load_m1_window cannot express an open upper bound: it hardcodes
Some(from_ms)/Some(to_ms) into stream_m1_windowed, so callers reach for
the i64::MAX sentinel, which panics upstream in chrono's
from_timestamp_millis (data-server records.rs:28). This compile-RED pins
the desired Option<i64> contract (None = unbounded) and asserts an
unbounded read equals the finite sane bound bar-for-bar.
refs #23
