Lab chain of custody — a sample whose custody broke can never be reported, by construction A forensic toxicology or pathology result is only as trustworthy as the unbroken chain of custody behind it

chain_of_custody.cell

// ============================================================================
// LAB CHAIN OF CUSTODY — a sample whose custody broke can never be
// reported, by construction
// ============================================================================
//
// A forensic toxicology or pathology result is only as trustworthy as the
// unbroken chain of custody behind it. If a sample is left unsealed, or
// its identity can't be accounted for at any handoff, the result is
// inadmissible and clinically worthless — but the dangerous version is the
// lab that reports it anyway, and a treatment (or a conviction) rests on a
// possibly-swapped tube.
//
// Here a specimen walks collected → sealed → in_transit → received →
// analyzed → reported. The one terminal failure state is `compromised`:
// any custody break sends the sample there and it can NEVER reach
// `reported`. `soma verify` proves reported is unreachable from
// compromised, and that compromised is itself terminal — no "re-seal and
// pretend" path exists.
//
//   soma verify examples/corpus/medical/chain_of_custody.cell
//   soma test   examples/corpus/medical/chain_of_custody.cell
//   soma run    examples/corpus/medical/chain_of_custody.cell demo
// ============================================================================

cell ChainOfCustody {
    face {
        signal collect(sample: String) -> Map
        signal handoff(sample: String, step: String) -> Map
        signal breach(sample: String) -> Map
        signal report(sample: String) -> Map
        signal sample_state(sample: String) -> String
        signal demo() -> String
    }

    // `reportable` order: collected -> sealed -> in_transit -> received ->
    // analyzed -> reported. `compromised` is the TERMINAL trap: every
    // custody-bearing state can fall into it, none escape. verify proves
    // reported is unreachable once compromised.
    state specimen {
        initial: collected
        collected  -> sealed
        sealed     -> in_transit
        in_transit -> received
        received   -> analyzed
        analyzed   -> reported
        collected  -> compromised
        sealed     -> compromised
        in_transit -> compromised
        received   -> compromised
        analyzed   -> compromised
    }

    on collect(sample: String) {
        return map("ok", true, "state", get_status(sample))
    }

    // A legitimate handoff is the next step in the chain; the machine
    // rejects skipping a step (e.g. shipping an unsealed tube).
    on handoff(sample: String, step: String) {
        let r = try { transition(sample, step) }
        if r.error != () {
            return map("ok", false, "reason", "custody violation: {r.error}")
        }
        return map("ok", true, "state", get_status(sample))
    }

    on breach(sample: String) {
        let r = try { transition(sample, "compromised") }
        if r.error != () { return map("ok", false, "reason", "{r.error}") }
        return map("ok", true, "state", get_status(sample))
    }

    // Reporting is only reachable through an unbroken chain. A compromised
    // sample cannot transition to reported — the proof, not a policy memo.
    on report(sample: String) {
        let r = try { transition(sample, "reported") }
        if r.error != () {
            return map("ok", false, "reason", "cannot report: {r.error}")
        }
        return map("ok", true, "state", get_status(sample))
    }

    on sample_state(sample: String) {
        return get_status(sample)
    }

    on demo() {
        collect("tube-A")
        handoff("tube-A", "sealed")
        handoff("tube-A", "in_transit")
        breach("tube-A")                       // seal found broken at the dock
        let r = report("tube-A")               // REFUSED — chain is broken
        let st = sample_state("tube-A")
        print("after breach: report = {r}")
        print("final state:  {st}")
        return "demo done"
    }
}

cell test CustodyTests {
    rules {
        // an unbroken chain reaches reported
        assert collect("s1").ok == true
        assert handoff("s1", "sealed").ok == true
        assert handoff("s1", "in_transit").ok == true
        assert handoff("s1", "received").ok == true
        assert handoff("s1", "analyzed").ok == true
        assert report("s1").ok == true
        assert sample_state("s1") == "reported"

        // you cannot skip sealing — shipping a raw tube is rejected
        assert collect("s2").ok == true
        assert_fails transition("s2", "in_transit")

        // a breach is terminal and blocks reporting forever
        assert collect("s3").ok == true
        assert handoff("s3", "sealed").ok == true
        assert breach("s3").ok == true
        assert sample_state("s3") == "compromised"
        assert_fails transition("s3", "reported")
        assert_fails transition("s3", "sealed")
        assert report("s3").ok == false
    }
}