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## This PR

Adds OpenTelemetry metrics for the gRPC flag sync service to enable
monitoring of sync connections and operations.

  ### Metrics

  **Custom Metrics:**
  | Metric | Type | Description |
  | ------ | ---- | ----------- |
| `feature_flag.flagd.sync.active_streams` | Gauge | Currently active
streaming connections |
| `feature_flag.flagd.sync.stream.duration` | Histogram | Duration of
streaming connections (seconds) |

  **Standard gRPC Metrics:**
- Leverages `otelgrpc.NewServerHandler()` for comprehensive gRPC server
metrics (request counts, latencies, status codes, etc.)

  ### Changes

- Add custom sync metric definitions in `core/pkg/telemetry/metrics.go`
  - Instrument `SyncFlags` streaming RPC with stream lifecycle metrics
  - Enable standard gRPC metrics via OpenTelemetry gRPC instrumentation
- Add unit tests for metric collection, histogram buckets, and
NoopMetricsRecorder

---------

Signed-off-by: Alexandre Chakroun <[email protected]>

🤖 I have created a release *beep* *boop*
---


<details><summary>flagd: 0.14.5</summary>

##
[0.14.5](flagd/v0.14.4...flagd/v0.14.5)
(2026-03-27)


### ✨ New Features

* gRPC sync endpoint metrics
([#1861](#1861))
([b04dc50](b04dc50))
</details>

<details><summary>core: 0.14.3</summary>

##
[0.14.3](core/v0.14.2...core/v0.14.3)
(2026-03-27)


### ✨ New Features

* gRPC sync endpoint metrics
([#1861](#1861))
([b04dc50](b04dc50))
</details>

---
This PR was generated with [Release
Please](https://github.com/googleapis/release-please). See
[documentation](https://github.com/googleapis/release-please#release-please).

Signed-off-by: OpenFeature Bot <[email protected]>
Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>