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mxaccessgw/archreview/2026-07-12/remediation/00-tracking.md
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Joseph Doherty 404f7cd993 docs(archreview): close GWC-28, GWC-29, GWC-30, TST-28
Flip the four findings to Done in the 2026-07-12 tracking registers
(Gateway core + Testing) and in the per-domain registers of
10-gateway-core.md and 60-testing-docs-gaps.md; append the 2026-08-07
change-log row recording what shipped, the pre-fix red for GWC-28, and
the TST-28 mutation check.
2026-08-07 06:15:45 -04:00

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MxAccessGateway — Remediation Tracking (2026-07-12 review)

Master progress tracker for the 2026-07-12 follow-up architecture review. Generated 2026-07-13.

Source review: ../00-overall.md · Per-domain remediation designs are linked below and hold the full Finding / Impact / Design / Implementation / Verification for every entry here. The first-cycle tracker (../../remediation/00-tracking.md) remains the record for the original 153 findings; this document tracks only the 47 new IDs (GWC-24+, WRK-21+, IPC-23+, SEC-31+, CLI-35+, TST-25+) plus the old-tracker actions listed at the end.

How to use this document

  • Each finding has a stable ID that never changes. Cite it in commits, branches, and PRs (e.g. fix(GWC-25): empty-ring ReplayGap sentinel).
  • The Status column is the single source of truth for progress. Update it in the same change that lands the fix.
  • Do the work in roadmap-tier order (P0 → P1 → P2), respecting the Dep column and the cross-cutting clusters below — several fixes are one change set across two domains and must land together.
  • When a fix lands: flip Status to Done and, per the repo rule, update the affected docs in the same commit.

Status legend: Not started · In progress · In review · Done · Won't fix (record why in the domain doc) · N/A (informational / decision recorded, no action).

Severity roll-up

Domain Doc High Medium Low Info Total
Gateway core 10-gateway-core.md 2 4 1 7
Worker 20-worker.md 1 7 8
Contracts & IPC 30-contracts-ipc.md 3 5 2 10
Security & dashboard 40-security-dashboard.md 1 4 1 6
Clients 50-clients.md 5 6 11
Testing, docs & gaps 60-testing-docs-gaps.md 1 2 3 6
Total 1 14 29 4 48

Roadmap-tier roll-up

Tier Meaning Count Findings
P0 Correctness & safety — all small-to-medium 10 GWC-25, WRK-21, IPC-23, IPC-24, IPC-25, IPC-30, SEC-31, SEC-32, CLI-35, CLI-36
P1 Process & hardening 12 GWC-24, WRK-26, SEC-33, SEC-36, CLI-37, CLI-38, CLI-39, CLI-42, CLI-45, TST-25, TST-26, TST-27
P2 Completeness & polish 10 GWC-26, GWC-27, GWC-28, WRK-25, IPC-26, IPC-27, SEC-34, TST-28, TST-29, TST-30
Not individually in the roadmap (Lows/Infos) 16 GWC-29/30, WRK-22/23/24/27/28, IPC-28/29/31/32, SEC-35, CLI-40/41/43/44

P0 — do first (10)

Sequenced by cluster; a cluster is one change set.

ID Sev Eff Dep Status Title
GWC-25 Medium S CLI-35/36 (coord) Done Empty-ring ReplayGap sentinel carries oldest_available_sequence = 0, dead-streaming a compliant client
CLI-35 Medium S GWC-25 (coord) Done Python CLI stream-events crashes on a ReplayGap
CLI-36 Medium S GWC-25 (coord) Done Go CLI stream-events silently destroys the ReplayGap signal
WRK-21 Medium M owns IPC-23 fix; WRK-28 same batch Not started DrainEvents bound is count-based only; oversized reply kills the session and loses the drained events
IPC-23 Medium S WRK-21 Not started DrainEvents contract requirements (reply fits negotiated max, no event loss, drain-until-empty) + proto-comment/doc wave
IPC-30 Low M WRK-21 (same batch) Not started Oversized event frame stays session-fatal by design, but the death becomes structured (fault frame + logged identity)
SEC-31 Medium M Not started Failure limiter partitions on attacker-controlled key id and blocks before verification (lockout DoS)
SEC-32 Low S SEC-31 Not started Failure-limiter LRU flushable by junk-token spray; token prefix never validated
IPC-24 Medium S Not started CI's unconditional Java churn-revert masks real drift
IPC-25 Medium M Not started Regenerate stale Go/Python worker bindings + add binding-freshness guard (Check 4) to check-codegen.ps1

Finding registers by domain

Full design + implementation for each row lives in the linked domain doc under its ID heading.

Gateway core — 10-gateway-core.md

ID Sev Tier Eff Dep Status Title
GWC-24 Medium P1 M GWC-21 (coord, old tracker) Done Unbounded event staging channel: sustained slow drain grows memory silently and invisibly
GWC-25 Medium P0 S CLI-35/36 (coord) Done Empty-ring ReplayGap sentinel carries oldest_available_sequence = 0
GWC-26 Low P2 M GWC-27 Done Alarm monitor attaches its subscriber after SubscribeAlarms; window transitions bypass the feed
GWC-27 Low P2 S GWC-26 Done AttachInternalEventSubscriber bypasses the readiness gate; premature attach poisons the distributor
GWC-28 Low P2 S GWC-10 (coord, old tracker) Done Gateway→worker envelope sequence stamped at creation, not at write
GWC-29 Low S Done Invoke deep-clones the entire request only to discard the cloned command
GWC-30 Info S Done Frame reader allocates a fresh 4-byte length-prefix array per frame

Worker — 20-worker.md

ID Sev Tier Eff Dep Status Title
WRK-21 Medium P0 M IPC-23 (fix owned here); WRK-28 Not started DrainEvents bound count-based only; oversized reply kills session and loses drained events
WRK-22 Low S IPC-26 (fix owned here) Not started Cancelled WriteAsync leaves its frame queued; it is still written later
WRK-23 Low S WRK-21 Not started Rejected frames consume sequence numbers, producing wire gaps
WRK-24 Low S Not started AdoptNegotiatedMaxMessageBytes has no lower-bound sanity check
WRK-25 Low P2 S WRK-22 (shared seam) Not started WRK-12 flush coalescing never engages on the event hot path
WRK-26 Low P1 S WRK-23 (soft); discharges IPC-29 Not started Write-priority and overflow doc drift from the WRK-07 change
WRK-27 Low S Not started Alarm poll bypasses the watchdog's in-flight suppression (15 s vs 75 s)
WRK-28 Low S WRK-21 (same batch) Not started 10,000 drain cap is a duplicated magic constant

Contracts & IPC — 30-contracts-ipc.md

ID Sev Tier Eff Dep Status Title
IPC-23 Medium P0 S WRK-21 (mechanics) Not started DrainEvents byte-blindness — contract requirements + proto-comment/doc wave
IPC-24 Medium P0 S Not started CI's unconditional Java churn-revert masks real drift
IPC-25 Medium P0 M Not started Stale Go/Python worker bindings: regenerate (pinned toolchains) + check-codegen Check 4
IPC-26 Low P2 S WRK-22 (mechanics) Not started Cancelled write leaves ghost frame — cancelled means never written
IPC-27 Low P2 S Not started Descriptor-freshness test blind to enums/services/galaxy descriptor
IPC-28 Low S Not started docs/Grpc.md missing CommandTooLarge → ResourceExhausted mapping
IPC-29 Low S WRK-26 (discharged by) Not started WorkerFrameProtocol.md missing write-scheduling/sequencing section
IPC-30 Low P0 M WRK-21 (same batch) Not started Oversized event frame: keep session-fatal, make the death structured
IPC-31 Info N/A Gateway creation-time sequence stamping accepted; diagnostic-only, decision recorded
IPC-32 Info S IPC-25 (folded in) Not started check-codegen banner relabel 1/4…4/4

Security & dashboard — 40-security-dashboard.md

ID Sev Tier Eff Dep Status Title
SEC-31 Medium P0 M Not started Failure limiter: composite (peer, key-id) partitions + cross-peer aggregate with probe admission
SEC-32 Low P0 S SEC-31 Not started Limiter LRU flushable by junk-token spray; validate token shape, cap per-peer partitions
SEC-33 Low P1 M old SEC-23 (co-locate) Not started Host-meaningful path rooting; drop Windows literals from appsettings; validate Galaxy SnapshotCachePath
SEC-34 Low P2 S Not started Verification cache: expiry outlives TTL; Invalidate races in-flight repopulation
SEC-35 Info S N/A Production hard-stops key on exact Production environment name (doc-only)
SEC-36 Low P1 M cross-repo scadaproj/infra/glauth Not started Committed dev LDAP service-account password: rotate, remove, move dev channel to user-secrets

Clients — 50-clients.md

ID Sev Tier Eff Dep Status Title
CLI-35 Medium P0 S GWC-25 (coord) Done Python CLI stream-events crashes on a ReplayGap
CLI-36 Medium P0 S GWC-25 (coord) Done Go CLI stream-events silently destroys the ReplayGap signal
CLI-37 Medium P1 M CLI-38 (co-land) Not started Status-array validation must branch on category per the proto contract (4-vs-1 divergence)
CLI-38 Medium P1 S Not started Align .NET/Go/Java on hresult < 0 — lands old CLI-08, cures design-doc drift
CLI-39 Medium P1 S CLI-35..38, CLI-45 (land last) Not started Bump client versions off published 0.1.2 (converge on 0.2.0); registry-collision guard in pack-clients.ps1
CLI-40 Low M Not started Port the exact-secret credential scrub to Rust/Java/.NET
CLI-41 Low M Not started Uniform malformed-reply contract for AuthenticateUser/ArchestrAUserToId/AddBufferedItem
CLI-42 Low P1 S Not started Document the vendored Rust proto layout (CLI-02's missing doc half)
CLI-43 Low S Not started Java style guide still prescribes "Java 21 preferred"
CLI-44 Low S Not started Go event goroutine can mislabel a genuine terminal error as ErrSlowConsumer
CLI-45 Low P1 M Not started Standardize CLI credential env-var names; fail fast on missing/empty passwords

Testing, docs & gaps — 60-testing-docs-gaps.md

ID Sev Tier Eff Dep Status Title
TST-25 High P1 M unlocks old TST-05, TST-24 Done Windows/x86 test tier has zero automation — SSH-driven windev CI job
TST-26 Medium P1 S TST-25 (same commit) Done Docs/scripts describe removed CI jobs; Generated/-guard reattributed to check-codegen
TST-27 Medium P1 S Not started ShowTagValues config row still says "Reserved" after SEC-25 made the flag live
TST-28 Low P2 S relates IPC-02 (old) Done Gateway-side max_frame_bytes handshake untested in the CI-run suite
TST-29 Low P2 S Done Retire oldtasks.md (fold Phase-5 governance into DesignDecisions.md); delete root artifacts
TST-30 Low P2 M Not started Single shared Gitea runner is a CI throughput/availability bottleneck (cross-repo contention, no run cancel/delete API)

Cross-cutting clusters

Sequence these together rather than piecemeal — several are one change set spanning two domains:

  • Drain / oversized-frame cluster (P0): WRK-21 + IPC-23 + IPC-30, with WRK-28 and WRK-23 in the same batch. One worker change set in WorkerPipeSession.cs/WorkerFrameWriter.cs; WRK-21 owns the byte-budgeted drain and must satisfy IPC-23's requirements R1R3; IPC-30's structured-fault seam lands in the same drain loop. IPC-23's proto-comment edits trigger the full regen fan-out (Generated/, Rust vendored, Go/Java, descriptor set) — land with WRK-21 so the wave happens once. One windev x86 verification run for the cluster.
  • ReplayGap end-to-end (P0): GWC-25 (server sentinel arithmetic) + CLI-35 (Python CLI) + CLI-36 (Go CLI). Independently landable; the e2e resume walk validates only when all three are in.
  • Auth limiter (P0): SEC-31 + SEC-32 — same component, one change set, one test suite.
  • Codegen freshness (P0): IPC-24 + IPC-25 (+ IPC-32 folded in). Both edit .gitea/workflows/ci.yml — coordinate the branch with TST-25, which touches the same file.
  • Windows-tier automation (P1): TST-25 + TST-26 (same commit). Unlocks old TST-05/TST-24 and provides CI evidence for every windev-verified cluster above; until it lands, record windev runs in this tracker's change log.
  • Client conformance + release train (P1): CLI-37 + CLI-38 co-land (one conformance commit; closes old CLI-08), then CLI-45, with CLI-40/41 fixtures as follow-ups; CLI-39 lands last so published 0.2.0 carries the conformant behavior. Shared fixtures under clients/proto/fixtures/behavior/; update CrossLanguageSmokeMatrix.md/ClientLibrariesDesign.md same-commit. Do not republish regenerated bindings (IPC-25) before CLI-39 resolves.
  • Doc-drift batch (P1): TST-27 + WRK-26 (discharges IPC-29) + CLI-42 + IPC-28 + SEC-35's doc note — one sweep commit is fine.
  • Backpressure follow-on (P1): GWC-24 — Done 2026-08-07. Landed without a new config key (the staging bound is derived as 2 × EventChannelCapacity), so still-open old GWC-21 (EventChannelFullModeTimeout configurability) remains the natural companion knob but was not a blocker.

Old-tracker actions (../../remediation/00-tracking.md)

  • Close CLI-24 and CLI-34 as Done (incidentally fixed; evidence in ../50-clients.md).
  • When CLI-38 lands, close old CLI-08 with a pointer here.
  • When WRK-26 lands, its doc section also discharges the WorkerFrameProtocol gap; when TST-25 lands, revisit old TST-05 (scheduled live smoke) and TST-24 (client wire tests), which it unlocks.

Change log

Date Change
2026-07-13 Initial tracking doc generated from the six domain remediation designs. All 47 findings Not started (IPC-31, SEC-35 N/A).
2026-07-13 TST-25/TST-26 → In progress (branch fix/tst-25-windev-ci). Added scripts/ci/{windev-worker-ci.ps1,run-windev-ci.sh,windev.known_hosts}, windows-x86 (per-push) + nightly-windev (scheduled) jobs in ci.yml, and the TST-26 doc/comment fixes (GatewayTesting.md, Contracts.md, check-codegen.ps1). Mechanism hand-verified on windev: build→0, bogus-SHA→nonzero (lock released), test→356 passed/0 failed in ~50s (per-push stays test, no demotion), and run-windev-ci.sh SSH+EncodedCommand exit-code propagation confirmed.
2026-07-13 Operator bring-up complete: dedicated CI ed25519 key installed in windev administrators_authorized_keys (authorized into dohertj2, which owns the working MXAccess/toolchain env — a fresh OS account would break the build; the key is independently revocable), Gitea secrets WINDEV_SSH_KEY/WINDEV_SSH_KNOWN_HOSTS + variable WINDEV_SSH_USER=dohertj2 stored, runner→10.100.0.48:22 egress verified on the traefik net, issue-write confirmed. TST-25/TST-26 → Done: credentialed windows-x86 ran GREEN on d769244 (Gitea run #37) — Linux runner SSHed windev, checked out the SHA in C:\build\mxaccessgw-ci under lock, ran the x86 Worker build + Worker.Tests, exit 0; nightly-windev correctly skipped on the push event. Branch merged to main. Follow-ups (old tracker): revisit TST-05 (scheduled live smoke — now covered by nightly-windev) and TST-24 (client wire tests) which this unlocks.
2026-07-13 Ran the TST-25 acceptance checks (scripts/ci/README.md) — they caught two real CI defects, both fixed on fix/tst-25-ci-key-log-leak: (1) CI SSH key leaked in cleartext in the windows-x86 step env echo (Gitea's line-oriented masker missed the multiline PEM) — rotated the CI key on windev (old pubkey revoked), stored the key base64-encoded so the masker redacts it to *** (confirmed on run #38), taught run-windev-ci.sh to decode, dropped the redundant public known-hosts secret from the job env; (2) bootstrap lock racerun-windev-ci.sh's pre-hand-off git fetch/checkout ran outside the worktree lock, so concurrent runs collided on .git/index.lock; the bootstrap now holds the lock (ps1 re-uses it via MXGW_CI_LOCK_HELD), retest confirmed clean serialization. Also deflaked SessionManagerTests fail-fast timing assertions (absolute <100ms wall-clock bound flaked under CI load; now anchored to the configured timeout / dropped for the zero-timeout case). Checks passed: unreachable-host fast-fail (exit 255/15s), deliberate-red propagation (Worker.Tests failure → exit 1), lock concurrency (2nd run waits), no-key-in-logs (masked). Merge target df7e20d verified GREEN via the local windev path (Worker build + 356 tests); merged to main 19cbf7b. Check 6 (forced-failure nightly issue): issue endpoint+token proven live at bring-up (#124); in-CI forced-failure probe abandoned to shared-runner congestion (residual if: failure() gating is standard Actions).
2026-07-13 New finding TST-30 (Low/P2) added — surfaced during TST-25 acceptance: CI runs on a single shared gitea-runner (maxParallel=1, co-located 10.100.0.35) interleaved with dohertj2/lmxopcua, and Gitea 1.26 exposes no run cancel/delete, so queue latency is unbounded under cross-repo contention and the runner is a single point of failure. Design: add a second/labelled runner + document the no-cancel reality and the run-windev-ci.sh bypass. Roll-ups updated (Testing Low 2→3, total 47→48; P2 9→10).
2026-08-07 TST-29 → Done: migrated the Phase-5 (orphan-worker reattach) deferred-not-planned governance record and the settled Phase-4 Viewer-default decision from oldtasks.md into a new "Session-Resilience Epic Scope" entry in docs/DesignDecisions.md; repointed CLAUDE.md and stillpending.md:7,165 from oldtasks.md to docs/DesignDecisions.md / docs/plans/2026-06-15-session-resilience.md.tasks.json; git rm oldtasks.md. The five untracked root docs-review artifacts (MxAccessGateway-docs-{issues,fixed,final}.md, MxGatewayClient-docs-{issues,fixed}.md) were absent from this worktree — delete from the main working tree separately.
2026-08-07 GWC-24 → Done (branch fix/gwc-24-staging-bound). WorkerClient._eventStaging is now Channel.CreateBounded at 2 × EventChannelCapacity (Wait, single reader/writer, no sync continuations); a rejected staging TryWrite faults the client ProtocolViolation with QueueOverflow("worker-event-staging") unless IsTerminalState() (shutdown stays a silent drop), so a consumer draining slower than its worker produces dies at a fixed ceiling instead of growing gateway memory. Queue-depth accounting moved from EnqueueWorkerEventAsync to StageWorkerEvent, so the single gauge reports staged + queued; the timed-write fault (EventChannelFullModeTimeout / QueueOverflow("worker-events")) is unchanged and still catches the full-stall case first. No new config key — total gateway-side buffering is 3 × MxGateway:Events:QueueCapacity, derived; coordination with still-open old GWC-21 (EventChannelFullModeTimeout configurability) remains open and was not blocked on. Docs same commit: GatewayProcessDesign.md (two overflow faults), MxAccessWorkerInstanceDesign.md, GatewayConfiguration.md, Metrics.md. Tests: WorkerClientTests.StagingChannelOverflowFaultsWorkerWithoutWaitingForFullModeTimeout and .WorkerEventQueueDepthGaugeCountsStagedEvents; WorkerClientTests 22/22 green, NonWindows.slnx builds with 0 warnings.
2026-08-07 ReplayGap end-to-end cluster (GWC-25 + CLI-35 + CLI-36) → Done on fix/gwc-25-replaygap-trio. GWC-25: SessionEventDistributor.RegisterWithReplay's empty-ring branch now reports oldestAvailableSequence = _highestSequenceSeen + 1 when gap == true (still 0 when no gap), so the universal oldest - 1 resume formula no longer wraps to ulong.MaxValue and dead-stream the subscriber; docs/Sessions.md documents the empty-ring value. CLI-35: the Python CLI renders a ReplayGap as a {"replayGap": {...}} row via a new _event_row helper instead of crashing in MessageToDict. CLI-36: the Go CLI branches on result.IsReplayGap() and prints the typed REPLAY_GAP requested_after=<n> oldest_available=<n> line / replayGap JSON row instead of formatting the library's cleared Event. docs/CrossLanguageSmokeMatrix.md gained a per-CLI gap-rendering table (one edit covering both client findings). Four new tests as designed (3 × SessionEventDistributorTests, GatewayEndToEndReconnectReplayTests.ReconnectAfterFullAgeEvictionResumesWithSentinelFormula) plus test_stream_events_renders_replay_gap (Python) and TestRunStreamEventsPrintsReplayGap (Go); all written red first and each reproducing its defect verbatim. Deferred: GWC-25's ReplayGap.oldest_available_sequence proto-comment amendment is not in this change — it is comment-only but triggers the full five-client regen fan-out, so it lands with the later codegen wave (alongside IPC-23's proto-comment edits) rather than forcing a regen for one sentence. Note for that wave: the fake-worker gateway e2e suite cannot run on the macOS worktree without TMPDIR shortened (macOS caps the Unix-domain-socket path backing .NET named pipes at 104 chars; TMPDIR=/tmp dotnet test … works and was used here).
2026-08-07 GWC-27 → Done, GWC-26 → Done (branch fix/gwc-26-27-alarm-attach). GWC-27: GatewaySession.AttachInternalEventSubscriber now mirrors AttachEventSubscriber's readiness gate under _syncRoot, before EnsureDistributorCreated, so a premature attach can no longer latch a poisoned distributor. GWC-26: the alarm monitor takes its internal lease directly from the session before SubscribeAlarms and drains it after the first reconcile; ISessionManager.ReadAlarmEventsAsync removed (zero remaining callers); ApplyReconcile now broadcasts an Acknowledge feed transition for a both-present alarm whose state advanced to ActiveAcked (feed-level repair on AlarmFeedMessage, not MxEvent synthesis). New tests GatewaySessionTests.AttachInternalEventSubscriberBeforeReadyThrowsAndDoesNotPoisonDistributor and GatewayAlarmMonitorAttachOrderTests (TransitionsDuringSubscribeWindow_StillReachTheAlarmFeed, ApplyReconcileBroadcastsAcknowledgeDelta); the alarm-monitor fakes now hand the monitor a real Ready GatewaySession with a dashboard mirror so the window is actually reproducible. Verification: NonWindows build 0 warnings/0 errors; GatewayAlarmMonitor 16 passed, SessionManagerTests 38 passed, GatewaySessionTests 19 passed, AlarmFailoverEndToEndTests 2 passed.
2026-08-07 Code review of fix/gwc-26-27-alarm-attach surfaced a known pre-existing characteristic, now documented: the alarm monitor's reconcile-derived feed repairs are at-least-once, not exactly-once. A reconcile reads the worker's current state while the matching live transition may still be buffered in the monitor's internal lease, so both broadcast and the duplicates are indistinguishable on the alarm feed (StreamAlarms + dashboard alarm hub). This pre-dates GWC-26 — the Raise/Clear presence repair has always had it, since nothing serializes a reconcile pass against the in-flight live stream — so closing it (reconcile/live serialization or transition-timestamp dedup) was ruled out of scope for a P2 fix. Documented instead in GatewayAlarmMonitor.ApplyReconcile, gateway.md, and docs/Sessions.md, with the consumer-side contract stated explicitly (apply transitions idempotently — "set this alarm to this state", never increment/toggle). Candidate finding for the next review cycle.
2026-08-07 GWC-28, GWC-29, GWC-30, TST-28 → Done (branch fix/gwc-28-29-30-polish). GWC-28: WorkerClient.WriteLoopAsync now stamps envelope.Sequence = unchecked(++_nextSequence) immediately before _writer.WriteAsync, and CreateEnvelope leaves it unset; _nextSequence dropped from long + Interlocked to a plain ulong touched only by the write loop (the channel's single consumer, SingleReader = true), so wire order and sequence order are the same thing by construction. Mirrors the worker's WRK-04 stamping, which the gateway half had never received; gateway.md's envelope-sequence rule now states that both sides stamp at write inside their single write path and that inbound enforcement (still open, old GWC-10) would rely on it. New WorkerClientTests.ConcurrentInvokesEmitStrictlyIncreasingSequencesOnTheWire (32 parallel invokes, sequences asserted strictly increasing in wire order) failed 3/3 pre-fix. GWC-29: added MxAccessGrpcMapper.MapCommand(MxCommand); Invoke no longer deep-clones the whole MxCommandRequest just to overwrite and discard its command. The one clone inside MapCommand stays and is documented as required — commandToInvoke may be the gRPC-owned request.Command and is read again after dispatch by TrackCommandReply, so it is what keeps CreateCommandEnvelope's no-aliasing invariant true. New MxAccessGrpcMapperTests.MapCommandFromCommandClonesPayload (isolation + both overloads equal under a FakeTimeProvider). GWC-30: WorkerFrameReader reuses a per-instance _lengthPrefix scratch buffer instead of allocating 4 bytes per frame, with a class remark that ReadAsync is not reentrant (single read loop per WorkerClient; handshake reads complete before the loop starts); guarded by new WorkerFrameProtocolTests.ReadAsync_WithMultipleFramesOnOneReader_ParsesEveryFrame (5 frames, varying payload lengths, one reader). TST-28: new [Theory] WorkerClientTests.StartAsync_SendsGatewayHelloWithConfiguredMaxFrameBytes over the default and a 2 MiB override via FakeWorkerHarness.CreateConnectedPairAsync(maxMessageBytes:) — test-only, and the mutation check (hard-code MaxFrameBytes = 0) failed both cases before being reverted. Verification: NonWindows.slnx 0 warnings/0 errors; WorkerClientTests 25 passed, WorkerFrameProtocolTests 11 passed, MxAccessGrpcMapperTests 6 passed, MxAccessGatewayService* 29 passed, full gateway suite 844 passed / 0 failed (TMPDIR=/tmp on macOS).