gRPC: Implement FetchBlock SyncService method via node kernel access

[carbolymer]

First UTxO RPC SyncService method: FetchBlock.

Clients can request blocks by slot and header hash. The response includes raw CBOR bytes and a structured cardano block header (slot, hash, height). Blocks are served directly from the node's ChainDB, avoiding N2C IPC overhead.

Error handling follows gRPC conventions:

• INVALID_ARGUMENT for malformed block references
• NOT_FOUND for blocks not present in ChainDB
• UNAVAILABLE while the node is still starting up

This PR implements part of:

• gRPC: Implement FetchBlock (UTxO RPC SyncService) in cardano-rpc #1216

Response completeness

The FetchBlock response populates nativeBytes and cardano.header fields. The following fields are not yet populated:

• Block.timestamp - Cardano blocks are slot-indexed, not timestamped. Computing wall-clock time from a slot requires era history from the ledger state, which is not yet accessible (blocked on the ledger snapshot migration).
• Block.body.tx - Returning structured transaction data requires deserialising raw CBOR and mapping to the UTxO RPC protobuf schema. This is a substantial standalone effort.

Clients needing full block data can deserialise nativeBytes themselves in the meantime.

Dependencies

• ADR-019: Node Kernel Access for cardano-rpc input-output-hk/cardano-node-wiki#94 must be approved before merging
• gRPC: fetchBlock method cardano-node#6579 - companion PR with cardano-node integration and E2E test

How to trust this PR

The E2E test lives in the companion cardano-node PR. To run:

1. Check out the metarepo with cardano-node branch mgalazyn/feature/fetchblock (PR #6579), which picks up cardano-api from this branch via the local cabal.project.
2. Run all RPC tests:

   TASTY_PATTERN='/RPC/' cabal test cardano-testnet-test
   

The FetchBlock test starts a testnet, queries the chain tip via CLI, fetches that block via gRPC, and verifies the response header matches the tip (slot, hash, block number). All 5 RPC tests pass - no regressions in existing methods.

Checklist

• Commit sequence broadly makes sense and commits have useful messages
• New tests are added if needed and existing tests are updated
• Self-reviewed the diff
• Changelog fragment added in .changes/

[Copilot]

Pull request overview

This PR adds initial UTxO RPC SyncService / FetchBlock support by introducing in-process node kernel access and using it to fetch blocks directly from the node’s ChainDB (returning raw CBOR bytes plus a structured Cardano header). It also extends Cardano.Api.Consensus re-exports to expose the consensus types needed for this integration.

Changes:

• Introduce NodeKernelAccessF and plumbing in the RPC server environment to access the node kernel once initialised, and add the FetchBlock gRPC handler.
• Add the UTxO RPC Sync protobuf definitions + generated bindings, and register the Sync service on the server.
• Re-export additional consensus/kernel/ChainDB types from Cardano.Api.Consensus to support node-kernel-based RPC implementations.

Reviewed changes

Copilot reviewed 17 out of 19 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
cardano-rpc/src/Cardano/Rpc/Server/NodeKernelAccess/Internal.hs	Implements node-kernel-backed nkaFetchBlock and environment lookup for kernel access (new module).
cardano-rpc/src/Cardano/Rpc/Server/NodeKernelAccess.hs	Defines NodeKernelAccessF and LedgerSnapshot callback record types (new module).
cardano-rpc/src/Cardano/Rpc/Server/Internal/UtxoRpc/Sync.hs	Implements the SyncService FetchBlock RPC method (new module).
cardano-rpc/src/Cardano/Rpc/Server/Internal/UtxoRpc/Query.hs	Renames blockNo binding to chainBlockNo for clarity in query methods.
cardano-rpc/src/Cardano/Rpc/Server/Internal/Tracing.hs	Adds SyncService tracing types (TraceRpcSync) and injection into top-level trace.
cardano-rpc/src/Cardano/Rpc/Server/Internal/Monad.hs	Extends MonadRpc environment requirements to include the node-kernel-access IORef.
cardano-rpc/src/Cardano/Rpc/Server/Internal/Env.hs	Extends RpcEnv with rpcNodeKernelAccess reference.
cardano-rpc/src/Cardano/Rpc/Server.hs	Registers SyncService handlers; updates runRpcServer to accept node kernel access ref.
cardano-rpc/src/Cardano/Rpc/Proto/Api/UtxoRpc/Sync.hs	Adds the SyncService proto API module and metadata instances (new).
cardano-rpc/README.md	Updates SyncService method status table for FetchBlock.
cardano-rpc/proto/utxorpc/v1beta/sync/sync.proto	Adds UTxO RPC SyncService proto definitions (new).
cardano-rpc/gen/Proto/Utxorpc/V1beta/Sync/Sync.hs	Adds generated proto-lens Haskell bindings for SyncService (new, generated).
cardano-rpc/gen/Proto/Utxorpc/V1beta/Sync/Sync_Fields.hs	Adds generated field lenses for SyncService messages (new, generated).
cardano-rpc/cardano-rpc.cabal	Exposes new Sync modules and adds generated Sync modules to the gen library stanza.
cardano-api/src/Cardano/Api/Consensus/Internal/Reexport.hs	Adds re-exports of consensus/kernel/ChainDB-related types to support kernel access.
cardano-api/src/Cardano/Api/Consensus.hs	Re-exports additional consensus/kernel/ChainDB-related types and imports ChainDB qualified.
.gitignore	Ignores .serena/.
.changes/20260602_cardano_rpc_fetchblock.yml	Adds changelog fragment for FetchBlock work (needs kind adjustment per review comments).
.changes/20260602_cardano_api_consensus_reexports.yml	Adds changelog fragment for new Cardano.Api.Consensus re-exports.

[carbolymer]

TODO: fix TOCTOU bug - this should be inside single getBlockComponent.