Replace 200ms polling with an event listener once highway emits a sections-changed event

[mogul]

Restored from slopsmith/slopsmith-plugin-sectionmap#6 — original issue, opened by @byrongamatos on 2026-05-09.
[restored-from: slopsmith/slopsmith-plugin-sectionmap#6]

From specs/001-section-map/tasks.md — generated retrospectively by spec-kit.

Replace 200ms polling with an event listener once highway emits a sections-changed event.

---

See specs/001-section-map/spec.md and specs/001-section-map/analyze.md for context.
This issue was filed in bulk; close as wontfix if no longer relevant.

[carochacs]

Investigated: highway (core) has no dedicated sections-changed event — sections arrive over the WS with no signal of their own. It does emit song:ready once section/phrase data has fully landed, so get-flashbacks#3 wires that up to build the bar immediately instead of waiting on the poller.

The setInterval(_smUpdate, 200) itself has to stay, though: the position marker, active-section highlight, and glass-fill all need continuous updates tied to the live audio clock every tick, and there's no event that fires per-frame without just being polling under another name. So this is addressed as far as it can be without a Host change; the 200ms tick is now doing less (event-driven bar creation, no data-arrival latency) but can't be eliminated entirely.

PR: get-flashbacks#3