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/go/internal/generated/mxaccess_gateway.pb.go

@@ -5974,8 +5974,12 @@ func (x *WorkerInfoReply) GetMxaccessClsid() string {
 }
 
 type DrainEventsReply struct {
-	state         protoimpl.MessageState `protogen:"open.v1"`
-	Events        []*MxEvent             `protobuf:"bytes,1,rep,name=events,proto3" json:"events,omitempty"`
+	state protoimpl.MessageState `protogen:"open.v1"`
+	// 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.
+	Events        []*MxEvent `protobuf:"bytes,1,rep,name=events,proto3" json:"events,omitempty"`
 	unknownFields protoimpl.UnknownFields
 	sizeCache     protoimpl.SizeCache
 }
@@ -6411,6 +6415,11 @@ type ReplayGap struct {
 	// 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.
 	OldestAvailableSequence uint64 `protobuf:"varint,2,opt,name=oldest_available_sequence,json=oldestAvailableSequence,proto3" json:"oldest_available_sequence,omitempty"`
 	unknownFields           protoimpl.UnknownFields
 	sizeCache               protoimpl.SizeCache