fix(host-sensors): never wait on a cold sampler, back off failing readers, one stats request at a time

docs/architecture-invariants.md

@@ -1029,7 +1029,7 @@ With `classic` nothing is left behind: no headings, no breaks, no inline order,
 
 ### Header stats styles
 
-**Header stats styles** (`headerStatsStyle`, per-device, desktop only, default `compact`; Discussion #426 option G): how the WS readout, CPU, MEM and the plan-usage windows are drawn. `tiles` gives each its own label-over-value tile with a bar along the bottom edge; `compact` is two pills, WS / CPU / MEM and the plan windows, with a ring beside every value (stat rings accent, red past 80%; plan rings green, yellow or red); `classic` is the bars and `5H · 7D` chip as before. `data-header-stats` on `<html>` (pre-paint, then `applyHeaderStatsStyle()` from `applyHeaderVisibilitySettings()`) drives every rule; narrower than 768px and in a solo window it resolves to `classic`, because the stats are hidden there anyway and the moves below would otherwise reach the phone header.
+**Header stats styles** (`headerStatsStyle`, per-device, desktop only, default `compact`; Discussion #426 option G): how the WS readout, CPU, MEM and the plan-usage windows are drawn. `tiles` gives each its own label-over-value tile with a bar along the bottom edge; `compact` is two pills, WS / CPU / MEM and the plan windows, with a ring beside every value (stat rings accent, red past 80%; plan rings green, yellow or red); `classic` is the bars and `5H · 7D` chip as before. `data-header-stats` on `<html>` (pre-paint, then `applyHeaderStatsStyle()` from `applyHeaderVisibilitySettings()`) drives every rule; narrower than 768px and in a solo window it resolves to `classic`, because the stats are hidden there anyway and the moves below would otherwise reach the phone header. The opt-in host readings after MEM (GPU, VRAM, GPU MHz, CPU MHz: `.stat-item` elements that start `hidden` and are shown by `_updateHostSensors` in panels-ui.js) rely on `html[data-header-stats] .header-system-stats .stat-item[hidden]` in styles.css outranking the Tiles style's own `display` on `.stat-item`; keep that selector's specificity above any style rule that sets `display` on a stat item, or the hidden placeholders (`--%`) reappear.
 
 ⚠️ The clustered styles need the three elements contiguous, and the template keeps the classic order, so `applyHeaderStatsStyle()` MOVES `#connectionIndicator` into `#headerSystemStats` (first child) and `#planUsageChip` right after it, and `classic` moves them back to comment anchors it left at the template positions. Ids are unchanged, so every writer still finds them. ⚠️ The indicator joins the pill only while System Stats is shown: the pill is hidden with `display: none`, and the WS readout must not disappear with it.