Toccata Cleanup - Part 2

[biryukovmaxim]

Stack

1. Toccata Cleanup - Part 1 #1082 Part 1 - transition-only machinery (base: master)
2. Toccata Cleanup - Part 2 #1083 Part 2 - consensus activation checks
3. Toccata Cleanup - Part 3 #1084 Part 3 - txscript covenants flag
4. Toccata Cleanup - Part 4 #1086 Part 4 - mining and mempool policy

Each PR targets the branch below it, so its diff contains only its own layer. Review bottom to top.

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Second of a stacked series removing dead Toccata activation handling. Stacked on #1082; review that one first, this PR's diff is only the changes on top of it.

Toccata activated on mainnet at DAA 474_165_565 and testnet at 467_579_632. With a 30 hour pruning duration and a 432,000 block finality depth, pruning_point.daa_score - finality_depth > toccata_activation holds on every live network. That is what makes the pre-Toccata branches below unreachable, including the ones that operate inside the [pruning_point - finality_depth, pruning_point] window. Part 1 activated Toccata on devnet, so all networks are now post-activation.

This part collapses every activation check inside the consensus crates to its post-Toccata branch, and drops each toccata_activation field once its last reader is gone. Params::toccata_activation deliberately stays; it is still read outside consensus and is removed at the top of the stack.

Collapsed checks

• Transaction validator: the contextual check_transaction_version and check_transaction_signature_scripts_in_header_context are deleted, and the isolation-stage checks become the single enforcement point. This is what the deleted TODO(post-toccata) asked for, and it restores the arrangement described by validate_tx_in_isolation's own doc comment: checks live in header context only while they are activation dependent. check_covenant_info and the script engine's covenant flag become unconditional.
• Coinbase: the coinbase transaction is always built at TX_VERSION_TOCCATA.
• Header processor: check_header_version_in_context is deleted and the context-free check_header_version is restored in pre-GHOSTDAG validation. Historical headers are unaffected: pruning-proof headers are inserted directly by apply_proof without passing isolation validation, and ordinary IBD headers start at the current post-activation pruning point.
• Virtual processor: accepted_id_digests is always the single-element seq_commit form, chain qualification is unconditional, the seq commit accessor is always present, and the inactivity shortcut no longer folds to ZERO_HASH for pre-Toccata ancestors. calc_accepted_id_merkle_root is deleted once both callers are gone.
• Pruning: SMT store pruning is unconditional, and the pruning-proof chain segment is always built on both the syncer and syncee sides, without the inner breaks that stopped below the activation.
• Body processor and get_seq_commit_lane_proof lose their remaining gates.

ForkedParam call sites move from .get(daa_score) to .after() rather than to plain constants. The field types stay as they are and collapse to plain values at the top of the stack, so this PR contains no parameter-shape changes.

Genesis accepted-id digests

compute_genesis_accepted_id_digests branched on the genesis DAA score. Mainnet and testnet genesis predate the activation, so the pre-Toccata branch was the live one for them, but it is collapsed here along with the rest.

A node with an existing database does not process genesis at all. A node starting from an empty database does compute this value, but discards it while syncing, because the headers proof builds a staging consensus that skips genesis and seeds virtual state at the current pruning point. Any network defined from now on is post-activation at genesis. The reasoning is recorded in a doc comment on the function.

This is also what allows Params::toccata_activation to be deleted entirely later in the series, rather than kept for a computation that permanently depends on the activation score.

Removed plumbing

toccata_activation is dropped from TransactionValidator, CoinbaseManager, PruningProofManager, VirtualStateProcessor and SeqCommitAccessor, together with their constructor arguments and services.rs call sites. UtxoProcessingContext::accepted_tx_ids and accepted_tx_versions are removed as well: the collapse left them written on every accepted transaction and read nowhere.

Test data

What changes in test data, how and why. Exactly one fixture changes, goref_custom_pruning_depth/blocks.json.gz, regenerated by rerunning simpa/generate-json-tests-data.sh rather than edited by hand. Its OverrideParams header line is identical to the previous one except toccata_activation: 1000 -> 0; pruning_depth: 450, finality_depth: 200 and every other param are unchanged, so the fixture still exercises the custom pruning depth it exists for. goref_custom_pruning_depth_test is not touched and still passes.

simpa's --test-pruning profile pinned toccata_activation at DAA 1000, so goref_custom_pruning_depth was a DAG spanning the activation with mixed header versions. Now that the header version check is unconditional, such a DAG is not valid input, so the toggle is removed and the fixture regenerated; it pins toccata_activation: 0 and is uniformly version 2. The file is a gzipped block dump, so it is meant to be reproduced with simpa/generate-json-tests-data.sh rather than read as a diff.

Integration tests covering the pre-activation to post-activation transition are deleted, since the transition no longer exists in the code. The durable invariants they shared coverage with (covenants, push limits, native payloads, KIP-10, header and transaction version enforcement) remain covered. One assertion in header_in_isolation_validation_test moves from BLOCK_VERSION to TOCCATA_BLOCK_VERSION, following the version check into isolation.

Not in scope

Params::toccata_activation, the ForkedParam getters, BLOCK_VERSION := 2 and TOCCATA_BLOCK_VERSION are handled at the top of the stack. The txscript EngineFlags covenant flag, the MiningManager/Mempool plumbing and protocol/flows follow in later parts. Pre-Toccata storage decoders (utxo/pre_toccata.rs, the EOF tolerant UtxoEntry deserializer, db_compat.rs) are permanent DB compatibility and are never removed, as are the TX_VERSION_TOCCATA keyed transaction rules.

A TODO is left on VirtualState::accepted_id_digests: it now always holds exactly one hash, and could become a dedicated type that serializes as a one-element vector, keeping the stored bytes identical while making the invariant explicit.