her to turn back — that is the advisor's contract, and this seam does not widen it.