[chain-pr 7/10] DatadogFlags: typed-bus migration

[maxep]

This PR is part of a chain split from maxep/message-bus-subscription by chain-pr.

What and why?

With CoreMessageBus implementing the typed MessageBus protocol (PR #2929), DatadogFlags can stop routing flag evaluation events through FeatureScope and send them directly on the typed bus.

RUMFlagEvaluationReporter previously held a FeatureScope reference and called featureScope.send(message: .payload(RUMFlagEvaluationMessage(...))). The FeatureScope was only used for its send capability, not for event writing, making it a heavier dependency than needed. It now holds a MessageBus reference and calls messageBus.send(message:) directly.

This simplifies the FlagsFeature factory: makeRUMFlagEvaluationReporter previously required a FeatureScope argument passed through from FlagsClient. That argument is removed — the factory closure now captures core.messageBus directly at feature initialisation time.

How?

RUMFlagEvaluationReporter.swift — FeatureScope → MessageBus

// Before
private let featureScope: any FeatureScope
init(featureScope: any FeatureScope) { ... }

func sendFlagEvaluation<T>(flagKey: String, value: T) where T: FlagValue {
    featureScope.send(message: .payload(RUMFlagEvaluationMessage(flagKey: flagKey, value: value)))
}

// After
private let messageBus: any MessageBus
init(messageBus: any MessageBus) { ... }

func sendFlagEvaluation<T>(flagKey: String, value: T) where T: FlagValue {
    messageBus.send(message: RUMFlagEvaluationMessage(flagKey: flagKey, value: value))
}

FlagsFeature.swift — factory closure captures messageBus

// Before
let makeRUMFlagEvaluationReporter: (any FeatureScope) -> any RUMFlagEvaluationReporting

makeRUMFlagEvaluationReporter = { featureScope in
    return RUMFlagEvaluationReporter(featureScope: featureScope)
}

// After
let makeRUMFlagEvaluationReporter: () -> any RUMFlagEvaluationReporting

makeRUMFlagEvaluationReporter = { [messageBus = core.messageBus] in
    return RUMFlagEvaluationReporter(messageBus: messageBus)
}

FlagsClient.swift — call site simplification

// Before
rumFlagEvaluationReporter: feature.makeRUMFlagEvaluationReporter(featureScope)

// After
rumFlagEvaluationReporter: feature.makeRUMFlagEvaluationReporter()

Review checklist

• Feature or bugfix MUST have appropriate tests (unit, integration)
• Make sure each commit and the PR mention the Issue number or JIRA reference
• Add CHANGELOG entry for user facing changes
• Add Objective-C interface for public APIs - see our guidelines (internal)
• Run make api-surface when adding new APIs

---

Chain overview

#	PR	Title
1	#2927	Typed MessageBus protocol and shared message types
2	#2928	Test infrastructure for typed message bus
3	#2929	DatadogCore: CoreMessageBus implementation and rename
4	#2930	DatadogCrashReporting: typed-bus migration
5	#2931	DatadogLogs: typed-bus migration
6	#2932	DatadogTrace: typed-bus migration
7	← this PR	DatadogFlags: typed-bus migration
8	#2934	DatadogRUM: typed-bus migration and TelemetryInterceptor merge
9	#2935	DatadogSessionReplay and DatadogWebViewTracking: typed-bus migration
10	#2936	Documentation updates

graph LR
    G1["1 — Typed MessageBus protocol and shared message types"]
    G2["2 — Test infrastructure for typed message bus"]
    G3["3 — DatadogCore: CoreMessageBus implementation and rename"]
    G4["4 — DatadogCrashReporting: typed-bus migration"]
    G5["5 — DatadogLogs: typed-bus migration"]
    G6["6 — DatadogTrace: typed-bus migration"]
    G7["7 — DatadogFlags: typed-bus migration"]
    G8["8 — DatadogRUM: typed-bus migration and TelemetryInterceptor merge"]
    G9["9 — DatadogSessionReplay and DatadogWebViewTracking: typed-bus migration"]
    G10["10 — Documentation updates"]
    G1 --> G2
    G2 --> G3
    G3 --> G4
    G3 --> G5
    G5 --> G6
    G3 --> G7
    G6 --> G8
    G7 --> G8
    G8 --> G9
    G1 --> G10

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Merge in dependency order. PRs with no incoming edges from un-merged PRs can be reviewed in parallel.

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Avoid leaking flag receivers across RUM registrations

When RUM is enabled more than once on the same core, or when RUMFeature is constructed but core.register(feature:) later fails, this installs a new typed-bus FlagEvaluationReceiver that is never replaced or unsubscribed; the typed bus retains receivers until unsubscribe, unlike the legacy messageReceiver path that DatadogCore.register replaces by feature key. Later flag evaluations are therefore delivered to stale monitors as well as the current one, which can duplicate feature-flag updates or use stale RUM configuration. Store the receiver/subscription and remove or replace it during teardown/re-registration.

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