feat(inkless:config): enforce diskless feature flag dependency chain

[jeqo]

Add startup validation that enforces the dependency chain between diskless feature flags:

  diskless.storage.system.enable          ← base layer, can be enabled alone
    → diskless.managed.rf.enable          ← requires diskless.storage.system.enable
      → diskless.allow.from.classic.enable ← requires managed replicas + remote log storage

Brokers now fail fast with a clear error message if flags are enabled without their prerequisites.

Rationale for requiring diskless.managed.rf.enable:

1. Read-path after migration: consuming data that was tiered via classic remote storage needs the local UnifiedLog. Without managed replicas, that read path just returns INVALID_REQUEST — you can't read the full topic history.
2. Migration path: InitDisklessLog needs the leader to have a local log. With legacy RF=1 and hash-based routing, there's no guarantee the broker handling the request is actually the leader with a local log. Managed replicas give you stable, deterministic leadership.

[Copilot]

Pull request overview

Adds broker startup validation in KafkaConfig to enforce a dependency chain between diskless feature flags so misconfigured brokers fail fast instead of starting with an invalid combination of settings.

Changes:

• Add KafkaConfig.validateValues() checks enforcing diskless.storage.system.enable → diskless.managed.rf.enable → diskless.allow.from.classic.enable plus remote.log.storage.system.enable.
• Extend InklessConfigsTest cluster init helpers to set the new diskless.managed.rf.enable broker config.
• Add new tests intended to cover invalid flag combinations.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
core/src/main/scala/kafka/server/KafkaConfig.scala	Adds startup validation (require) enforcing the diskless feature-flag dependency chain.
core/src/test/java/kafka/server/InklessConfigsTest.java	Updates test cluster config wiring for managed replicas and adds dependency validation tests.

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[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

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[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.

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