fix: align voluntary exit pruning with inclusion rules

[solanaXpeter]

Motivation

OpPool currently prunes voluntary exits using older cross-fork rules even when the exit signature remains includable. That can drop valid exits from the pool before block production, including Deneb+ exits covered by EIP-7044 and builder voluntary exits after gloas.

Description

• reuse isVoluntaryExitSignatureIncludable() when pruning voluntary exits from OpPool
• keep pre-Deneb previous-fork exits and Deneb+ older-fork exits until they are no longer includable or finalized
• add focused unit coverage for pre-Deneb and Deneb+ pruning behavior

AI Assistance Disclosure

• External Contributors: I have read the contributor guidelines and disclosed my usage of AI below.

I consulted Codex to implement and validate the change.

[gemini-code-assist]

Code Review

This pull request refactors the voluntary exit pruning logic in OpPool by utilizing isVoluntaryExitSignatureIncludable and introduces unit tests to ensure correct behavior across various fork epochs. Feedback suggests extracting the fork sequence retrieval logic into a helper method to minimize code duplication.

[gemini-code-assist]

The logic to determine the fork sequence for a voluntary exit is repeated in multiple places (here and in getSlashingsAndExits). Extracting this into a private helper method would improve maintainability and ensure consistency across the pool's operations.

Suggested change

	const voluntaryExitFork = this.config.getForkSeq(computeStartSlotAtEpoch(voluntaryExit.message.epoch));
	const voluntaryExitFork = this.getVoluntaryExitFork(voluntaryExit);

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Drop pre-Capella exits when entering Deneb+

Pruning now defers entirely to isVoluntaryExitSignatureIncludable(), but that helper returns true for every exit once stateFork >= deneb, so pre-Capella signatures can survive indefinitely until finalized. This conflicts with the actual signature domain rule (getDomainForVoluntaryExit in packages/config/src/genesisConfig/index.ts fixes Deneb+ voluntary-exit verification to the Capella domain), meaning exits that were valid in Bellatrix/Capella gossip can become invalid at Deneb while still being kept and later selected for block production (which skips re-verifying exit signatures). On short-gap/custom fork schedules or during prolonged non-finality, this can lead to proposing blocks with invalid voluntary exits.

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