classDiagram
    direction TB
    class RealtimeObservationSource {
        <<port>>
        +collect(Request request) CollectionAttempt
    }
    class CollectionAttempt {
        -String attemptId
        -String sourceOperation
        -Instant requestedAt
        -String callPolicyRef
        -String retentionPolicyVersion
    }
    class CollectionOutcome {
        <<sealed state>>
        -String kind
        -Instant receivedAt
        -String contentDigest
    }
    class RetentionPolicy {
        -String policyId
        -String version
        +decision(String dataset, String field) Decision
    }
    class ObservationNormalizer {
        +normalize(CollectionAttempt attempt) ObservationBatch
    }
    class ObservationBatch {
        -String batchId
        -String attemptId
        -Instant availableAt
    }
    class BusObservation {
        -String observationId
        -String routeAxisRef
        -Instant sourceObservedAt
        -Instant receivedAt
        -Instant availableAt
    }
    class SeatReading {
        -String state
        -Integer remainingSeats
        -String reason
    }
    class BusPosition {
        -int lastPassedSequence
        -String phase
    }
    class PrivateVehicleRef {
        -String tokenVersion
        -String token
    }
    class PassageDeriver {
        +derive(List~ObservationBatch~ window) Result
    }
    class TripSegment {
        -String segmentId
        -String journeyKey
        -LocalDate serviceDateKst
        -Instant startedAt
        -Instant endedAt
    }
    class PassageEvidence {
        -String evidenceId
        -String kind
        -List~Integer~ candidateStopSequences
        -int elapsedSeconds
        -String terminalPhase
        -String derivationVersion
    }
    class EvidenceRef {
        -String role
        -String observationBatchId
        -String observationId
    }

    RealtimeObservationSource --> CollectionAttempt
    CollectionAttempt *-- CollectionOutcome
    CollectionAttempt --> RetentionPolicy
    ObservationNormalizer ..> CollectionAttempt
    ObservationNormalizer ..> RetentionPolicy
    ObservationNormalizer --> ObservationBatch
    ObservationBatch --> CollectionAttempt
    ObservationBatch *-- BusObservation
    BusObservation *-- SeatReading
    BusObservation *-- BusPosition
    BusObservation --> PrivateVehicleRef
    PassageDeriver ..> ObservationBatch
    PassageDeriver --> TripSegment
    PassageDeriver --> PassageEvidence
    TripSegment "1" <-- "0..*" PassageEvidence
    PassageEvidence *-- "2" EvidenceRef
    EvidenceRef ..> BusObservation
    PassageEvidence --> SeatReading