Crane load moment — the tipping write is refused by the ledger

crane_load_moment.cell

// CRANE LOAD MOMENT — the tipping write is refused by the ledger.
// "Big Blue", Miller Park, 1999: a 567-ton lift in wind put the crawler
// crane past its load moment and it came down across the stadium —
// 3 ironworkers dead. Load moment is load x radius against the rated
// chart; the killer is that each input looks fine alone. Here the
// computed moment percentage is written to a slot whose invariant tops
// out at 100: a lift plan that tips the crane is REJECTED AT THE WRITE,
// so the hoist edge is never taken. The machine adds the second wall —
// a crane cannot hoist from `parked`, and an out-of-chart plan leaves
// it safely in `rigged`.

cell LoadMomentIndicator {
    face {
        signal rig(id: String) -> String
        signal plan_lift(id: String, tons: Int, radius_m: Int, rated_tm: Int) -> Map
        signal set_down(id: String) -> String
        signal park(id: String) -> String
        signal moment_now(id: String) -> Int
    }

    memory {
        // percent of rated load moment — 100 is the chart edge, not a hint
        moment_pct: Map<String, Int> [persistent, consistent]
        invariant moment_pct >= 0 && moment_pct <= 100
    }

    state crane {
        initial: parked
        parked -> rigged           // counterweights on, outriggers set
        rigged -> parked
        rigged -> hoisting         // only a chart-checked load gets here
        hoisting -> rigged
    }

    on rig(id: String) { transition(id, "rigged")  return get_status(id) }

    on plan_lift(id: String, tons: Int, radius_m: Int, rated_tm: Int) {
        if rated_tm <= 0 { return map("ok", false, "reason", "no load chart") }
        let pct = idiv(tons * radius_m * 100, rated_tm)
        // THE wall: a moment past 100% cannot be written, so the
        // hoist below it is never reached.
        let w = try { moment_pct.set(id, pct) }
        if w.error != () {
            return map("ok", false, "state", get_status(id),
                       "reason", "load moment {pct}% of chart — lift refused")
        }
        let r = try { transition(id, "hoisting") }
        if r.error != () {
            return map("ok", false, "reason", "crane not rigged")
        }
        return map("ok", true, "state", get_status(id), "moment_pct", pct)
    }

    on set_down(id: String) {
        moment_pct.set(id, 0)
        transition(id, "rigged")
        return get_status(id)
    }

    on park(id: String) { transition(id, "parked")  return get_status(id) }
    on moment_now(id: String) { return moment_pct.get(id) ?? 0 }
}

cell test CraneTests {
    rules {
        // no hoisting from parked — the edge does not exist
        assert_fails transition("c1", "hoisting")

        // an in-chart lift proceeds: 400t at 20m on a 10000 t-m chart = 80%
        assert rig("c1") == "rigged"
        assert plan_lift("c1", 400, 20, 10000).ok == true
        assert moment_now("c1") == 80

        // come back down before the next plan
        assert set_down("c1") == "rigged"

        // THE Big Blue lift: 567t at 26m on the same chart = 147%.
        // The ledger refuses the write; the crane never leaves `rigged`.
        assert plan_lift("c1", 567, 26, 10000).ok == false
        assert moment_now("c1") == 0

        // the wall holds even against a direct write
        assert_fails moment_pct.set("c1", 147)
        assert_fails moment_pct.set("c1", -10)

        // a rigged crane that never lifted can stand down
        assert park("c1") == "parked"
    }
}