Sensors: one standard read interface — catalog, single value, history, shaped query

Every number the collector samples becomes a sensor with a stable dotted ID
(cpu.core.3.usage, fan.nct6775.fan2, fs.root.used_pct). Clients discover them
from the catalog and ask for exactly what they want, including as a shaped
query: send the object you want, get it back with the values filled in.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

internal/metrics/metrics.go

@@ -132,6 +132,8 @@ type Sample struct {
 	FS       []FS       `json:"fs"`
 	UPS      *UPS       `json:"ups"`
 	Uptime   float64    `json:"uptime"`
+
+	fsT, upsT int64 // when the slow sections were really read; sensors report these, not T
 }
 
 // Series is the compact history the UI seeds its sparklines from.
@@ -292,11 +294,11 @@ func (c *Collector) sample() {
 	if c.lastFS == nil || now.Sub(c.fsAt) >= fsEvery {
 		c.lastFS, c.fsAt = filesystems(), now
 	}
-	s.FS = c.lastFS
+	s.FS, s.fsT = c.lastFS, c.fsAt.UnixMilli()
 	if c.upsProbe != nil && (c.upsAt.IsZero() || now.Sub(c.upsAt) >= upsEvery) {
 		c.lastUPS, c.upsAt = c.upsProbe(), now
 	}
-	s.UPS = c.lastUPS
+	s.UPS, s.upsT = c.lastUPS, c.upsAt.UnixMilli()
 
 	if first {
 		return // deltas are meaningless on the priming pass