Context

Part 1 of #6510. Pure refactoring — no behavior change.

This refactoring is necessary to enable the realisation of #6511 in a way that is robust (statically checked). Check #6510 for more details.

This PR is meant to be a pure refactoring — there should be no behaviour changes.

Originally #6512 proposed extracting testnet path conventions into a new cardano-testnet-paths micro-package. However, since both cardano-testnet and tx-generator already depend on cardano-node, we can place the shared path definitions directly in the cardano-node package instead. This avoids introducing a new package while achieving the same compile-time safety for directory layout conventions.

Unused path definitions will be dead-code eliminated by GHC and won't appear in the cardano-node executable.

This replaces #6512.

Changes

New: module in cardano-node (e.g. Cardano.Node.Testnet.Paths)

Add a new module to the cardano-node library. Depends only on base and filepath (already available). Exports:

defaultNodeName      :: Int -> String        -- "node" <> show n
defaultNodeDataDir   :: Int -> FilePath       -- "node-data" </> defaultNodeName n
defaultUtxoKeyDir    :: Int -> FilePath       -- "utxo-keys" </> "utxo" <> show n
defaultUtxoSKeyPath  :: Int -> FilePath       -- defaultUtxoKeyDir n </> "utxo.skey"
defaultUtxoVKeyPath  :: Int -> FilePath       -- defaultUtxoKeyDir n </> "utxo.vkey"
defaultUtxoAddrPath  :: Int -> FilePath       -- defaultUtxoKeyDir n </> "utxo.addr"
defaultSocketDir     :: FilePath              -- "socket"
defaultSocketName    :: FilePath              -- "sock"
defaultSocketPath    :: Int -> FilePath       -- defaultSocketDir </> defaultNodeName n </> defaultSocketName
defaultConfigFile    :: FilePath              -- "configuration.yaml"
defaultPortFile      :: Int -> FilePath       -- defaultNodeDataDir n </> "port"

Modify: cardano-testnet/src/Testnet/Defaults.hs

Import and re-use defaultNodeName, defaultNodeDataDir from the new module instead of defining locally. defaultUtxoKeys delegates to defaultUtxoSKeyPath and defaultUtxoVKeyPath for path construction.

Modify: cardano-testnet/src/Testnet/Runtime.hs

Import defaultSocketDir, defaultSocketName from the new module instead of using bare "socket" and "sock" string literals.

Modify: cardano-testnet/src/Testnet/Filepath.hs

Import defaultSocketDir from the new module instead of using bare "socket" string literal.

Modify: cardano-testnet/src/Testnet/Start/Cardano.hs

Import defaultConfigFile and defaultUtxoAddrPath from the new module instead of using inline string literals.

Modify: cardano-testnet/cardano-testnet.cabal

No new dependency needed — cardano-testnet already depends on cardano-node.

Advantages over #6512

• No new package (cardano-testnet-paths) to create and maintain
• No changes to cabal.project
• Both consumers (cardano-testnet, tx-generator) already depend on cardano-node
• GHC prunes unused definitions from the node executable — no binary size or runtime cost