fix(IPC-23,IPC-24,IPC-25,IPC-32): proto-comment regen wave + codegen-freshness guards

Proto comments (comment-only, no wire change):
- mxaccess_worker.proto GatewayHello.max_frame_bytes: every worker->gateway frame
  must serialize within the negotiated max; reply builders truncate (IPC-23).
- mxaccess_gateway.proto DrainEventsReply: count-cap + byte-cap, drain-until-empty
  caller contract (IPC-23).
- mxaccess_gateway.proto ReplayGap.oldest_available_sequence: empty-ring value is
  highest-observed+1, oldest-1 resume formula stays valid (GWC-25 deferred amendment).

Regen wave: Contracts/Generated (C# XML doc), rust vendored protos (byte-copy),
Go bindings (worker binding was genuinely stale - lacked MaxFrameBytes entirely),
Python worker _pb2 (real descriptor delta), Java aggregates (javadoc, zero
protobuf-version churn under the pinned toolchain), client descriptor set.

IPC-24: pinned Java toolchain regenerates with no gencode-version churn, so the
unconditional churn-revert step in ci.yml is a fossil - deleted it; git diff is
now a true message-level drift gate for the single-file Java aggregates.

IPC-25: pin protoc-gen-go v1.36.11 / protoc-gen-go-grpc 1.6.2 in the Go generate
script (+ fix a latent pwsh-7 parse bug); add Check 4 to check-codegen.ps1
(regenerate Go+Python bindings, fail on diff, tool-missing fails not skips); add
the pinned-generator installs to the portable CI job.

IPC-32: relabel check-codegen banners 1/4..4/4 (folded into the Check 4 edit).

Docs: ClientProtoGeneration.md, Contracts.md, GatewayTesting.md, build.gradle
checkGeneratedClean caveat. Tracking: IPC-23/24/25/32 -> Done, GWC-25 proto note
resolved, change-log 2026-08-07.

clients/rust/protos/mxaccess_gateway.proto

@@ -676,6 +676,10 @@ message WorkerInfoReply {
 }
 
 message DrainEventsReply {
+  // The reply is bounded by both a server-side count cap and the negotiated
+  // worker-frame byte cap; a reply may therefore carry fewer events than
+  // `max_events` and fewer than are queued. Callers drain iteratively until an
+  // empty reply.
   repeated MxEvent events = 1;
 }
 
@@ -760,6 +764,11 @@ message ReplayGap {
   // after_worker_sequence = oldest_available_sequence - 1 in the next
   // StreamEventsRequest, which will cause the server to replay starting at
   // oldest_available_sequence (the first retained event).
+  // When nothing is retained (the replay ring is empty), this is the next sequence
+  // that can be delivered — `highest observed + 1` — and the `oldest - 1` resume
+  // formula remains valid: it resolves to the highest sequence already seen, so the
+  // follow-up resume replays nothing, reports no gap, and every newer live event
+  // passes. The interval evicted is unchanged.
   uint64 oldest_available_sequence = 2;
 }
 

clients/rust/protos/mxaccess_worker.proto

@@ -47,6 +47,9 @@ message GatewayHello {
   // instead of a hard-coded default; 0 (an older gateway that never set the field) means
   // "use the worker's built-in default". Sits above the public gRPC cap by an
   // envelope-overhead margin so an accepted gRPC payload always fits one worker frame.
+  // Every worker->gateway frame — events, heartbeats, faults, and control replies
+  // including DrainEvents — must serialize within this limit; reply builders truncate
+  // to fit rather than emit an oversized frame.
   uint32 max_frame_bytes = 4;
 }