feat(telemetry): implement app-extended-heartbeat event

[khanayan123]

Summary

Implement the `app-extended-heartbeat` telemetry event for the Ruby tracer.

Motivation

Long-running services (24h+) currently only report their configuration state via the initial `app-started` event. If the backend misses or loses that event, there's no way to recover visibility into the SDK's configuration. The `app-extended-heartbeat` event solves this by re-sending the full configuration payload every 24h, ensuring reliable state reporting for long-running instances.

Implementation

`AppExtendedHeartbeat` inherits `AppStarted` to reuse its configuration-building logic. Rather than snapshotting configuration at startup, the worker recomputes the full payload fresh at each firing by passing `settings` and `agent_settings` directly — this means remote config changes are correctly reflected in the periodic heartbeat.

The interval is configurable via `DD_TELEMETRY_EXTENDED_HEARTBEAT_INTERVAL` (in seconds) for system test parity validation; the default (86400s) is defined solely in the config DSL. The tick-counter approach mirrors the existing heartbeat pattern and resets correctly after fork via `initialize_state`.

Change log entry

Yes. Add `app-extended-heartbeat` telemetry event emitted every 24h with full configuration payload (including remote config changes) for long-running service visibility.

Related

• System test PR: Add end-to-end test for app-extended-heartbeat telemetry event system-tests#6338

[github-actions]

Thank you for updating Change log entry section 👏

^{Visited at: 2026-04-01 14:13:45 UTC}

[github-actions]

Typing analysis

Note: Ignored files are excluded from the next sections.

steep:ignore comments

This PR introduces 1 steep:ignore comment, and clears 1 steep:ignore comment.

steep:ignore comments (+1-1)

❌ Introduced:

lib/datadog/core/telemetry/worker.rb:289

✅ Cleared:

lib/datadog/core/telemetry/worker.rb:269

Untyped methods

This PR introduces 1 untyped method and 2 partially typed methods, and clears 1 untyped method. It decreases the percentage of typed methods from 61.69% to 61.68% (-0.01%).

Untyped methods (+1-1)

❌ Introduced:

sig/datadog/core/telemetry/worker.rbs:67
└── def buffer_klass: () -> untyped

✅ Cleared:

sig/datadog/core/telemetry/worker.rbs:61
└── def buffer_klass: () -> untyped

Partially typed methods (+2-0)

❌ Introduced:

sig/datadog/core/telemetry/event/app_extended_heartbeat.rbs:8
└── def initialize: (settings: untyped, agent_settings: Core::Configuration::AgentSettings) -> void
sig/datadog/core/telemetry/worker.rbs:32
└── def initialize: (?enabled: bool, heartbeat_interval_seconds: Float, extended_heartbeat_interval_seconds: Integer, metrics_aggregation_interval_seconds: Float, emitter: Emitter, metrics_manager: MetricsManager, settings: untyped, agent_settings: Core::Configuration::AgentSettings, ?shutdown_timeout: Float | Integer, ?buffer_size: Integer, dependency_collection: bool, logger: ::Logger) -> void

Untyped other declarations

This PR introduces 1 untyped other declaration. It increases the percentage of typed other declarations from 77.73% to 77.75% (+0.02%).

Untyped other declarations (+1-0)

❌ Introduced:

sig/datadog/core/telemetry/worker.rbs:25
└── @settings: untyped

If you believe a method or an attribute is rightfully untyped or partially typed, you can add # untyped:accept on the line before the definition to remove it from the stats.

[datadog-prod-us1-5]

✅ Tests

🎉 All green!

❄️ No new flaky tests detected
🧪 All tests passed

🎯 Code Coverage (details)
• Patch Coverage: 93.40%
• Overall Coverage: 95.36% (+0.00%)

_{This comment will be updated automatically if new data arrives.
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[p-datadog]

Clean implementation — the tick-counter approach mirrors the existing heartbeat pattern nicely, and the initialize_state placement of @extended_heartbeat_ticks correctly resets the 24h timer after fork.

A couple of things caught my eye below.

[vpellan]

Requesting change to include configs changed through remote config.

[p-datadog]

👍 LGTM

[khanayan123]

/merge

[gh-worker-devflow-routing-ef8351]

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2026-04-01 18:26:34 UTC ℹ️ Start processing command /merge

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2026-04-01 18:35:21 UTC ℹ️ MergeQueue: merge request added to the queue

The expected merge time in master is approximately 35m (p90).

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2026-04-01 19:14:51 UTC ℹ️ MergeQueue: This merge request was merged