Phase 2: d14n service restructuring — remove deprecated services and RPCs

[neekolas]

Summary

Complete the d14n service restructuring by removing all deprecated RPCs and services introduced in Phase 1 (#328). This is the breaking-change phase — it should only land after all consumers have migrated to the new service endpoints.

Parent issue: #327

Prerequisites

Before this work begins, the following must be true:

• All nodes use ReplicationApi.SubscribeOriginators instead of SubscribeEnvelopes
• All clients use QueryApi for queries/subscriptions instead of ReplicationApi
• All gateways use PublishApi.PublishPayerEnvelopes instead of ReplicationApi.PublishPayerEnvelopes
• All clients use gateway_api.GatewayApi instead of payer_api.PayerApi
• Node auth token enforcement is ready for ReplicationApi

Scope

All changes are within proto/xmtpv4/.

1. Remove deprecated RPCs from ReplicationApi

File: proto/xmtpv4/message_api/message_api.proto

Remove the following deprecated RPCs from the ReplicationApi service:

• SubscribeEnvelopes
• SubscribeTopics
• QueryEnvelopes
• PublishPayerEnvelopes
• GetInboxIds
• GetNewestEnvelope

After removal, ReplicationApi should contain only:

service ReplicationApi {
  rpc SubscribeOriginators(SubscribeOriginatorsRequest)
      returns (stream SubscribeOriginatorsResponse) {}
}

2. Clean up orphaned message types

After removing the deprecated RPCs, evaluate whether the following message types are still needed in message_api.proto (they may only be referenced by the new service files via import):

• EnvelopesQuery — used by SubscribeEnvelopesRequest and QueryEnvelopesRequest
• SubscribeEnvelopesRequest / SubscribeEnvelopesResponse — used by deprecated SubscribeEnvelopes and NotificationApi

Keep any types still referenced by QueryApi, PublishApi, or NotificationApi. Remove types that are no longer imported by any service.

3. Delete payer_api package

Delete: proto/xmtpv4/payer_api/payer_api.proto (and directory)

Prerequisite: gateway_api.GatewayApi currently imports message types from payer_api. Before deletion:

1. Move PublishClientEnvelopesRequest, PublishClientEnvelopesResponse, GetNodesRequest, GetNodesResponse into proto/xmtpv4/gateway_api/gateway_api.proto
2. Update GatewayApi RPC signatures to reference the local types
3. Remove the payer_api import

4. Update buf.yaml

• Remove any RPC_REQUEST_RESPONSE_UNIQUE ignore entries for files that no longer have shared types after deprecated RPCs are removed
• Remove any RPC_RESPONSE_STANDARD_NAME ignore entries that are no longer needed
• Verify buf lint is clean (or only has pre-existing warnings unrelated to xmtpv4)

5. Enforce ReplicationApi auth (proto-side, if applicable)

If node auth token enforcement requires proto-level changes (e.g., metadata annotations or interceptor configuration), add them to ReplicationApi. Otherwise, this is a server-side concern only and can be skipped in the proto repo.

Verification

cd proto && buf lint && buf build
cd proto && buf breaking --against '.git#subdir=proto'  # expect breaking changes
grep -r "payer_api" proto/  # should return no results

The buf breaking check will flag breaking changes (removed RPCs, deleted package). This is intentional and expected.

Out of scope

• Server-side implementation changes
• Client SDK migration
• Changes to metadata_api, misbehavior_api, or envelopes