Streaming ingest pipeline: push records into an ephemeral buffer slot, then aggregate the buffer in the same handler

stream_ingest.cell

// Streaming ingest pipeline: push records into an ephemeral buffer slot, then
// aggregate the buffer in the same handler. Demonstrates a List slot, slot.push,
// reading the buffer back with slot.all, and piping it through agg + sort_by.

cell StreamIngest {
    face {
        signal process(batch: List) -> Map
    }

    memory {
        buffer: List<String> [ephemeral]
    }

    // Ingest a batch of sensor readings, then summarize per device.
    on process(batch: List) {
        for r in batch { buffer.push(r) }
        let rows = buffer.all
        return map("ingested", len(rows), "summary", summarize(rows))
    }

    // Pure aggregation step — no memory, so it is deterministic to test.
    on summarize(rows: List) {
        return rows
            |> agg("device", "reading:sum", "reading:avg", "reading:count")
            |> sort_by("reading_sum", "desc")
    }

    on sample() {
        return list(
            map("device", "s1", "reading", 10),
            map("device", "s2", "reading", 5),
            map("device", "s1", "reading", 20),
            map("device", "s2", "reading", 15),
            map("device", "s1", "reading", 30)
        )
    }

    on run() {
        let result = process(sample())
        for r in result.summary { print("{r.device}: sum {r.reading_sum}, avg {r.reading_avg}") }
        return result.ingested
    }
}

cell test StreamIngestTests {
    rules {
        // pure summarize over the sample batch is deterministic
        // s1 = 10 + 20 + 30 = 60, s2 = 5 + 15 = 20 -> s1 leads
        assert summarize(sample())[0].device == "s1"
        assert summarize(sample())[0].reading_sum == 60
        assert (summarize(sample()) |> filter_by("device", "=", "s2"))[0].reading_sum == 20
        assert summarize(sample())[0].reading_count == 3
    }
}