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/java/zb-mom-ww-mxgateway-client/build.gradle

@@ -63,10 +63,11 @@ protobuf {
 // or a plugin/protobuf version bump, silently drifts the committed output. checkGeneratedClean
 // fails when the regenerated tree differs from what is committed.
 //
-// Caveat (repo memory project_java_generated_churn): the protobuf gradle plugin also rewrites
-// MxaccessGateway.java with a spurious protobuf-runtime-version delta on every build even when no
-// .proto changed. CI reverts that one file (git checkout) before invoking this task; locally, do the
-// same when you did not touch a .proto. See docs/GatewayTesting.md "Continuous Integration".
+// The grpc/protobuf toolchain is pinned (build.gradle: grpcVersion / protobufVersion), so a
+// regeneration is byte-identical to the committed single-file aggregates modulo real .proto
+// changes — no spurious protobuf-runtime-version churn (IPC-24 verified this and deleted the old
+// unconditional CI churn-revert step, which masked message-level drift). Regenerate and commit
+// after any .proto change. See docs/GatewayTesting.md "Continuous Integration".
 tasks.register('checkGeneratedClean') {
     group = 'verification'
     description = 'Fails if the committed generated Java tree differs from a fresh regeneration.'
@@ -83,9 +84,9 @@ tasks.register('checkGeneratedClean') {
         def dirty = stdout.toString().trim()
         if (!dirty.isEmpty()) {
             throw new GradleException(
-                "Generated Java is stale or churned:\n${dirty}\n" +
-                "Regenerate and commit after a .proto change, or 'git checkout' the spurious " +
-                "MxaccessGateway.java protobuf-version churn when no .proto changed.")
+                "Generated Java is stale:\n${dirty}\n" +
+                "Regenerate and commit the Java client after a .proto change " +
+                "(gradle :zb-mom-ww-mxgateway-client:generateProto).")
         }
     }
 }