mxaccessgw/docs/plans/2026-08-15-deferred-remediation.md

# Deferred-Findings Remediation Implementation Plan

> **For Claude:** REQUIRED SUB-SKILL: Use superpowers-extended-cc:subagent-driven-development to implement this plan task-by-task (Opus implementers per the user's instruction).

**Goal:** Resolve the six findings the 2026-08-15 perf-review remediation explicitly deferred (`docs/plans/2026-08-15-perf-review-remediation.md:611-620`) plus the pre-existing Windows-only `SecretsStorePathGuardTests` failure, so the deferred table empties and windev returns to a clean 1046/1046 gateway suite.

**Architecture:** Two phases. Phase A is gateway-side (net10, fully verifiable on macOS): the secrets-test fix, the distributor dictionary swap, event-path iterator flattening, and the dashboard in-process refactor that removes the Blazor pages' loopback SignalR hop while preserving the idle gate, mirror viewer gating, and clone-then-redact invariants. Phase B is worker-side (net48 x86, verified on windev over ssh): control-frame completion decoupling in the two-class frame writer, pipe-read teardown restructuring, and value-cache clone removal per the completed aliasing audit.

**Tech Stack:** .NET 10 / ASP.NET Core / Blazor Server / System.Threading.Channels (gateway); .NET Framework 4.8 x86 (worker); xUnit; windev CI clone `C:\build\mxaccessgw-ci` via `ssh windev`.

**Branch:** `perf/deferred-remediation` off local `main` (`15f188e`).

---

## Ground rules for every implementer subagent

- Shared working tree at `/Users/dohertj2/Desktop/MxAccessGateway`. **NEVER run `git stash`, `git reset`, `git clean`, `git checkout <sha/branch>`, or any command that touches files outside your task's `Files:` list.** Commit with explicit pathspecs only (`git add <your files> && git commit`).
- Build/test lock: before `dotnet build` or `dotnet test`, acquire the lock with `mkdir /private/tmp/claude-501/-Users-dohertj2-Desktop-MxAccessGateway/f36938ae-bbca-4245-b5c9-fac512d69e22/scratchpad/buildlock` (retry loop with sleep until it succeeds); `rmdir` it in ALL exit paths.
- `TreatWarningsAsErrors=true`, `Nullable=enable` repo-wide. Follow `docs/style-guides/CSharpStyleGuide.md`: file-scoped namespaces, `sealed` by default, `Async` suffix, MXAccess-aligned names.
- Worker projects (`ZB.MOM.WW.MxGateway.Worker*`) are net48/x86 and DO NOT COMPILE on macOS. For Phase B tasks: edit carefully, self-review for net48 compatibility (target-typed `new` and file-scoped namespaces ARE valid — `LangVersion=latest`; but no `Span`-based BCL overloads, no `IAsyncDisposable` on BCL types, `Channel` comes from System.Threading.Channels package which the worker already references). Compilation and tests happen at the Task 13 windev gate.
- Update affected docs in the same commit as the source (repo rule), except the dashboard design doc which Task 8 consolidates (deliberate, to avoid parallel edits to one file).
- MXAccess parity: never synthesize events, never mutate an event already handed to the outbound queue or wire.

---

## Phase A — gateway (macOS-verifiable)

### Task 1: Windows-safe cleanup in SecretsStorePathGuardTests

**Classification:** small
**Estimated implement time:** ~3 min
**Parallelizable with:** Task 2, Task 3, Task 4

**Files:**
- Modify: `src/ZB.MOM.WW.MxGateway.Tests/Configuration/SecretsStorePathGuardTests.cs`
- Modify: `docs/GatewayTesting.md` (lines ~557-565, the "fails deterministically on Windows" note)

**Why:** `CreateBuilder_AcceptsSecretsStoreOutsideContentRoot_AndCreatesIt` (lines 84-105) fails deterministically on Windows: `GatewayApplication.CreateBuilder` migrates the secrets store through `SecretsSqliteConnectionFactory` (`Pooling = true`, WAL), disposal returns the connection to the Microsoft.Data.Sqlite pool with the native handle open, and the `finally`'s `Directory.Delete(directory, recursive: true)` (line 103) hits a sharing violation. macOS passes only because Unix unlinks open files. The repo fixes this pattern twice already: `TestSupport/../TempDatabaseDirectory.cs:57` and `Configuration/PreHostSecretExpansionTests.cs:130-153`.

**Spec:**
1. In the failing test's `finally`, before `Directory.Delete`: call `Microsoft.Data.Sqlite.SqliteConnection.ClearAllPools();` and wrap the delete in `try { ... } catch (IOException) { } catch (UnauthorizedAccessException) { }` (best-effort, mirroring `TempDatabaseDirectory.Dispose`). Add a comment mirroring the one in `PreHostSecretExpansionTests.cs:133-137` (WAL + pooling keeps the handle alive past dispose).
2. Leave the rejection test alone (the guard means its file is never created).
3. Update `docs/GatewayTesting.md`: replace the "subtract it from the expected pass count on Windows" paragraph with a short note that the test's cleanup now clears the SQLite pool first and the failure is fixed as of this branch.

**Steps:** edit → `dotnet test src/ZB.MOM.WW.MxGateway.Tests/ZB.MOM.WW.MxGateway.Tests.csproj --filter "FullyQualifiedName~SecretsStorePathGuardTests"` (expect 2/2 on macOS; the real proof is the Task 13 windev gate) → commit `fix(tests): clear the SQLite pool before deleting the secrets path-guard temp dir — Windows sharing violation`.

---

### Task 2: SessionEventDistributor `_subscribers` → plain `Dictionary`

**Classification:** small
**Estimated implement time:** ~3 min
**Parallelizable with:** Task 1, Task 3, Task 4

**Files:**
- Modify: `src/ZB.MOM.WW.MxGateway.Server/Sessions/SessionEventDistributor.cs`

**Why:** All five access sites (`:365`, `:555`, `:771`, `:799`, `:813`) are inside `lock (_lifecycleLock)`; the lock-free hot path reads the copy-on-write `_subscriberSnapshot` array (`:958`, `:302`), never the dictionary. The concurrent type buys nothing. Audit confirmed no external/reflection access.

**Spec:** Change the field at `:107` to `Dictionary<long, Subscriber>`; `TryRemove(subscriber.Id, out _)` at `:799` becomes `Remove(subscriber.Id)`. Reword the type remarks at `:69-80`, `:111-123`, and `:298-300` where they name `ConcurrentDictionary` by design — the invariant to state is now: "the dictionary is only ever touched under `_lifecycleLock`; lock-free readers use `_subscriberSnapshot`."

**Steps:** edit → `dotnet test ... --filter "FullyQualifiedName~SessionEventDistributorTests"` (29 facts, expect all green) → commit `refactor(sessions): _subscribers to plain Dictionary — every access is under _lifecycleLock`.

---

### Task 3: Merge the session event-source pass-through iterator

**Classification:** standard
**Estimated implement time:** ~5 min
**Parallelizable with:** Task 1, Task 2, Task 4

**Files:**
- Modify: `src/ZB.MOM.WW.MxGateway.Server/Sessions/GatewaySession.cs` (`MapWorkerEventsAsync` ~:767-776, `ReadEventsAsync` ~:1517-1530)
- Test: `src/ZB.MOM.WW.MxGateway.Tests/Gateway/Sessions/GatewaySessionTests.cs` (existing)

**Why:** The worker→distributor source chain nests three compiler-generated async iterators per event: `WorkerClient.ReadEventsCoreAsync` → `GatewaySession.ReadEventsAsync` (pure pass-through: `TouchClientActivity(); yield return`) → `GatewaySession.MapWorkerEventsAsync` (`yield return mapper.MapEvent(...)`). The pass-through layer is two extra `MoveNextAsync` state-machine hops per event for no semantic value.

**Spec:**
1. FIRST grep all callers of `ReadEventsAsync`. If `MapWorkerEventsAsync` is its only caller, inline it: `MapWorkerEventsAsync` calls `GetReadyWorkerClientAsync`, iterates `client.ReadEventsAsync(ct)` directly, calls `TouchClientActivity()` per event, and `yield return mapper.MapEvent(workerEvent)`. Delete `ReadEventsAsync`. If other callers exist, keep the method for them but make `MapWorkerEventsAsync` self-contained as above — do NOT change any caller outside this file; report the finding.
2. Behavior must be byte-identical: same activity-touch cadence (per event), same exception propagation (WorkerClientException flows to the distributor pump unchanged), no event synthesis, worker order preserved.
3. `WorkerClient.ReadEventsCoreAsync`'s single-reader claim (`_eventsReaderClaimed`) must still be exercised exactly once per attach — do not add a second call site.

**Steps:** grep callers → edit → `dotnet test ... --filter "FullyQualifiedName~GatewaySession"` and `--filter "FullyQualifiedName~SessionEventDistributorTests"` → commit `perf(sessions): fold the ReadEventsAsync pass-through into MapWorkerEventsAsync — one fewer iterator per event`.

---

### Task 4: EventStreamService direct channel reads in the live loop

**Classification:** high-risk
**Estimated implement time:** ~5 min
**Parallelizable with:** Task 1, Task 2, Task 3

**Files:**
- Modify: `src/ZB.MOM.WW.MxGateway.Server/Grpc/EventStreamService.cs`
- Test: `src/ZB.MOM.WW.MxGateway.Tests/Gateway/Grpc/EventStreamServiceTests.cs` (existing 17 facts — must pass unchanged)

**Why:** The subscriber-side live loop materializes `subscriber.Reader.ReadAllAsync(ct).GetAsyncEnumerator(ct)` (`:109-111`) — a BCL async-iterator wrapper costing a state-machine hop per event on the hottest gateway path. Direct `ChannelReader` consumption (`WaitToReadAsync` + drain-with-`TryRead`) removes it.

**Spec:**
1. Replace the enumerator with direct reads: `while (await reader.WaitToReadAsync(ct)) { while (reader.TryRead(out MxEvent? mxEvent)) { ...existing per-event body... } }`; loop ends when `WaitToReadAsync` returns false (channel completed).
2. EVERY invariant in the current body survives, verbatim where possible:
   - ReplayGap sentinel emitted exactly once, first, only when `replayGap` (`:133-139`) — untouched, it precedes the live loop.
   - Replay batch stitching (`:141-150`) — untouched.
   - Per-RPC dedup watermark `if (mxEvent.WorkerSequence <= afterWorkerSequence) continue;` (`:179-182`) — must apply to every live event.
   - `WorkerClientException` catch → `session.MarkFaulted` → metrics → rethrow (`:164-174`): a completed-with-exception channel surfaces its exception from `WaitToReadAsync` — the catch must wrap the wait/read, preserving identical fault classification. Terminal `SessionManagerException(EventQueueOverflow)` propagates unchanged.
   - `finally` ordering (`:192-200`): with no enumerator to dispose, the remaining order is backlog-gauge registration disposal → lease disposal → `metrics.StreamDisconnected("Detached")`. Keep the comments explaining why.
3. Cancellation: `WaitToReadAsync(ct)` throws `OperationCanceledException` on detach — must reach the same code path the enumerator's cancellation did (the gRPC layer treats it as client disconnect). Verify against `StreamEventsAsync_WhenCanceled_DetachesSubscriber`.
4. No public-surface change; `MxAccessGatewayService` (`:151-179`) is untouched.

**Steps:** edit → run the full `EventStreamServiceTests` class + `GatewayEndToEndReconnectReplayTests` + `GatewayEndToEndMultiSubscriberTests` → commit `perf(grpc): consume the subscriber channel directly in StreamEventsAsync — drops the ReadAllAsync iterator hop`.

---

### Task 5: In-process dashboard snapshot feed + page switch

**Classification:** high-risk
**Estimated implement time:** ~8 min (accepted overage; splitting further would split one invariant)
**Parallelizable with:** Task 6, Task 7

**Files:**
- Create: `src/ZB.MOM.WW.MxGateway.Server/Dashboard/IDashboardSnapshotFeed.cs`
- Create: `src/ZB.MOM.WW.MxGateway.Server/Dashboard/DashboardSnapshotFeed.cs`
- Modify: `src/ZB.MOM.WW.MxGateway.Server/Dashboard/Components/DashboardPageBase.cs`
- Modify: `src/ZB.MOM.WW.MxGateway.Server/Dashboard/DashboardServiceCollectionExtensions.cs` (one `AddSingleton` line)
- Create: `src/ZB.MOM.WW.MxGateway.Tests/Gateway/Dashboard/DashboardSnapshotFeedTests.cs`

**Why:** Eight pages inherit `DashboardPageBase` and each opens a loopback `/hubs/snapshot` HubConnection (`DashboardPageBase.cs:62`) — a WebSocket round trip back into the same process per circuit. `IDashboardSnapshotService.WatchSnapshotsAsync` exists but is NOT multicast (each enumeration = its own `PeriodicTimer` + snapshot build), so pages must not call it directly; a shared feed does one enumeration and fans out.

**Spec:**
1. `IDashboardSnapshotFeed` (singleton): `IAsyncEnumerable<DashboardSnapshot> WatchAsync(CancellationToken ct)`. Internally: per-subscriber `Channel<DashboardSnapshot>` with capacity 1 and `BoundedChannelFullMode.DropOldest` (a dashboard viewer only ever wants the latest snapshot; a slow circuit must never buffer unboundedly or stall others).
2. **Idle gating (the invariant this task must not lose):** the feed enumerates `IDashboardSnapshotService.WatchSnapshotsAsync` on a background task started when the subscriber count goes 0→1 and cancelled when it goes 1→0. While zero subscribers, the feed holds no timer and builds no snapshot. Guard subscriber add/remove with a plain lock; restart cleanly on resubscribe (mirror the start/stop discipline of `GatewayAlarmMonitor.StreamAsync` registration, `GatewayAlarmMonitor.cs:739-752`). If the underlying watch throws or completes, complete all subscriber channels with the error and reset so the next subscriber restarts it (mirror `DashboardSnapshotPublisher.ExecuteAsync`'s reconnect-after-delay posture, but per-feed).
3. `DashboardPageBase`: remove the HubConnection path (`:62` and the factory usage); keep the synchronous first render via `snapshotService.GetSnapshot()` (`:37`); then a background loop `await foreach (var s in feed.WatchAsync(_cts.Token)) { Snapshot = s; await InvokeAsync(StateHasChanged); }` started in `OnAfterRenderAsync(firstRender)` or `OnInitializedAsync` (match current lifecycle), cancelled + awaited in `DisposeAsync`. Update the class XML doc that narrates the hub subscription history (`:7-14`).
4. Hubs, `DashboardSnapshotPublisher`, `DashboardSnapshotHubConnectionCounter`, `DashboardHubConnectionFactory`, and `/hubs/token` all stay — they remain the remote/external surface. Do not touch them. *(As-built deviation, integration-fix commit: once the pages stopped using it, `DashboardHubConnectionFactory` had zero consumers, so the final integration review had it deleted along with the `Microsoft.AspNetCore.SignalR.Client` package reference. Hubs, publisher, counter, and `/hubs/token` remain the remote surface as specified.)*
5. Auth: the pages are mapped behind `ViewerPolicy` (`DashboardEndpointRouteBuilderExtensions.cs:136`), which remains the gate for in-process consumption; add one comment on `WatchAsync` saying so.
6. Tests (`DashboardSnapshotFeedTests`): (a) zero subscribers → underlying service's `WatchSnapshotsAsync` never enumerated (fake service counts enumerations/`MoveNextAsync`); (b) first subscriber starts exactly one enumeration; two subscribers share it; (c) last unsubscribe cancels it; resubscribe restarts it; (d) slow subscriber observes latest-wins (push 3 snapshots, read 1, it is the newest) while a fast subscriber sees all; (e) underlying fault completes subscribers with the error and a fresh subscriber restarts.

**Steps:** write feed tests first (fail) → implement feed → page switch → `dotnet test ... --filter "FullyQualifiedName~DashboardSnapshotFeed"` then `--filter "FullyQualifiedName~Dashboard"` (whole dashboard test folder) → commit `feat(dashboard): in-process snapshot feed replaces the pages' loopback /hubs/snapshot hop`.

---

### Task 6: In-process session event subscription + SessionDetailsPage switch

**Classification:** high-risk
**Estimated implement time:** ~8 min
**Parallelizable with:** Task 5, Task 7

**Files:**
- Modify: `src/ZB.MOM.WW.MxGateway.Server/Dashboard/Hubs/DashboardEventBroadcaster.cs`
- Modify: `src/ZB.MOM.WW.MxGateway.Server/Dashboard/Hubs/EventsHubViewerRegistry.cs` (only if a member is needed for synthetic connection ids; prefer reusing the existing API)
- Modify: `src/ZB.MOM.WW.MxGateway.Server/Dashboard/Components/Pages/SessionDetailsPage.razor` (the `/hubs/events` connection at `:271,297`)
- Test: `src/ZB.MOM.WW.MxGateway.Tests/Gateway/Dashboard/DashboardEventBroadcasterTests.cs` (extend)

**Why:** `SessionDetailsPage` opens a loopback `/hubs/events` connection. The broadcaster already short-circuits on `!viewerRegistry.HasViewers(sessionId)` BEFORE the redaction deep clone (`DashboardEventBroadcaster.cs:51-56`) — the mirror viewer gating shipped last round. An in-process subscription must keep feeding that registry or every unwatched session pays `MxEvent.Clone()` per event again.

**Spec:**
1. Add to `DashboardEventBroadcaster` an in-process subscribe API: `IDashboardEventSubscription Subscribe(string sessionId)` returning a disposable that exposes `ChannelReader<MxEvent> Reader` (bounded, capacity ~256, `DropOldest` — this is a UI mirror, loss is acceptable and already documented for the hub path). On subscribe: register a synthetic connection id (e.g. `"inproc-" + Guid.NewGuid().ToString("N")`) with `EventsHubViewerRegistry.AddViewer(connectionId, sessionId)`; on dispose: `RemoveViewer` + `ReleaseConnection` in the order the hub uses (`EventsHub.cs:86,99`). Registry stays the single source of truth for `HasViewers`.
2. `Publish` (`:39-86`): after the existing `HasViewers` check and the clone-then-redact (`RedactValues` `:97-109`), `TryWrite` the SAME redacted clone to each in-process subscriber of that session, in addition to the hub group send. The source `MxEvent` is shared with the gRPC stream and replay ring — the existing never-mutate-in-place rule holds; in-process subscribers receive the redacted clone only.
3. `SessionDetailsPage`: replace the HubConnection + `SubscribeSession` invoke with `broadcaster.Subscribe(SessionId)` and a read loop marshalling to the renderer via `InvokeAsync(StateHasChanged)`; dispose the subscription in `DisposeAsync`. Keep the existing per-session ACL posture (any Viewer may watch any session — SEC-25 is tracked separately; do not widen or narrow it here).
4. Tests to add in `DashboardEventBroadcasterTests`: (a) in-process subscriber receives the redacted event when `ShowTagValues=false` and the source event is not mutated; (b) subscribing flips `HasViewers` so `Publish` stops short-circuiting (proves mirror gating integration); (c) disposing the last in-process subscriber restores the no-viewers short-circuit (no clone, no send — reuse the existing `Publish_WithNoRegisteredViewers_DoesNotCloneOrSend` fake pattern); (d) hub viewers and in-process viewers are independently counted.

**Steps:** tests first → implement → `dotnet test ... --filter "FullyQualifiedName~DashboardEventBroadcaster"` + `--filter "FullyQualifiedName~EventsHubViewerRegistry"` + `--filter "FullyQualifiedName~GatewaySessionDashboardMirror"` → commit `feat(dashboard): in-process session event subscription feeds the viewer registry — SessionDetailsPage drops its /hubs/events hop`.

---

### Task 7: AlarmsPage provider-status via IGatewayAlarmService

**Classification:** standard
**Estimated implement time:** ~4 min
**Parallelizable with:** Task 5, Task 6

**Files:**
- Modify: `src/ZB.MOM.WW.MxGateway.Server/Dashboard/Components/Pages/AlarmsPage.razor` (`:194` HubConnection, `:281-304` poll loop untouched)

**Why:** `AlarmsPage` opens `/hubs/alarms` but only consumes `ProviderStatus` payloads from it (alarm rows come from the 3 s `QueryAlarmsAsync` poll). `IGatewayAlarmService.StreamAsync` (`GatewayAlarmMonitor.cs:724-777`) is already a true multi-subscriber in-process fan-out.

**Spec:** Replace the HubConnection with a background loop over `alarmService.StreamAsync(alarmFilterPrefix: null, ct)`, handling only `PayloadOneofCase.ProviderStatus` (skip snapshot/live alarm payloads — the poll stays authoritative for rows). The monitor's drop policy completes a lagging subscriber's channel (`:700-712`): on completion or fault, delay ~1 s and resubscribe (matching the hub path's `WithAutomaticReconnect` posture). Dispose via the page's existing cancellation. Leave the poll loop alone.

**Steps:** edit → `dotnet build src/ZB.MOM.WW.MxGateway.Server` → `dotnet test ... --filter "FullyQualifiedName~Alarms"` → commit `feat(dashboard): AlarmsPage reads provider status from IGatewayAlarmService in-process`.

---

### Task 8: Dashboard design-doc update (consolidated)

**Classification:** small
**Estimated implement time:** ~4 min
**Parallelizable with:** none (runs after 5, 6, 7 land)

**Files:**
- Modify: `docs/GatewayDashboardDesign.md` (sections at ~:112-114, :162-178, :190-217, :228-247, :535-541, :581-595)

**Spec:** Rewrite the affected sections to describe: pages consume in-process seams (`IDashboardSnapshotFeed`, `DashboardEventBroadcaster.Subscribe`, `IGatewayAlarmService.StreamAsync`); the three hubs and `/hubs/token` remain as the remote/external surface; idle gating is now two-tier (hub connection counter gates the hub publisher; feed subscriber count gates the in-process pump — while nobody watches, neither builds a snapshot); mirror gating counts hub viewers AND in-process viewers through the one registry; clone-then-redact still happens once in the broadcaster before any delivery; ViewerPolicy on the component endpoint is the in-process auth gate; SEC-25 per-session ACL gap unchanged. Present tense, why-not-what, no marketing.

**Commit:** `docs(dashboard): in-process page feeds, two-tier idle gating, hubs as the external surface`

---

### Task 9: Phase A gate — full gateway suite on macOS

**Classification:** trivial (verification only)
**Parallelizable with:** none (after Tasks 1-8)

Run `dotnet build src/ZB.MOM.WW.MxGateway.NonWindows.slnx` (expect 0 warnings) and the full `dotnet test src/ZB.MOM.WW.MxGateway.Tests/ZB.MOM.WW.MxGateway.Tests.csproj` (expect ≥1046 passed, 0 failed; new feed/broadcaster tests raise the count). Fix-forward any failure before Phase B.

---

## Phase B — worker (net48 x86, verified on windev)

### Task 10: Control-frame completion decoupling in WorkerFrameWriter

**Classification:** high-risk
**Estimated implement time:** ~6 min
**Parallelizable with:** Task 11, Task 12

**Files:**
- Modify: `src/ZB.MOM.WW.MxGateway.Worker/Ipc/WorkerFrameWriter.cs`
- Modify: `src/ZB.MOM.WW.MxGateway.Worker.Tests/Ipc/WorkerFrameProtocolTests.cs`
- Modify: `docs/WorkerFrameProtocol.md` (~:120-131 completion-semantics paragraph)

**Why:** Wire ordering is already correct — `DequeueNext` (`:383-413`) re-checks `_controlFrames` before every frame. The coupling is completion latency: `DrainQueuedFramesAsync` (`:304-361`) defers the single `FlushAsync` and ALL `TrySetResult` calls to after the whole drain pass, so a heartbeat/command-reply/fault/shutdown-ack `Task` awaited by its writer does not resolve until up to 128 event frames behind it are written and flushed. The XML docs claim "never delayed behind an event backlog" — true of bytes, false of the awaited completion.

**Spec:**
1. Record the priority class on `PendingFrame` (`:23-48`), set at construction in `WriteAsync` (`:109`) and `WriteBatchAsync` (`:192`).
2. In `DrainQueuedFramesAsync`: when `DequeueNext` returns an `Event` frame while `written` contains one or more not-yet-completed `Control` frames, first `FlushAsync` + complete + clear `written`, then continue draining. Exit-path flush at `:339-360` unchanged. Net effect: a control frame's completion never waits on an event frame dequeued after it; the pure-event 128-batch hot path still pays exactly one flush (guarded by the existing `WriteAsync_WhenBatchDrainedTogether_FlushesOnce` and `EventBurst_DrainLoopCoalescesFlushes`); a pure-control burst still pays one flush. Do NOT flush per control frame unconditionally — that reintroduces the pre-WRK-12 syscall-per-heartbeat cost.
3. Failure handling: `FailFrames(written, ...)` / `FailAllQueued` (`:327-336`) operate on the current `written` list; after an early flush+complete+clear, frames already completed must not be failable — verify the clear ordering makes that structurally true, and extend the fault-injection tests if the early-flush path adds a new failure window (a `FlushAsync` fault with a partially-completed pass).
4. New test (use the existing `GatedWriteStream` harness ~`:880`): queue a control frame behind N gated event frames within one drain pass; assert the control frame's `WriteAsync` task completes before the last event write is released. Keep all 9 existing writer tests green — sequence stamping (`:431-483`), claim/tombstone interlock (`:244-274`), and wire order must be untouched.
5. `docs/WorkerFrameProtocol.md`: update the completion-semantics paragraph — completion now resolves at the class-transition flush, still meaning "written AND flushed".

**Commit:** `perf(worker): control-frame completions resolve at the class-transition flush, not after the event batch`

---

### Task 11: Worker pipe-read teardown — dispose-to-unblock and observe the abandoned read

**Classification:** high-risk
**Estimated implement time:** ~8 min
**Parallelizable with:** Task 10, Task 12

**Files:**
- Modify: `src/ZB.MOM.WW.MxGateway.Worker/Ipc/WorkerPipeSession.cs` (`RunMessageLoopAsync` `:267-310`, ctor `:55-68`)
- Modify: `src/ZB.MOM.WW.MxGateway.Worker/Ipc/WorkerPipeClient.cs` (`:143-159`) — only if ownership must move; prefer not
- Modify: `src/ZB.MOM.WW.MxGateway.Worker.Tests/Ipc/WorkerPipeSessionTests.cs`
- Modify: `src/ZB.MOM.WW.MxGateway.Worker/Ipc/WorkerFrameReader.cs` (comment only)

**Why:** On net48, `NamedPipeClientStream.ReadAsync` ignores its `CancellationToken` (`WorkerFrameReader.cs:109-111`). Fault-path exits (event-drain fault, oversized event, watchdog, heartbeat write failure) leave `readTask` pending; it is unblocked only when `WorkerPipeClient`'s `using` disposes the pipe, at which point it faults with `ObjectDisposedException`/`IOException` on a Task nobody observes (the finally at `:303-309` awaits only heartbeat and drain). The frame-pooling change (GWC-30) makes this sharper: the abandoned read owns the per-instance `_lengthPrefix` buffer and possibly a rented ArrayPool payload — the reader's single-consumer invariant holds today only because nothing ever reads again after abandonment.

**Spec — constraints, implementer designs within them:**
1. **No unobserved faulted Task.** After the stream is disposed, `readTask`'s fault must be awaited/observed (reuse `ObserveBackgroundTaskStopAsync`'s timeout-and-log shape, `:312-348`) before `WorkerPipeClient.RunAsync` returns.
2. **Ordering: final writes complete before disposal.** The shutdown ack (`WriteShutdownAckAsync` `:1064-1069`) and fault frames (`TryWriteFaultAsync` `:1164+`) are written after the message loop exits on some paths — trace every exit path and place the stream disposal AFTER the last possible write on each. The clean design: `WorkerPipeSession` keeps a reference to the ctor `Stream`; `RunAsync`'s outermost finally (after runtime-session disposal and any fault write, `:133-145`) disposes the stream and then observes `readTask` (stored in a field by `RunMessageLoopAsync`). `WorkerPipeClient`'s `using` then double-disposes harmlessly. If the trace shows a fault write that happens in `WorkerPipeClient` after `session.RunAsync` returns (there is none known), fall back to moving observation into `WorkerPipeClient`.
3. **Never a second read.** After abandonment, no code path may call `_reader.ReadAsync` again (pooled-buffer use-after-return). The message loop already guarantees this (`return` before reassignment on the graceful path); keep it structurally true and assert it in a comment on `_lengthPrefix` (`WorkerFrameReader.cs:23-25`).
4. **Graceful path unchanged:** `WorkerShutdown`/`ShutdownWorker` exits have no pending read; disposal+observation must be a no-op there (observe a completed/absent task).
5. Document the net48 token-ignoring fact where the read is issued (`RunMessageLoopAsync` and/or `ReadExactlyOrThrowAsync`) — the research found zero comments acknowledging it.
6. Tests (net48 project, real `PipePair` harness `:2433-2485`): (a) fault-path exit (reuse the `RunAsync_EventFrameTooLarge_...` shape `:868`) — assert `RunAsync` completes within the existing 5 s bound AND, via a `TaskScheduler.UnobservedTaskException` hook armed in the test with a forced GC, that no unobserved exception leaks; (b) graceful shutdown still completes with no pending read; (c) the session disposes the stream (harness observes the gateway-side stream faulting its own pending read promptly rather than at `PipePair.Dispose`).

**Commit:** `fix(worker): session-owned stream disposal unblocks and observes the net48 pipe read at teardown`

---

### Task 12: Value-cache clone removal per the aliasing audit

**Classification:** standard
**Estimated implement time:** ~5 min
**Parallelizable with:** Task 10, Task 11

**Files:**
- Modify: `src/ZB.MOM.WW.MxGateway.Worker/MxAccess/MxAccessValueCache.cs` (`Set` `:82,83,97`; `CachedValue` `:275`)
- Modify: `src/ZB.MOM.WW.MxGateway.Worker.Tests/MxAccess/MxAccessValueCacheTests.cs` (rewrite the `:58` test)
- Modify: `src/ZB.MOM.WW.MxGateway.Worker.Tests/MxAccess/MxAccessCommandExecutorTests.cs` (add cached-read test)

**Why (audit result):** All three clones in `Set` — `Value.Clone()` (deep, recursive for arrays), `SourceTimestamp.Clone()`, `Statuses.Clone()` (container + N proxies) — are removable. The event is fully stamped BEFORE `Set` runs (`Enqueue` at `MxAccessBaseEventSink.cs:263` precedes `postPublish` at `:288`; sequence/timestamp stamped inside `Enqueue`, `MxAccessEventQueue.cs:269-270`) and the queue's ownership invariant forbids later mutation. The alias already exists on the read side: `SucceededRead` (`MxAccessSession.cs:1086,1091,1096`) hands the cache's own `Value`/`SourceTimestamp` instances into every `BulkReadResult`, which downstream only wraps and serializes. Worker↔gateway is a process boundary — no gateway consumer can alias.

**Spec:**
1. Remove all three clones; `CachedValue` stores the event's own references.
2. Ownership contract comment on `Set` and on `CachedValue`: the cache holds borrowed references into an enqueued, write-once `MxEvent`; consumers may read and serialize, never mutate; mutation would additionally invalidate `QueuedEvent.Size` — the enqueue-time memoized serialized size that the byte-budgeted `Drain` charges (`MxAccessEventQueue.cs:499-506`), so a grown message could overshoot the negotiated frame max and fault the session via `MessageTooLarge`.
3. Rewrite `Set_StoresIndependentSnapshot_UnaffectedByLaterEventMutation` (`:58` — it codifies the invariant being reversed) into the aliasing contract: `Set` then `TryGet` returns the same `Value`/`SourceTimestamp`/`Statuses`-element instances (`Assert.Same`), with the doc comment explaining the write-once borrow.
4. Add the missing cached-read-path test in `MxAccessCommandExecutorTests`: seed the cache, dispatch a `ReadBulk` that hits `TryGetCachedReadFor` → assert `WasCached == true` and `result.Value` is reference-equal to the cached instance (closing the coverage gap the audit found — nothing today exercises `WasCached == true` end-to-end in the worker).
5. `MxAccessWriteCompletionCache.Record`'s parallel `statuses.Clone()` (`:76`) is left AS-IS deliberately (different lifecycle, not in the finding) — add one cross-reference comment there pointing at the value-cache ownership contract.

**Commit:** `perf(worker): value cache borrows the write-once event's instances — three clones per OnDataChange removed`

---

### Task 13: Phase B gate — windev full verification

**Classification:** trivial (verification only)
**Parallelizable with:** none (after Tasks 10-12; Phase A gate must be green)

Push the branch to origin, then on windev (`ssh windev`, clone `C:\build\mxaccessgw-ci`): fetch + checkout the branch; `dotnet build src/ZB.MOM.WW.MxGateway.slnx` (0 warnings); `dotnet build src/ZB.MOM.WW.MxGateway.Worker/... -p:Platform=x86`; `dotnet test src/ZB.MOM.WW.MxGateway.Worker.Tests/... -p:Platform=x86` (expect 501+ passed, 0 failed — new tests raise the count); `dotnet test src/ZB.MOM.WW.MxGateway.Tests/...` (expect **0 failed including SecretsStorePathGuardTests** — the Task 1 proof). Known caveat: the reconnect-replay test is load-sensitive on windev; re-run isolated before treating it as a regression (documented in `docs/GatewayTesting.md`).

---

### Task 14: Wrap-up — deferred table closure, docs sweep, final review

**Classification:** small
**Parallelizable with:** none (last)

- Append a closure note to `docs/plans/2026-08-15-perf-review-remediation.md`'s deferred table (one line: resolved by this plan, date, branch).
- Sweep: `gateway.md` / `docs/WorkerFrameProtocol.md` / `docs/GatewayDashboardDesign.md` / `docs/GatewayTesting.md` consistency with as-built behavior; record any accepted deviations in THIS plan's "As-built notes" section (add it).
- Update `.tasks.json` statuses; update auto-memory (`perf-remediation-branch.md` or successor) with the branch state.
- Dispatch the final integration code review (Opus) over `git diff main..perf/deferred-remediation` before reporting done. Merge remains the user's decision.

---

## Explicitly out of scope

| Item | Why |
|---|---|
| wnwrap alarm GUID identity semantics; `ALARM_RECORDS/@COUNT` probe | Need live alarms on windev — external state this plan cannot provide. Still tracked in the prior plan's follow-ups. |
| Structural alarm-truncation degraded-status signal | Contract-level design (proto change candidate) — separate effort. |
| SEC-25 per-session dashboard event ACL | Security roadmap item; Task 6 deliberately preserves the current posture. |
| `MxAccessWriteCompletionCache` clone | Different lifecycle than the value cache; consciously kept (Task 12.5). |

---

## As-built notes (execution record)

Where the delivered work differs from the task text above, or where the route to it
is worth keeping, this is the record.

**Task 3 — `ReadEventsAsync` retained.** The method was not removed after
`MapWorkerEventsAsync` inlined the read-then-map chain: a second caller reaches it
through `ISessionManager.ReadEventsAsync`. That interface member itself has zero
production call sites — only test fakes implement and exercise it. Deleting it is a
mechanical but wide change (~15 test-fake touches), so it is recorded as a follow-up
rather than done here. Removed by `docs/plans/2026-08-17-deferred-closeout.md` Task 1,
2026-08-17.

**Task 5 — dashboard event feed, two review rounds.** Review caught two races that
the first cut did not have. First, subscription lifetime: subscriptions are now
generation-tagged, a generation ends at the time the fault is *observed* (not when it
is raised), `Reset` is scoped to the dying generation so it cannot cancel its
successor, and a backstop restart covers the case where no subscriber is left to
drive recovery. Second, `UnsubscribeAsync` needed a generation-scoped idle gate so a
teardown for an old generation cannot tear down the new one. Both fixes are pinned by
tests verified against mutations of the fixed code.

**Task 6 — subscribe API placement.** The subscribe surface lives on
`IDashboardSessionEventSubscriber`, with DI forwarding to a single instance so every
consumer shares one feed. Batches that arrive for a session the renderer has already
moved off are dropped by a subscription identity check inside the renderer dispatch,
which is what makes a stale batch harmless rather than a cross-session leak.

**Task 10 — the delivered property is the delivery point, not awaited latency.** The
spec asked for control-frame completion to be observable before the pass's event
writes. That is unachievable in the enqueue-then-contend shape: a caller that loses
the write-lock race does not run again until the winning drainer releases the lock,
so its `await` cannot return early no matter when its frame completes. What shipped
is the honest half: control frames are written *and flushed* at the class-transition
boundary, so the priority class governs the frame's delivery point rather than only
its byte order. Getting the awaited-latency win too requires unparking the lock-race
loser from the winner's pass — a change to the write-lock shape, recorded as a
follow-up. One extra `FlushFileBuffers` per mixed pass is the accepted cost.
That lock-parking was closed by `docs/plans/2026-08-17-deferred-closeout.md`
Task 2, 2026-08-17: `WriteAsync` races its own frame's completion against the
lock acquisition and detaches the wait it abandons.

**Task 11 — teardown ordering and unconditional fault observation.** Teardown disposes
the session-owned transport first, then observes the read that dispose abandoned.
Fault observation is unconditional — a `ContinueWith(..., TaskContinuationOptions.OnlyOnFaulted)`
continuation, so the budget that bounds the wait is diagnostics-only and can never be
the reason a fault goes unobserved. The same continuation covers heartbeat and drain
overrun. `DisposeTransportStream` is exception-total: no dispose path can throw out of
teardown.

**Task 12 — three clones removed, plan rationale corrected in-code.** All three
`OnDataChange` value-cache clones are gone. The plan's stated reason for keeping the
`MxAccessWriteCompletionCache` clone ("different lifecycle than the value cache") is
wrong and was corrected where the code documents it: the clone is kept on
*provenance* grounds — the cached payload comes from a caller-supplied object the
worker does not own — not on lifecycle grounds.

**Task 13 — windev verification.** Solution build 0 warnings / 0 errors after
clearing stale `Contracts` `obj` artifacts (an infrastructure problem on the box, not
a regression from this branch). Worker x86: 509/509 (+8 new). Gateway: 1059/1059,
including `SecretsStorePathGuardTests` — the first fully green Windows gateway run,
that suite having been red before this branch. One load flake
(`InvokeAsync_WhenWorkerHandshakingThenReadyWithinTimeout_Succeeds`) passed in
isolation and on re-run, consistent with the load-sensitivity caveat documented in
`docs/GatewayTesting.md`.