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.

archreview/2026-07-12/remediation/10-gateway-core.md

@@ -61,7 +61,7 @@ Coordinate with (do not block on) open GWC-21: if `EventChannelFullModeTimeout`
 
 The proto comment currently states "`oldest_available_sequence` itself IS still retained", which becomes false in the empty-ring case — per the docs-with-source rule, amend the field comment in the same commit to define the empty-ring value ("when nothing is retained, this is the next sequence that can be delivered — `highest observed + 1` — and the `oldest − 1` resume formula remains valid; the interval evicted is unchanged"). This is a comment-only proto change (no descriptor delta), but the repo's codegen rules still apply — see the steps.
 
-**Implementation.**
+**Implementation.** (Code + `docs/Sessions.md` landed 2026-08-07 on `fix/gwc-25-replaygap-trio`; the deferred proto-comment amendment below **landed 2026-08-07** with the IPC-23 codegen wave on `fix/ipc-24-25-codegen` — GWC-25 is fully resolved.)
 - `Sessions/SessionEventDistributor.cs:463-467`: replace `oldestAvailableSequence = 0;` with `oldestAvailableSequence = gap ? _highestSequenceSeen + 1 : 0;` plus a comment explaining the `oldest − 1` client formula this must keep valid (cite this finding).
 - `src/ZB.MOM.WW.MxGateway.Contracts/Protos/mxaccess_gateway.proto` (`ReplayGap.oldest_available_sequence`, ~line 759): append the empty-ring sentence above. Then regenerate per repo rules: delete `src/ZB.MOM.WW.MxGateway.Contracts/Generated/*.cs`, `dotnet build src/ZB.MOM.WW.MxGateway.Contracts/ZB.MOM.WW.MxGateway.Contracts.csproj`, and **commit `Generated/`** (net48 worker builds break otherwise). Sync the vendored client copies of the proto byte-identical (`clients/*/`); a comment-only edit changes no descriptor, so: Python `*_pb2*` output is unchanged (comments are not embedded — regenerate with the pinned grpcio-tools only if the files actually differ), Go/C#/Rust generated doc comments will churn — regenerate those per each client README, and revert spurious Java aggregate-file churn if no message-level delta appears (per the established Java convention).
 - `docs/Sessions.md` (~lines 228-234, ReplayGap section): document the empty-ring sentinel value and that `after_worker_sequence = oldest_available_sequence − 1` is the universal resume formula in both the retained and fully-evicted cases.