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.

scripts/check-codegen.ps1

@@ -1,7 +1,7 @@
 #!/usr/bin/env pwsh
-# Codegen freshness guard for CI (IPC-01, IPC-19, IPC-20, CLI-02).
+# Codegen freshness guard for CI (IPC-01, IPC-19, IPC-20, IPC-25, CLI-02).
 #
-# Three checks, all Linux/macOS-runnable (no Server build, no x86 worker):
+# Four checks, all Linux/macOS-runnable (no Server build, no x86 worker):
 #   1. Published client descriptor set matches the current .proto sources (delegates to
 #      publish-client-proto-inputs.ps1 -Check, which normalizes source_code_info so it is
 #      protoc-version tolerant).
@@ -13,6 +13,12 @@
 #      crate buildable outside the repo, CLI-02) are byte-identical to the canonical Contracts
 #      protos. A drift means a .proto was edited without refreshing the vendored copies, which would
 #      publish a stale wire contract to crate consumers while the in-repo build stays correct.
+#   4. The committed Go and Python client bindings match a fresh regeneration (IPC-25). The two
+#      per-client generate-proto.ps1 scripts pin their generators (protoc-gen-go v1.36.11 /
+#      protoc-gen-go-grpc v1.6.2 for Go; grpcio-tools 1.80.0 for Python), so a clean checkout
+#      regenerates deterministic output; a non-empty git diff means a .proto was edited without
+#      regenerating and committing those bindings. A missing generator FAILS the check (a skipped
+#      guard is the exact silent-drift hole IPC-25 closes), never skips it.
 #
 # The x86 Worker + Worker.Tests are Windows-only and are guarded by the SSH-driven `windows-x86`
 # CI job (see docs/GatewayTesting.md, Continuous Integration), not here.
@@ -28,7 +34,7 @@ $generatedDir = Join-Path $repoRoot 'src/ZB.MOM.WW.MxGateway.Contracts/Generated
 $contractsProject = Join-Path $repoRoot 'src/ZB.MOM.WW.MxGateway.Contracts/ZB.MOM.WW.MxGateway.Contracts.csproj'
 $failures = New-Object System.Collections.Generic.List[string]
 
-Write-Host '== Check 1/2: client descriptor set freshness =='
+Write-Host '== Check 1/4: client descriptor set freshness =='
 try {
     & (Join-Path $PSScriptRoot 'publish-client-proto-inputs.ps1') -Check
     if ($LASTEXITCODE -ne 0) {
@@ -40,7 +46,7 @@ catch {
 }
 
 Write-Host ''
-Write-Host '== Check 2/2: Contracts/Generated matches a fresh regeneration =='
+Write-Host '== Check 2/4: Contracts/Generated matches a fresh regeneration =='
 try {
     # Force a full regeneration: Grpc.Tools skips regen when the committed .cs look up to date, so
     # remove them first (the documented "del Generated/*.cs to force regen" trick).
@@ -66,7 +72,7 @@ catch {
 }
 
 Write-Host ''
-Write-Host '== Check 3/3: Rust vendored protos match canonical Contracts protos =='
+Write-Host '== Check 3/4: Rust vendored protos match canonical Contracts protos =='
 try {
     $canonicalProtoDir = Join-Path $repoRoot 'src/ZB.MOM.WW.MxGateway.Contracts/Protos'
     $vendoredProtoDir = Join-Path $repoRoot 'clients/rust/protos'
@@ -87,6 +93,28 @@ catch {
     $failures.Add("Rust vendored proto check failed: $($_.Exception.Message)")
 }
 
+Write-Host ''
+Write-Host '== Check 4/4: Go and Python client bindings match a fresh regeneration =='
+try {
+    # Regenerate both binding sets with their pinned generators, then diff. The per-client scripts
+    # throw on a missing or off-pin generator, so any failure here FAILS the check rather than
+    # skipping it (a skipped guard is exactly the silent-drift hole IPC-25 closes).
+    $goBindingDir = 'clients/go/internal/generated'
+    $pyBindingDir = 'clients/python/src/zb_mom_ww_mxgateway/generated'
+
+    & (Join-Path $repoRoot 'clients/go/generate-proto.ps1') | Out-Host
+    & (Join-Path $repoRoot 'clients/python/generate-proto.ps1') | Out-Host
+
+    $bindingDiff = (& git -C $repoRoot status --porcelain -- $goBindingDir $pyBindingDir | Out-String).Trim()
+    if (-not [string]::IsNullOrEmpty($bindingDiff)) {
+        Write-Host $bindingDiff
+        $failures.Add("Go/Python client bindings differ from a fresh regeneration. Run clients/go/generate-proto.ps1 and clients/python/generate-proto.ps1 with the pinned generators and commit $goBindingDir and $pyBindingDir.")
+    }
+}
+catch {
+    $failures.Add("Go/Python codegen check failed (tool missing or regeneration error): $($_.Exception.Message)")
+}
+
 Write-Host ''
 if ($failures.Count -gt 0) {
     Write-Host 'Codegen freshness check FAILED:' -ForegroundColor Red