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+# Plan: Aggregated Live Alarm Stream for Alarm Summary (deferred #10)
+
+**Status:** Draft plan (not yet executed) — 2026-07-10
+**Register row:** `docs/plans/2026-07-08-deferred-work-register.md` #10
+**Revisit trigger that fired this plan:** *"Alarm Summary latency complaints or >~50 instances/site."*
+**Owning component:** Central UI (#9) + Central–Site Communication (#5); no new component.
+
+---
+
+## 1. Problem
+
+The operator Alarm Summary page (`/monitoring/alarms`, `RequireDeployment`, read-only)
+currently rebuilds its whole view every 15 s by fanning out a per-instance
+`DebugViewSnapshot` Ask to **every Enabled instance on the selected site** and
+aggregating client-side (`AlarmSummaryService`, `MaxConcurrentFetches = 8`). At
+current instance counts this is acceptable; past **~50 instances/site** the poll
+does 50 cross-cluster Asks every 15 s (worst case 50 × ClusterClient round-trips
+gated 8-at-a-time), so freshness degrades and the active central node carries a
+periodic burst. We want an **aggregated live feed** so the page reflects alarm
+transitions in near-real-time without re-polling the whole site.
+
+## 2. Hard constraint (locked decision — do not violate)
+
+`docs/plans/2026-05-29-native-alarms-design.md:24` marks **"no central alarm
+tables, no central history"** as `[PERM]`. Therefore this plan introduces **no
+persisted central alarm store** — only a **transient in-memory per-site live
+cache** on the active central node, seeded from the existing snapshot fan-out and
+kept warm by a live gRPC delta stream. If a persisted store is ever wanted, that
+is a separate re-decision, not part of this plan.
+
+## 3. Chosen approach
+
+**A shared, reference-counted, per-site central live alarm cache**, seeded by the
+existing snapshot fan-out and updated by a new **site-wide, alarm-only** gRPC
+stream, pushed to the Blazor page via an in-process singleton event (the
+`IDeploymentStatusNotifier` pattern — no new SignalR hub; the Blazor circuit
+already pushes).
+
+### Why site-wide RPC (Option B) over N per-instance streams (Option A)
+
+The revisit trigger is *>~50 instances/site* — exactly where opening one gRPC
+stream per instance (Option A) strains `GrpcMaxConcurrentStreams = 100` and
+duplicates the fan-out problem in streaming form. A single **`SubscribeSite`**
+stream per site (alarm events only; attributes are far higher-volume and the
+summary never shows them) is the scalable answer and is an *additive* proto
+change. It reuses the existing `SiteStreamManager` broadcast hub by adding a
+subscribe variant that drops the per-instance `InstanceUniqueName` filter
+(`SiteStreamManager.cs:101`) and keeps only `AlarmStateChanged` events.
+
+### Lifecycle & failover
+
+- **Shared per-site cache**, reference-counted by active viewers: first viewer of
+  a site starts the subscription + snapshot seed; last viewer leaving stops it
+  (with a short linger to avoid thrash). One gRPC stream per *site*, not per
+  browser circuit.
+- **Seed-then-stream** ordering copied from `DebugStreamBridgeActor`: open the
+  stream first, buffer live deltas, run the snapshot fan-out once, flush buffer
+  with dedup, then live pass-through. Dedup identity = `(InstanceUniqueName,
+  AlarmName, SourceReference)` (matches `DebugStreamBridgeActor.AlarmKey`).
+- **NodeA↔NodeB reconnect** with retry budget + stability window, reusing the
+  reconnect logic already proven in `DebugStreamBridgeActor`.
+- **Placeholder reconciliation:** live stream drops `IsConfiguredPlaceholder`
+  rows (`StreamRelayActor.cs:63`); snapshots include them. Cache seeds
+  placeholders from the snapshot and never expects them on the live stream.
+- **Instance-set drift:** on deploy/enable/disable/delete the site-wide stream
+  naturally starts/stops carrying that instance's events; a periodic (e.g. 60 s)
+  reconcile snapshot corrects any missed enable/disable so the cache can't drift
+  indefinitely. This replaces the old "re-query everything every 15 s" with
+  "stream + occasional reconcile."
+
+## 4. Task breakdown
+
+Classification legend: `trivial` / `small` (code review) / `standard` (spec+code
+review) / `high-risk` (serial reviews + integration). Times are single-task
+estimates.
+
+### Task 1 — Site-wide alarm-only stream on the site runtime `[standard]`
+- **Files:** `src/ZB.MOM.WW.ScadaBridge.SiteRuntime/Streaming/SiteStreamManager.cs`
+- Add `SubscribeSiteAlarms(ISiteStreamSubscriber subscriber)` — same broadcast-hub
+  wiring as `Subscribe(...)` but **without** the `InstanceUniqueName` filter and
+  **filtering to `AlarmStateChanged` only** (skip `AttributeValueChanged`).
+- Return an `IDisposable`/kill-switch symmetric with the existing per-instance
+  subscribe. Unit-test that alarm events for *all* instances arrive and attribute
+  events do not.
+
+### Task 2 — `SubscribeSite` gRPC contract + server handler `[standard]`
+- **Files:** `src/ZB.MOM.WW.ScadaBridge.Communication/Protos/sitestream.proto`,
+  `src/ZB.MOM.WW.ScadaBridge.Communication/Grpc/SiteStreamGrpcServer.cs`,
+  `src/ZB.MOM.WW.ScadaBridge.Communication/Actors/StreamRelayActor.cs`
+- Add **additive** `rpc SubscribeSite(SiteStreamRequest) returns (stream
+  SiteStreamEvent)` + `SiteStreamRequest { correlation_id }` (no instance name).
+  Keep `bundleFormatVersion`/message numbering additive — do not renumber
+  existing fields.
+- Server handler mirrors `SubscribeInstance` (bounded `Channel(1000,
+  DropOldest)`, `GrpcMaxConcurrentStreams`/`GrpcMaxStreamLifetime` limits, the
+  `StreamRelayActor` mapping, `SiteConnectionOpened/Closed` telemetry) but calls
+  `SubscribeSiteAlarms`. `StreamRelayActor` already drops placeholder rows and
+  emits enriched `AlarmStateUpdate` — reuse unchanged.
+
+### Task 3 — Central per-site subscription client `[standard]`
+- **Files:** `src/ZB.MOM.WW.ScadaBridge.Communication/Grpc/SiteStreamGrpcClient.cs`,
+  `.../Grpc/SiteStreamGrpcClientFactory.cs`
+- Add `SubscribeSiteAsync(correlationId, onAlarmEvent, onError, ct)` alongside
+  `SubscribeAsync`, reusing `ConvertToDomainEvent` (maps proto → domain
+  `AlarmStateChanged`). Factory already caches channels per `(site, endpoint)` for
+  failover — no change needed beyond the new call.
+
+### Task 4 — Central live alarm cache actor/service `[high-risk]`
+- **Files (new):** `src/ZB.MOM.WW.ScadaBridge.Communication/Actors/SiteAlarmAggregatorActor.cs`,
+  `src/ZB.MOM.WW.ScadaBridge.Communication/SiteAlarmLiveCacheService.cs`,
+  `src/ZB.MOM.WW.ScadaBridge.Communication/ISiteAlarmLiveCache.cs`
+- **Files (edit):** `src/ZB.MOM.WW.ScadaBridge.Communication/ServiceCollectionExtensions.cs`
+- Per-site aggregator: seed-then-stream (buffer → snapshot fan-out via existing
+  `CommunicationService.RequestDebugSnapshotAsync` → flush+dedup → live), holds a
+  `Dictionary<AlarmKey, AlarmStateChanged>` snapshot of current alarm state.
+  Reference-counted start/stop keyed by site. NodeA↔NodeB reconnect + periodic
+  reconcile snapshot (60 s). Reuse `DebugStreamBridgeActor` reconnect logic
+  (extract shared helper or copy with attribution).
+- Expose `ISiteAlarmLiveCache` (singleton) with `Subscribe(siteId, onChange)` →
+  `IDisposable`, raising an `IDeploymentStatusNotifier`-style event on each
+  applied delta. This is the **highest-risk** task (concurrency, failover,
+  seed/stream ordering) — spawn a code-reviewer subagent and add integration
+  coverage.
+
+### Task 5 — Wire Alarm Summary page to the live cache `[standard]`
+- **Files:** `src/ZB.MOM.WW.ScadaBridge.CentralUI/Services/AlarmSummaryService.cs`,
+  `.../Services/IAlarmSummaryService.cs`,
+  `.../Components/Pages/Monitoring/AlarmSummary.razor`,
+  `.../ServiceCollectionExtensions.cs`
+- Add `SubscribeSiteAlarmsAsync(siteId, onChange)` to the service, delegating to
+  `ISiteAlarmLiveCache`. Page: on site select, subscribe; `onChange` updates
+  `_rows` + recomputes `_rollup`/`_visibleRows` and `StateHasChanged()` (over the
+  Blazor circuit). **Keep the 15 s poll as a fallback** but gate it behind a
+  feature flag / degrade path when the live cache is healthy, so a stream failure
+  never blanks the page. Unsubscribe in `Dispose()`. `AlarmStateBadges` and all
+  client-side filters/sort are unchanged (they already consume `AlarmStateChanged`).
+
+### Task 6 — Options, limits, and telemetry `[small]`
+- **Files:** communication options class (grep `CommunicationOptions` /
+  `GrpcMaxConcurrentStreams`), `SiteAlarmLiveCacheService`
+- Add options: live-cache linger, reconcile interval, per-site subscriber cap.
+  Validate (eager options validation is the house rule). Surface a gauge for
+  active per-site aggregators + reconnect count on the health snapshot, mirroring
+  `SiteConnectionUp` gauges.
+
+### Task 7 — Tests + integration trace `[standard]`
+- **Files:** `tests/.../Communication.Tests/*`, `tests/.../CentralUI.Tests/*`,
+  `tests/.../SiteRuntime.Tests/Streaming/SiteStreamManagerTests.cs`
+- Unit: `SubscribeSiteAlarms` filtering; `SubscribeSite` server/client mapping;
+  aggregator seed/stream/dedup/placeholder/reconnect; page subscribe/unsubscribe.
+- Integration: end-to-end site→central alarm delta reaches the cache; failover
+  flip re-seeds; last-viewer stop tears the stream down. Live-smoke on the docker
+  cluster (`bash docker/deploy.sh`) with >1 instance raising alarms.
+
+### Task 8 — Docs `[trivial]`
+- **Files:** `docs/requirements/Component-CentralUI.md` (Alarm Summary section —
+  replace "no aggregated live stream" with the shipped design),
+  `docs/requirements/Component-Communication.md` (new `SubscribeSite` RPC),
+  `docs/plans/2026-06-18-m7-opcua-mxgateway-ux-design.md` (mark T13 follow-up
+  delivered), and move register #10 to **Resolved**.
+
+## 5. Risks / call-outs
+
+- **`[PERM]` no-central-store** — the cache is explicitly transient/in-memory.
+  Reviewer must confirm no EF entity/table/migration is introduced.
+- **Proto evolution** — `SubscribeSite` must be purely additive (new RPC + new
+  message; no field renumbering). PLAN-08's ClusterClient/gRPC contract-lock
+  tests apply.
+- **Stream-vs-snapshot race** — the seed-then-stream dedup is the classic bug
+  surface; reuse the `DebugStreamBridgeActor` ordering exactly.
+- **Failover gap** — a NodeA↔NodeB flip must re-seed (not silently serve stale);
+  the 60 s reconcile snapshot is the backstop.
+- **Effort estimate:** ~6–9 focused tasks; Task 4 is the only genuinely hard one.
+  Everything else reuses existing, proven machinery
+  (`SiteStreamManager`/`SiteStreamGrpcClientFactory`/`DebugStreamBridgeActor`/
+  `IDeploymentStatusNotifier`/`AlarmSummaryService`).
+
+## 6. Explicitly out of scope
+- Persisted central alarm store or history (locked `[PERM]`).
+- Aggregated attribute stream (summary needs alarms only).
+- CLI/SignalR surface for the aggregated feed (Blazor-only; revisit if a CLI
+  consumer appears).
+- Ack-back / write path (native alarms remain read-only mirrors).
diff --git a/docs/plans/2026-07-10-kpi-history-hourly-rollups-plan.md b/docs/plans/2026-07-10-kpi-history-hourly-rollups-plan.md
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+# Plan: KPI History Hourly Rollups (deferred #22)
+
+**Status:** Draft plan (not yet executed) — 2026-07-10
+**Register row:** `docs/plans/2026-07-08-deferred-work-register.md` #22
+**Revisit trigger that fired this plan:** *"KpiSample query latency on dashboards."*
+**Owning component:** KPI History (#26); touches Configuration Database (#17),
+Commons (#16), Central UI (#9), and every `IKpiSampleSource` owner.
+
+---
+
+## 1. Problem
+
+`KpiSample` is a tall/EAV table sampled once per minute per series
+(`(Source, Metric, Scope, ScopeKey)` 4-tuple). Long-range trend queries fetch and
+sort every raw row in the window before `KpiSeriesBucketer` downsamples to
+`DefaultMaxSeriesPoints = 200`:
+
+| Window | Raw rows/series @ 1/min |
+|--------|-------------------------|
+| 24 h   | 1,440 |
+| 7 d    | 10,080 |
+| 30 d   | 43,200 |
+| 90 d   | 129,600 |
+
+The four trend surfaces (Notification Outbox, Site Calls, Audit Log, Health) today
+offer only **24 h** and **7 d** windows, so the worst case is ~10k rows/series.
+The latency trigger only truly bites once **30 d / 90 d** windows are added — so
+this plan must decide whether to add those windows *and* pre-aggregate them, or
+rollups have no caller.
+
+## 2. Key facts that shape the design (from the code)
+
+- **The bucketer is not the bottleneck.** `KpiSeriesBucketer.Bucket` derives bucket
+  width purely from `(to − from) / maxPoints` *after* rows are in memory. The cost
+  is entirely in `GetRawSeriesAsync` fetching/sorting rows. Hourly rollups plug in
+  by feeding the bucketer a **pre-thinned ≤1-row/hour series** (≈60× fewer rows).
+- **`KpiHistoryQueryService.GetSeriesAsync` already owns fetch→bucket + options** —
+  the natural place to branch raw-vs-rollup by range.
+- **`KpiHistoryRecorderActor` takes the root `IServiceProvider` and opens a
+  per-tick scope** — a new hourly rollup timer needs **no constructor change**,
+  just a new timer + repo method (same shape as the existing sample/purge timers).
+- **Metrics are not all gauges.** Most are instantaneous gauges (`queueDepth`,
+  `buffered`, `connectionsDown`, `oldestPendingAgeSeconds`) where last-value-per-
+  hour is correct. But several are **already-windowed rate counters**
+  (`deliveredLastInterval`, `failedLastInterval`, `*LastHour`, `scriptErrors`,
+  `deadLetters`) where last-value-per-hour **undercounts** (keeps one minute's
+  delta, discards the other 59). This is the single biggest correctness decision.
+- Some metrics are **conditionally emitted** (`oldestPendingAgeSeconds` skipped
+  when null) — a rollup must not assume a row exists every minute.
+- **This is greenfield** — no `rollup`/`KpiRollup` table/column/code exists.
+
+## 3. Chosen approach
+
+**A separate `KpiRollupHourly` table, populated by an hourly recorder tick, with
+per-metric aggregation intent, queried via a range threshold, retained longer than
+raw samples, and backfilled once at migration.** Also add **30 d / 90 d** windows
+to the four surfaces so the rollups have a caller.
+
+Rationale for each decision (the research surfaced these as the required choices):
+
+**(a) Separate table vs. computed-on-read → separate `KpiRollupHourly` table.**
+Computed-on-read (`GROUP BY DATEADD(hour…)`) needs no migration/backfill but still
+**scans all raw rows** in SQL every query — it shrinks rows *returned*, not rows
+*scanned*, so it only partially addresses the latency trigger. A pre-aggregated
+table (design-consistent with the non-partitioned `KpiSample` model) makes a 90 d
+read a small indexed scan (~2,160 rows vs ~130k).
+
+**(b) Who computes → recorder-side hourly tick.** Add a third Akka timer
+(`RollupTick`) to `KpiHistoryRecorderActor`. Fold the **trailing N hours**
+(lookback window, not just "last hour") so a singleton-failover handover that
+misses a tick re-folds on recovery. Idempotent **upsert** keyed on
+`(Source, Metric, Scope, ScopeKey, HourStartUtc)`. Query-time fold was rejected
+because it doesn't reduce SQL scan (see (a)).
+
+**(c) Range routing → in `KpiHistoryQueryService.GetSeriesAsync`.** New option
+`RollupThresholdHours` (default 168 = 7 d): windows ≤ threshold → `GetRawSeriesAsync`
+(preserves intra-minute detail on 24 h/7 d); windows > threshold →
+`GetHourlySeriesAsync`. `KpiSeriesBucketer.Bucket` then runs unchanged on whichever
+series (note 90 d rollup = 2,160 rows > 200, so bucketing still applies on top).
+
+**(d) Retention → rollups outlive raw.** Keep raw `KpiSample` at 90 d (existing
+purge). Retain `KpiRollupHourly` much longer (new `RollupRetentionDays`, default
+365) via a **second purge pass** mirroring the 1-hour-sliced batch DELETE in
+`PurgeOlderThanAsync`. Validator must enforce `RollupRetentionDays ≥ RetentionDays`.
+This delivers *both* read-speed and history depth; without it the feature only
+buys speed.
+
+**(e) Backfill → one-shot fold at rollout.** Fold existing ≤90 d of `KpiSample`
+into `KpiRollupHourly` once (data migration or idempotent startup fold), so
+30 d/90 d charts aren't blank until enough wall-clock passes. The idempotent
+upsert key makes a re-run safe.
+
+**Cross-cutting correctness — per-metric aggregation.** Classify each charted
+metric as **gauge** (store last-value-per-hour) or **rate** (store sum-per-hour);
+store `Value` plus `Min`/`Max`/`Count` so the fold is faithful and future avg/min/
+max charts are unblocked. A metric→kind classification lives next to the
+`KpiMetrics` catalog. Rate metrics folded with `last-value` would silently
+undercount long-range totals — this must be explicit, not incidental.
+
+## 4. Task breakdown
+
+### Task 1 — `KpiRollupHourly` entity + EF config + migration `[standard]`
+- **Files (new):** `src/ZB.MOM.WW.ScadaBridge.Commons/Entities/Kpi/KpiRollupHourly.cs`,
+  `src/ZB.MOM.WW.ScadaBridge.ConfigurationDatabase/Configurations/KpiRollupHourlyEntityTypeConfiguration.cs`,
+  a new `Migrations/*AddKpiRollupHourlyTable.cs` (append after `20260710…`).
+- **Files (edit):** `.../ConfigurationDatabase/ScadaBridgeDbContext.cs` (DbSet).
+- Columns: 4-tuple series key (same varchar sizes as `KpiSample`) + `HourStartUtc`
+  (`datetime2`, hour-truncated UTC) + `Value` (folded aggregate) + `MinValue` +
+  `MaxValue` + `SampleCount`. Unique index on
+  `(Source, Metric, Scope, ScopeKey, HourStartUtc)` (upsert key + covers range
+  reads); secondary index on `(HourStartUtc)` for purge. Non-partitioned,
+  `[PRIMARY]`, no DB-role restriction (mirror `KpiSample`). **Build before
+  scaffolding the migration** (repo gotcha: `--no-build` emits an empty migration).
+
+### Task 2 — Metric aggregation classification `[small]`
+- **Files:** `src/ZB.MOM.WW.ScadaBridge.Commons/Types/Kpi/KpiMetrics.cs` (or a new
+  `KpiMetricAggregation.cs` beside it).
+- Add a `Gauge`/`Rate` classification and a lookup by `(Source, Metric)` covering
+  all charted metrics across the four sources. Rate: `deliveredLastInterval`,
+  `failedLastInterval`, `totalEventsLastHour`, `errorEventsLastHour`,
+  `scriptErrors`, `alarmEvalErrors`, `deadLetters`, `eventLogWriteFailures`.
+  Gauge: everything else (`queueDepth`, `buffered`, `stuck`, `parked*`,
+  `oldestPendingAgeSeconds`, `connectionsUp/Down`, `deployedInstances`, …).
+  Unknown metric → default `Gauge` (last-value) + log, so a new metric can't crash
+  the fold. Unit-test the classification is total over the current catalog.
+
+### Task 3 — Rollup fold repository method `[standard]`
+- **Files:** `src/ZB.MOM.WW.ScadaBridge.Commons/Interfaces/Repositories/IKpiHistoryRepository.cs`,
+  `src/ZB.MOM.WW.ScadaBridge.ConfigurationDatabase/Repositories/KpiHistoryRepository.cs`
+- `FoldHourlyRollupsAsync(DateTime fromHourUtc, DateTime toHourUtc, ct)`:
+  group `KpiSample` in the window by `(series, hour)`, apply per-metric
+  aggregation (Task 2) → `Value`, plus `MinValue`/`MaxValue`/`SampleCount`;
+  **idempotent upsert** into `KpiRollupHourly` on the unique key. Skip the current
+  (incomplete) hour. Handle the conditionally-emitted metric (missing rows in some
+  minutes) gracefully.
+- `GetHourlySeriesAsync(source, metric, scope, scopeKey, fromUtc, toUtc, ct)` →
+  `IReadOnlyList<KpiSeriesPoint>` (project `HourStartUtc`→`CapturedAtUtc`,
+  `Value`), ordered ascending — same contract as `GetRawSeriesAsync` so the
+  bucketer is agnostic.
+- `PurgeRollupsOlderThanAsync(before, ct)` — 1-hour-sliced batch DELETE (mirror
+  `PurgeOlderThanAsync`).
+
+### Task 4 — Recorder hourly tick + rollup purge `[standard]`
+- **Files:** `src/ZB.MOM.WW.ScadaBridge.KpiHistory/KpiHistoryRecorderActor.cs`,
+  `.../KpiHistoryOptions.cs`, `.../KpiHistoryOptionsValidator.cs`
+- New Akka timer `RollupTick` at `RollupInterval` (default 1 h): per-tick scope →
+  `FoldHourlyRollupsAsync(now − RollupLookbackHours, now)`. Re-fold lookback
+  (default 3 h) makes failover-missed hours self-heal via the idempotent upsert.
+  `_rollupInFlight` guard (mirror `_sampleInFlight`). Extend the daily purge tick
+  to also call `PurgeRollupsOlderThanAsync(now − RollupRetentionDays)`.
+- Options: `RollupInterval` (1 h), `RollupLookbackHours` (3), `RollupRetentionDays`
+  (365), `RollupThresholdHours` (168). Validator: all `> 0`; `RollupRetentionDays`
+  bound `[1, 3650]` **and ≥ `RetentionDays`**; `RollupThresholdHours ≥ 24`.
+
+### Task 5 — Query service range routing `[small]`
+- **Files:** `src/ZB.MOM.WW.ScadaBridge.CentralUI/Services/KpiHistoryQueryService.cs`
+- In `GetSeriesAsync`: if `(toUtc − fromUtc).TotalHours > RollupThresholdHours`,
+  call `GetHourlySeriesAsync`, else `GetRawSeriesAsync`; then `Bucket` as today.
+  Both ctors (production `IServiceScopeFactory`, test `IKpiHistoryRepository`)
+  keep working. Unit-test the routing boundary (168 h raw vs 169 h rollup).
+
+### Task 6 — Backfill existing samples once `[standard]`
+- **Files:** startup fold in Host (grep `AkkaHostedService` KPI wiring) OR a data
+  migration.
+- One idempotent `FoldHourlyRollupsAsync(now − RetentionDays, now)` at first
+  startup after deploy (guarded so it runs once / is cheap to re-run). Log rows
+  folded. Prefer the startup fold over a data-migration so it reuses Task 3 logic.
+
+### Task 7 — Add 30 d / 90 d windows to the four surfaces `[standard]`
+- **Files:** `.../Pages/Audit/AuditLogPage.razor.cs`,
+  `.../Pages/SiteCalls/SiteCallsReport.razor.cs`,
+  `.../Pages/Notifications/NotificationKpis.razor`,
+  `.../Pages/Monitoring/Health.razor`
+- Add 30 d (720 h) and 90 d (2160 h) toggle buttons alongside the existing 24 h /
+  7 d. No fetch-call changes — they already pass `fromUtc/toUtc` to the query
+  service, which now transparently routes to rollups for the long windows. This is
+  what actually *exercises* the rollup path (without it, rollups have no caller).
+
+### Task 8 — Tests + docs `[standard]`
+- **Files:** `tests/.../Commons.Tests/*` (bucketer unchanged; classification;
+  fold aggregation math — especially rate-sum vs gauge-last),
+  `tests/.../ConfigurationDatabase.Tests/*` (fold upsert idempotency, purge,
+  `GetHourlySeriesAsync`), `tests/.../KpiHistory.Tests/*` (rollup tick + purge +
+  in-flight guard + failover re-fold), `tests/.../CentralUI.Tests/*` (query
+  routing; new window buttons).
+- Docs: `docs/requirements/Component-KpiHistory.md` (schema section for the rollup
+  table, retention section, query section: raw≤threshold / rollup>threshold, new
+  windows), `docs/plans/2026-06-17-m6-kpi-history-design.md` (mark downsampling
+  deferral delivered), and move register #22 to **Resolved**.
+
+## 5. Risks / call-outs
+- **Rate-metric undercount** — the plan's biggest correctness risk; Task 2's
+  classification + Task 3's per-metric fold must be reviewed together. A rate
+  metric folded as last-value silently misreports long-range totals.
+- **Failover-missed hour** — the lookback re-fold + idempotent upsert is the
+  backstop; verify a simulated missed tick self-heals.
+- **Retention coherence** — `RollupRetentionDays ≥ RetentionDays` must be
+  validator-enforced or long-range charts get holes where raw is purged but
+  rollups weren't yet written.
+- **Migration hygiene** — build before `migrations add`; delete empty scaffolds
+  (repo gotcha).
+- **No new infra** — like `KpiSample`, the rollup table lives in central MS SQL,
+  non-partitioned; no new services.
+
+## 6. Explicitly out of scope
+- Multi-resolution rollups (daily/weekly) — hourly only; revisit if 1-year+
+  windows appear.
+- Charting `Min`/`Max`/`Avg` bands — the columns are stored to unblock it, but the
+  `KpiTrendChart` still plots a single series in this plan.
+- Changing live-sample cadence or the point-in-time KPI reads (unaffected).