triedb: add namespace state merge path

[zander-xyz]

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[zander-xyz]

@claude review

[Copilot]

Pull request overview

This PR extends the Ethereum execution “state” plumbing to support namespaced state deltas in the BlockState merge/validation path (used by TrieDB namespace reads), and adds a regression test that exercises reads + merges across two namespaces.

Changes:

• Add State::get_namespace() accessor to expose the state’s optional namespace.
• Update BlockState::{can_merge,merge} to select the correct StateDeltas map (global vs per-namespace) when validating/merging.
• Extend the on-disk TrieDB test to cover namespaced merges and stale-state rejection.

Verdict: NEEDS CHANGES

Reviewed changes

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

File	Description
category/execution/ethereum/state3/state.hpp	Exposes the optional namespace from State for downstream merge logic.
category/execution/ethereum/state2/block_state.cpp	Routes merge/validation to namespace-specific deltas when State is namespaced.
category/execution/ethereum/db/test/test_db.cpp	Expands namespace test to validate merge behavior and stale-state rejection.

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[github-actions]

The changes cleanly extend BlockState::can_merge and BlockState::merge to route to the correct StateDeltas based on the State's namespace, mirroring the pattern already used in read_account / read_storage. The test covers namespace-scoped merges, cross-namespace isolation, and rejection of a stale state after an intervening merge.

A few very minor style/redundancy notes, none blocking:

• MONAD_ASSERT(state_) at the top of can_merge and the inner MONAD_ASSERT(deltas) in the loop are redundant now that the namespace branch already establishes deltas (and state_ is a construction-time invariant).
• merge uses NamespacedStateDeltas::accessor (write lock) but only needs a const_accessor since it mutates only the pointed-to StateDeltas, not the outer map.
• The raw deltas pointer outlives its accessor lock in both functions. This is safe today because ns_state_ has no erase code path, but worth keeping in mind if erasure is ever added.

Verdict: CORRECT

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