Interface SpectrumMessage

A real-time-analyzer frame for the STANDALONE panel (the /rta rows over ?watch=1): raw linear-magnitude FFT bins for one channel (any lane the desk is analysing — see /channel/{kind}/{index}/rta). mags[k] is the amplitude at k · sampleRate / fftSize Hz. This is the web-ui's SpectrumFrame shape verbatim — the browser's aggregateBands does the log-band/dB reduction, so the server sends the raw FFT once and the client decides how to slice it (bar count, tilt, freeze) with no server round-trip.

low is an OPTIONAL second tier (issue #95, "zoom-FFT"): the same tap's spectrum again, decimated ÷8 before its own FFT — ~8× finer Hz/bin, covering the low end where a single fixed-size FFT is too coarse on a log display. post is an OPTIONAL second TAP (issue #96): a watched strip's POST-EQ spectrum (with its own high + low tiers), the top-level fields being the PRE-EQ tap — the client draws pre / post / both. Both optionals are additive: an older server build (single-tap, single-tier) still parses on either end; the client falls back to HIGH-tier-only / PRE-only when they're absent.