[bmc08gt]

Server-mediated stablecoin swaps now build CoinbaseStableSwapper SwapV2 and send swap_version = 2. This matches code-payments/ocp-server#278, where the server builds whichever instruction the request names and the client rebuilds and signs the same transaction.

The ocp-client-protocol pin is at 0.9.0 (3fef1e0), which carries swap_version.

What changed

• CoinbaseStableSwapperProgram_SwapV2 is new. It uses discriminator [43, 4, 237, 11, 26, 201, 30, 98] and the v1 swap args. Its 15 accounts are v1's 16 with the whitelist (index 12) removed.
• The v1 path is removed: CoinbaseStableSwapperProgram_Swap, _SwapForVersion, the builders' swapVersion parameter, and the whitelist PDA derivation. Every swap the app builds is SwapV2; SERVER_SWAP_VERSION stays as the value sent in swap_version.
• SERVER_SWAP_VERSION = 2 feeds both the request field and the local builder, so the two cannot disagree.
  • Stateful: StatefulSwapRequest.stablecoinParams() and buildStablecoinSwapperInstructions.
  • Stateless: IntentStatelessSwap.stablecoinParams() and buildStatelessSwapInstructions.
• The client-built deposit swaps (UsdfDepositInstructions, UsdcToUsdfSwapInstructions, both reached from PhantomWalletController) build SwapV2 too, without a version switch. The server never sees these transactions, so there is no swap_version to match.

Tests

• CoinbaseStableSwapperProgramTest asserts the exact bytes and account list from the server's instructions_swap_v2_test.go. iOS asserts the same vector.
• CoinbaseStablecoinSwapperInstructionsTest and StatelessSwapInstructionsTest check that both builders emit the 15-account SwapV2.
• StablecoinSwapVersionRequestTest checks that both requests carry swap_version = 2.
• ClientBuiltDepositSwapV2Test checks that both deposit builders emit the 15-account SwapV2.
• CoinbaseStablecoinDepositTransactionTest pins the full encoded deposit transaction. Its SwapV2 bytes pass simulateTransaction on mainnet (Swapped 5000000 tokens, 59730 compute units), so mainnet CoinbaseStableSwapper accepts swap_v2 on the deposit path.

Before merging

• Add support for swap v2 for the Coinbase Stableswapper ocp-server#278 is deployed. It had to be: an older server ignores swap_version and builds Swap, so the signed SwapV2 transaction wouldn't match.
• On the stateful path, swap_version is also inside the signed proof's client_parameters, via verifiedMetadata(). That needs a confirmation from the server side that this is accepted.

Linked: iOS code-payments/code-ios-app#1104