hive-metric: delta counters by default, cumulative opt-in

A stateless one-shot CLI can't track a running total across invocations,
so cumulative-by-default semantics required a caller to already know and
report the accumulated value every time -- awkward for the common case
(an agent incrementing a counter by 1 per event). Delta is now the
default: send the contribution since the last report, and the collector
accumulates. --temporality cumulative is available for the rare caller
that already tracks its own running total. gauge behavior unchanged.

hive-metric/src/main.rs

@@ -12,7 +12,7 @@
 //!
 //! # Usage
 //! ```text
-//! hive-metric <name> <value> [--type counter|gauge] [--labels key=value...]
+//! hive-metric <name> <value> [--type counter|gauge] [--temporality delta|cumulative] [--labels key=value...]
 //! ```
 
 use anyhow::{Context, Result, bail};
@@ -20,6 +20,7 @@ use clap::Parser;
 use opentelemetry::KeyValue;
 use opentelemetry::metrics::MeterProvider;
 use opentelemetry_otlp::{Protocol, WithExportConfig};
+use opentelemetry_sdk::metrics::Temporality;
 
 #[derive(Parser)]
 #[command(
@@ -39,10 +40,17 @@ struct Cli {
     /// negative; counters must be >= 0 (they only increase).
     value: f64,
 
-    /// Metric kind: `counter` (cumulative sum, default) or `gauge` (instantaneous value).
+    /// Metric kind: `counter` (increasing sum, default) or `gauge` (instantaneous value).
     #[arg(long = "type", value_name = "TYPE", default_value = "counter")]
     metric_type: MetricKind,
 
+    /// Counter reporting mode: `delta` (this call's own contribution, default —
+    /// send `1` each time and the collector accumulates) or `cumulative` (this
+    /// call reports the running total, which a stateless one-shot CLI can't
+    /// track itself — only meaningful for `--type counter`; ignored for `gauge`).
+    #[arg(long, value_name = "MODE", default_value = "delta")]
+    temporality: TemporalityArg,
+
     /// Extra label(s) as `key=value` pairs. May be repeated.
     /// Resource labels (agent, hive, swarm) come from `OTEL_RESOURCE_ATTRIBUTES`
     /// automatically — do not re-specify them here.
@@ -52,12 +60,29 @@ struct Cli {
 
 #[derive(Clone, Debug, clap::ValueEnum)]
 enum MetricKind {
-    /// Counter: monotonically increasing cumulative sum (default).
+    /// Counter: increasing sum (default).
     Counter,
     /// Gauge: point-in-time instantaneous value.
     Gauge,
 }
 
+#[derive(Clone, Debug, clap::ValueEnum)]
+enum TemporalityArg {
+    /// Report this call's own contribution since the last report (default).
+    Delta,
+    /// Report the running total as of this call.
+    Cumulative,
+}
+
+impl From<TemporalityArg> for Temporality {
+    fn from(arg: TemporalityArg) -> Self {
+        match arg {
+            TemporalityArg::Delta => Temporality::Delta,
+            TemporalityArg::Cumulative => Temporality::Cumulative,
+        }
+    }
+}
+
 fn main() -> Result<()> {
     let cli = Cli::parse();
 
@@ -86,6 +111,7 @@ fn main() -> Result<()> {
     let exporter = opentelemetry_otlp::MetricExporter::builder()
         .with_http()
         .with_protocol(Protocol::HttpJson)
+        .with_temporality(cli.temporality.into())
         .build()
         .context("failed to build OTLP metric exporter")?;