chore(contract): sync ocp protos to ea6418c5 and add a changelog

[bmc08gt]

Picks up ocp-protobuf-api@ea6418c5 — "Add the Balance RPC service (#63)".

The change

One new file, proto/balance/v1/ocp_balance_service.proto. Nothing pre-existing moved, so no message, field, or result enum was renumbered.

service Balance {
    rpc GetBalance(GetBalanceRequest) returns (GetBalanceResponse);
}

message GetBalanceRequest {
    common.v1.SolanaAccountId owner = 1 [(validate.rules).message.required = true];
}

message GetBalanceResponse {
    Result result = 1;
    enum Result { OK = 0; DENIED = 1; NOT_FOUND = 2; }
    uint64 core_mint_value = 2;
}

GetBalanceRequest carries no auth or signature field, unlike every other OCP endpoint. Both app scaffolds implement it that way rather than pattern-matching the neighbours, but if reading any owner's balance unauthenticated was not the intent, this is the moment to catch it.

The generated Swift is committed alongside the proto, produced by the generators pinned in scripts/toolchain.env. No generator version moved, so the Sources/ diff is only the two new Balance files.

Release

Needs publishing at 0.2.0: additive API surface over 0.1.0, which is the only release so far.

Release notes

publish.yml created the release with --generate-notes, which lists merged PR titles. That is why 0.1.0 released with a body containing nothing but a "Full Changelog" link: a consumer reading it cannot tell what is in the API.

Notes now come from the CHANGELOG.md section matching the version being published, written here in the sync PR while the contract diff is still at hand. A version with no section fails the publish, and it fails in an early step, before anything is uploaded, because Maven Central will not accept a version number twice.

flipcash2-client-protocol had the same gap and the same workflow. code-payments/flipcash2-client-protocol#4 mirrors this half, so the two publish workflows stay identical apart from names and coordinates.

Both consumer PRs already pin 0.2.0 and are drafts until it exists:

• feat(opencode): scaffold Balance service for GetBalance code-android-app#1334
• feat(payments): scaffold Balance service for GetBalance code-ios-app#658