feat!: DISABLED is a successful evaluation (still defaults)

[jonathannorris]

• Disabled flags now resolve successfully with reason=DISABLED instead of errorCode=FLAG_NOT_FOUND. See the ADR.
• Breaking, but barely: resolved values are unchanged (the caller-provided default is still surfaced).
• The break is only observable for consumers that inspect reason / errorCode on disabled-flag evaluations.

Related Issues

Closes #1799
Part of open-feature/flagd#1965

[gemini-code-assist]

Code Review

This pull request updates the behavior of disabled feature flags to return a disabled reason instead of an error code. However, the current implementation returns a null value for disabled flags, which can lead to NullPointerExceptions in client applications. The reviewer suggests returning the user-provided default value instead of null when a flag is disabled, and updating the corresponding unit tests to assert this behavior.

[Copilot]

Pull request overview

This PR updates the in-process flagd-core evaluation behavior to treat state: DISABLED as a successful evaluation with reason=DISABLED (instead of returning FLAG_NOT_FOUND), and ensures disabled evaluations include flag metadata.

Changes:

• FlagdCore: return reason=DISABLED for disabled flags (no errorCode/errorMessage) and include flag metadata.
• MockEvaluator: align test evaluator behavior with the new disabled-flag semantics.
• Tests: update assertions in flagd-core and providers/flagd to expect reason=DISABLED with no value/variant.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 4 comments.

File	Description
tools/flagd-core/src/main/java/dev/openfeature/contrib/tools/flagd/core/FlagdCore.java	Changes disabled-flag evaluation to return reason=DISABLED and include metadata.
tools/flagd-core/src/test/java/dev/openfeature/contrib/tools/flagd/core/FlagdCoreTest.java	Updates disabled-flag test expectations for FlagdCore.
providers/flagd/src/test/java/dev/openfeature/contrib/providers/flagd/resolver/process/MockEvaluator.java	Updates mock evaluator disabled-flag behavior used by in-process resolver tests.
providers/flagd/src/test/java/dev/openfeature/contrib/providers/flagd/resolver/process/InProcessResolverTest.java	Updates disabled-flag assertions for in-process resolver tests.

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[toddbaert]

Marking as draft for now - we need the flagd and testbed update first.