Stamp build_info and mark reserved-always-zero series as reserved

README.md

@@ -207,12 +207,12 @@ won't be renamed.
 | `epmon_service_up` | gauge | Alerting: `epmon_service_up == 0` pages. State, not last probe. |
 | `epmon_probe_total{result="success"\|"failure"}` | counter | Raw outcome rates; burn-rate alerts. |
 | `epmon_probe_duration_seconds` | histogram | Latency: `histogram_quantile(0.99, sum(rate(epmon_probe_duration_seconds_bucket[5m])) by (service, le))` for p99 degradation and slow drift. Buckets: 5ms…10s. |
-| `epmon_probe_skipped_total` | counter | Overlap-guard skips (scheduler shed load). |
-| `epmon_store_queue_depth`, `epmon_store_cmd_queue_depth` | gauges | Internal backpressure; sustained non-zero deserves a look. |
-| `epmon_store_dropped_total`, `epmon_store_write_timeout_total` | counters | Lost or aborted writes — alert on increase. |
-| `epmon_service_history_migrated_total{result="ok"\|"no_match"}` | counter | Alias-migration outcomes after reloads. |
-| `epmon_config_reload_total{result="ok"\|"error"}` | counter | Config reload outcomes. |
-| `epmon_uptime_seconds`, `epmon_build_info` | gauge | Process age and build identity. |
+| `epmon_probe_skipped_total` | counter | Reserved: overlap-guard skips (no guard exists yet; always zero). |
+| `epmon_store_queue_depth`, `epmon_store_cmd_queue_depth` | gauges | Reserved: internal backpressure hooks for a future store actor; always zero. |
+| `epmon_store_dropped_total`, `epmon_store_write_timeout_total` | counters | Reserved: unwritable today, so permanently zero — do not alert on them. |
+| `epmon_service_history_migrated_total{result="ok"\|"no_match"}` | counter | Reserved: alias-migration outcomes (no migration path exists yet). |
+| `epmon_config_reload_total{result="ok"\|"error"}` | counter | Reserved: config reload outcomes (no reload path exists yet). |
+| `epmon_uptime_seconds`, `epmon_build_info` | gauge | Process age and build identity (`version`/`commit` from release ldflags). |
 
 ## Development
 

cmd/epmon/main.go

@@ -109,6 +109,7 @@ func runDefault(args []string, stdout, stderr io.Writer) int {
 	}
 
 	registry := metrics.New()
+	registry.SetBuildInfo(version, commit)
 	sched := scheduler.New(cfg, st, registry)
 	sched.Run(ctx)
 	defer sched.Stop()

internal/metrics/metrics_test.go

@@ -72,6 +72,19 @@ func TestHistogramBoundedState(t *testing.T) {
 	}
 }
 
+// TestBuildInfo pins the stamped build identity line. The binary wires
+// its ldflags version/commit into the registry at boot (see runDefault);
+// an empty rendering means that wiring regressed.
+func TestBuildInfo(t *testing.T) {
+	r := New()
+	r.SetBuildInfo("v1.2.3", "abc1234")
+	out := r.Snapshot()
+	want := `epmon_build_info{version="v1.2.3",commit="abc1234"} 1`
+	if !strings.Contains(out, want) {
+		t.Errorf("snapshot missing %q\n%s", want, out)
+	}
+}
+
 func TestHandler(t *testing.T) {
 	r := New()
 	h := r.Handler()