docs(mesh-phase5): telemetry stream — Telemetry.md, config keys, supersede §6.3, program status

Claude-Session: https://claude.ai/code/session_01GASWkNEi68FSCtvr6rLoEW
2026-07-23 16:33:29 -04:00
parent 1104785c89
commit e99ea40e2f
6 changed files with 380 additions and 11 deletions
@@ -177,6 +177,60 @@ PersistNodeAck`) and LDAP group→role DB grants (a driver-only node maps LDAP g
 the `Security:Ldap:GroupToRole` appsettings baseline only — see `docs/Redundancy.md` and
 `CLAUDE.md` §"Phase 4" for the full picture, including the client-visible ServiceLevel change).

+### `Telemetry` / `TelemetryDial` (live telemetry transport)
+
+- **Purpose:** [per-cluster mesh](plans/2026-07-21-per-cluster-mesh-design.md) **Phase 5**. Selects how
+  the four live-observability channels (`alerts`, `script-logs`, `driver-health`,
+  `driver-resilience-status`) reach central: `Dps` (DistributedPubSub — the four existing SignalR
+  bridges, today's behaviour) or `Grpc` (a driver node hosts one gRPC server-streaming contract over a
+  dedicated h2c port; central dials in and feeds the same in-process sinks). `Telemetry` is the
+  **node/serve** side; `TelemetryDial` is the **central/dial** side.
+- **Options classes:** `TelemetryOptions` (`SectionName = "Telemetry"`) + `TelemetryDialOptions`
+  (`SectionName = "TelemetryDial"`), both in `src/Core/ZB.MOM.WW.OtOpcUa.Cluster/`. Bound by
+  `AddOtOpcUaCluster(config)`; their validators run at `ValidateOnStart`.
+
+**`Telemetry` (node-side, serve):**
+
+| Key | Type | Default | Meaning |
+|---|---|---|---|
+| `Mode` | string | `Dps` | `Dps` = no change, node just keeps publishing DPS as it always has. `Grpc` = central-ingest hint (see `TelemetryDial:Mode` below — this key does not gate anything on the node itself). Any other value **refuses to start**. |
+| `GrpcListenPort` | int | `0` | Dedicated **h2c-only** Kestrel port for the telemetry stream service. `0` = disabled (nothing bound). The node hosts the server whenever this is `> 0`, **regardless of `Mode`**. |
+| `ApiKey` | string | `""` | Shared bearer key the serve-side interceptor checks (constant-time, **fail-closed**: an unset key rejects every call). **Supply via env `Telemetry__ApiKey` — never commit.** |
+
+**`TelemetryDial` (central-side, dial):**
+
+| Key | Type | Default | Meaning |
+|---|---|---|---|
+| `Mode` | string | `Dps` | `Dps` = the four DPS SignalR bridges (alert, script-log, driver-status, resilience) subscribe as today. `Grpc` = those four bridges are **not spawned**; the `TelemetryDialSupervisor` actor dials every driver node instead and feeds the same sinks. Any other value **refuses to start**. |
+| `ApiKey` | string | `""` | Shared bearer key; must equal the nodes' `Telemetry:ApiKey`. **Supply via env `TelemetryDial__ApiKey` — never commit.** Required under `Grpc`. |
+| `ContactRefreshSeconds` | int | `60` | How often central rebuilds its dial-target set from the `ClusterNode` rows (`Host` + `GrpcPort`). |
+| `CallTimeoutSeconds` | int | `30` | Per-call deadline for the streaming RPC's keepalive/health bookkeeping. |
+
+**It is a dark switch; the node always hosts.** Unlike `ConfigServe`/`MeshTransport`, where the serve
+side is gated on a role, the telemetry server binds whenever `Telemetry:GrpcListenPort > 0` — hosting
+is unconditional on a driver-role node, in both modes, because the node also always emits into its
+local hub and always publishes DPS. Only `TelemetryDial:Mode` on central actually changes behaviour:
+which of the two already-always-available sources (DPS bridges vs. the gRPC dial supervisor) feeds the
+AdminUI sinks. Flipping either side is a config change plus restart, not a redeploy — the same
+discipline as `MeshTransport:Mode` and `ConfigSource:Mode`.
+
+**A driver-role node with `Telemetry:Mode=Grpc` must set `GrpcListenPort > 0`** (nothing to serve
+otherwise) — enforced by `TelemetryOptionsValidator`. **`Grpc` mode on either side requires a
+non-empty `ApiKey`** — fail-closed, same as `ConfigServe`/`LocalDb:Replication`.
+
+**Three DPS observability topics stay out of scope for this transport, on purpose:**
+`redundancy-state` (pair-local, built from `Cluster.State`, stays on DPS in both modes — see
+[`Redundancy.md`](Redundancy.md#command-transport-centralnode)), `fleet-status` (central-internal;
+`Fleet.razor` polls the Config DB, not any stream), and `deployment-acks` (already rides the Phase 2
+`ClusterClient` transport as a command-plane reply). See
+[`docs/Telemetry.md`](Telemetry.md) for the full architecture, the reconnect/generation-stamped
+dialer story, and the rationale for the node-hosts/central-dials inversion.
+
+On the docker-dev rig every driver-role node carries `Telemetry:GrpcListenPort` (`4056`) + a
+committed dev key, and central carries the matching `TelemetryDial:ApiKey`; both `Mode` keys stay
+unset (⇒ `Dps`) until the rig is flipped with `Telemetry__Mode=Grpc` / `TelemetryDial__Mode=Grpc` at
+`docker compose up`.
+
 ### `ConnectionStrings` → `ConfigDb`

 - **Purpose:** the central Config DB connection string. **Required on admin-role nodes only** — `Program.cs` calls `AddOtOpcUaConfigDb` when `hasAdmin` (per-cluster mesh Phase 4). A driver-only node holds no `ConfigDb` connection string; it fetches its configuration via `ConfigSource:Mode=FetchAndCache` instead (see above). A fused `admin,driver` node still requires it.
@@ -283,6 +337,7 @@ These are consumed by the driver **integration-test fixtures** (under `tests/Dri

 - [`security.md`](security.md) — transport security, OPC UA authentication, LDAP (`Security:Ldap`), data-plane ACLs, control-plane roles.
 - [`Redundancy.md`](Redundancy.md) — the `Cluster` section in the context of warm/hot redundancy, ServiceLevel, peer discovery.
+- [`Telemetry.md`](Telemetry.md) — the `Telemetry`/`TelemetryDial` gRPC live-telemetry stream: direction, dark switch, the four migrated channels + three deferrals, auth, reconnect story.
 - [`ServiceHosting.md`](ServiceHosting.md) — role-based host wiring and `OTOPCUA_ROLES`.
 - [`docs/drivers/Galaxy.md`](drivers/Galaxy.md) — Galaxy/MxAccess driver overview.
 - [`docs/v2/config-db-schema.md`](v2/config-db-schema.md) — the full Config DB schema.
@@ -465,6 +465,15 @@ are untouched, and `redundancy-state` itself stays on DPS (it is bidirectional a
 `Cluster.State`, which makes it genuinely mesh-bound — the hardest remaining dependency before the
 meshes can split).

+**Observability telemetry took the opposite path (Phase 5).** The four live-panel channels
+(`alerts`, `script-logs`, `driver-health`, `driver-resilience-status`) moved off DPS onto a
+dedicated gRPC server-streaming contract — each driver node hosts, central dials in — selected by
+`Telemetry:Mode`/`TelemetryDial:Mode` (default `Dps`). `redundancy-state` is deliberately **not**
+part of that migration: it stays on DPS in every mode because it is pair-local and Cluster.State-built,
+not a fleet-wide observability broadcast. See [`docs/Telemetry.md`](Telemetry.md) for the full
+architecture and [`Configuration.md` § `Telemetry`/`TelemetryDial`](Configuration.md#telemetry--telemetrydial-live-telemetry-transport)
+for the config keys.
+
 **Config bytes travel out-of-band (Phase 3).** Commands stay on one of the two transports above, but
 the *configuration artifact itself* does not ride any Akka message — `DispatchDeployment` is
 payload-free (`DeploymentId` + `RevisionHash`). Under `ConfigSource:Mode = FetchAndCache` (see
@@ -0,0 +1,190 @@
+# Live Telemetry Transport (v2)
+
+## Overview
+
+The AdminUI's live observability panels (`/alerts`, `/script-log`, `/hosts` driver table, driver
+resilience status) are fed by four node→central event channels. Historically all four rode
+DistributedPubSub (DPS) on the shared Akka mesh — the same gossip ring that carries redundancy
+state and the command-plane topics. Per-cluster mesh **Phase 5** adds a second transport for these
+four channels only: one gRPC server-streaming contract, selected per node/central pair by
+`Telemetry:Mode` / `TelemetryDial:Mode` (`Dps` default | `Grpc`).
+
+This is the same motivation as [Phase 2's `MeshTransport`](Configuration.md#meshtransport-centralnode-command-transport)
+and [Phase 3's `ConfigSource`/`ConfigServe`](Configuration.md#configsource--configserve-config-fetch-and-cache):
+DPS only works when central and the node share a gossip ring, and [Phase 6](plans/2026-07-21-per-cluster-mesh-design.md)
+splits the fleet into one Akka mesh per application `Cluster`. Once that split lands, a driver node
+in a site's mesh is no longer a cluster member of central's mesh, so DPS can no longer reach it —
+telemetry needs its own out-of-band transport, same as commands (Phase 2) and config bytes (Phase 3).
+
+## Direction: the node hosts, central dials
+
+**Load-bearing and easy to get backwards:** each **driver** node hosts the telemetry gRPC server
+(a dedicated Kestrel h2c listener); **central (admin role) is the client** and dials in. This
+mirrors the inversion ScadaBridge already uses for the same problem (its `SiteStreamService`).
+
+```
+ driver node                          central (admin)
+┌─────────────────────┐              ┌──────────────────────────┐
+│ 4 publish seams      │              │ TelemetryDialSupervisor   │
+│  -> node-local hub    │   Subscribe  │  - discovers ClusterNode   │
+│  -> DPS (unchanged)   │◄─────────────│    rows (Host+GrpcPort)   │
+│                       │   (gRPC      │  - one reconnecting       │
+│ TelemetryStreamGrpc-  │    stream)   │    dialer per node        │
+│  Service (h2c server) │─────────────►│  - feeds the SAME sinks   │
+│  Telemetry:GrpcListen- │  TelemetryEvent │   the DPS bridges feed   │
+│  Port                 │  (oneof, 4 kinds)│   today                  │
+└─────────────────────┘              └──────────────────────────┘
+```
+
+A fused `admin,driver` node both hosts (as driver) and dials (as admin) — it dials itself plus its
+redundant pair peer, the same way central dials site nodes.
+
+Central discovers driver-node telemetry endpoints from the `ClusterNode` table (`Host` +
+`GrpcPort`, the latter added in Phase 1 for exactly this purpose) — the same DB-sourced discovery
+Phase 1's ack set and Phase 2's `ClusterClient` contact set already use. No shared gossip
+membership is required to find or dial a node.
+
+## The dark switch
+
+`Telemetry:Mode` (node/serve side) and `TelemetryDial:Mode` (central/dial side) each default to
+`Dps` and can be independently set to `Grpc`. Both code paths are compiled into every binary —
+flipping either flag is an appsettings/env change plus a restart, **not a redeploy or rebuild** —
+the same discipline as `MeshTransport:Mode` and `ConfigSource:Mode`.
+
+What actually changes per mode, precisely:
+
+- **The node ALWAYS does both things, regardless of `Telemetry:Mode`.** Every one of the four
+  publish seams emits into the node-local `ITelemetryLocalHub` **and** publishes to DPS,
+  unconditionally. The node additionally **always** hosts the gRPC server whenever
+  `Telemetry:GrpcListenPort > 0` — hosting is not mode-gated at all. `Telemetry:Mode` only affects
+  central's own bookkeeping about which side it expects to be consulted (it is otherwise inert on
+  the node).
+- **Only central's ingest source switches**, driven by `TelemetryDial:Mode`:
+  - `Dps` (default) — today's four DPS SignalR bridges (alert, script-log, driver-status,
+    resilience) subscribe and feed the AdminUI sinks. Unchanged behavior.
+  - `Grpc` — those four DPS bridges are **not spawned**. Instead the `TelemetryDialSupervisor`
+    actor dials every driver node's gRPC stream and feeds the **identical** in-process sinks
+    (`IInProcessBroadcaster<AlarmTransitionEvent>`, `IInProcessBroadcaster<ScriptLogEntry>`,
+    `IDriverStatusSnapshotStore`, `IDriverResilienceStatusStore`).
+- **The AdminUI panels themselves are untouched.** `/alerts`, `/script-log`, and the `/hosts`
+  driver table all read from the same sinks in both modes — only the sinks' upstream feed swaps.
+  The `fleet-status` bridge (out of Phase 5 scope — see below) stays on DPS in both modes.
+
+Because hosting is unconditional and both ingest paths are always compiled in, a fleet can be
+flipped node-by-node and central-by-central with no coordination window where telemetry is lost —
+the node is always serving, so central can switch to `Grpc` whenever it likes.
+
+## The four migrated channels
+
+| DPS topic (today) | Domain record | Central sink fed |
+|---|---|---|
+| `alerts` | `AlarmTransitionEvent` | `IInProcessBroadcaster<AlarmTransitionEvent>` (+ `AlertHub`); `/alerts` page; live/disconnected pill |
+| `script-logs` | `ScriptLogEntry` | `IInProcessBroadcaster<ScriptLogEntry>` (+ `ScriptLogHub`); `/script-log` page; live pill |
+| `driver-health` | `DriverHealthChanged` | `IDriverStatusSnapshotStore`; `/hosts` driver table |
+| `driver-resilience-status` | `DriverResilienceStatusChanged` | `IDriverResilienceStatusStore` |
+
+These four are carried as `oneof` event kinds on one `TelemetryStreamService.Subscribe` RPC — a
+single stream per (central, driver-node) pair carries all four, rather than one stream per topic.
+Proto field evolution is additive-only (never renumber/reuse a tag), locked by a contract test that
+reflects over the `oneof` cases.
+
+## The three deferred channels (NOT migrated in Phase 5 — do not read this as "seven done")
+
+The program sketch originally named seven observability topics for Phase 5. Three were scoped out,
+each for a distinct, settled reason:
+
+- **`redundancy-state`** — bidirectional, built directly from `Cluster.State`, and **pair-local**:
+  it drives ServiceLevel and the Primary data-plane gate, consumed in-process by
+  `OpcUaPublishActor`, `ScriptedAlarmHostActor`, `DriverHostActor`, and `HistorianAdapterActor`.
+  It stays on DPS in **both** `MeshTransport` modes today, and it is genuinely mesh-bound by
+  design — under Phase 6 each pair keeps sharing its own small mesh, so DPS keeps working for it
+  in-mesh. Central's *display* of each pair's redundancy state is a Phase 6 cross-mesh concern
+  (a future observability channel, once central no longer shares gossip with any site pair), not a
+  Phase 5 telemetry-panel migration.
+- **`fleet-status`** — **central-internal**, not a node→central stream at all. The admin singleton
+  `FleetStatusBroadcaster` builds it from the admin node's own cluster membership/reachability/
+  leader events, and `Fleet.razor` **polls the Config DB** and ignores the feed entirely. There is
+  nothing here for a per-node gRPC stream to carry. Revisit in Phase 6, once central genuinely
+  loses gossip visibility of site nodes and needs another way to know a pair's membership.
+- **`deployment-acks`** — already migrated, but onto a different transport: it rides the Phase 2
+  `ClusterClient` transport (`MeshTransport:Mode=ClusterClient`) as a command-plane reply, not an
+  observability broadcast. It was never a Phase 5 candidate.
+
+See [`docs/Redundancy.md`](Redundancy.md#command-transport-centralnode) for how `redundancy-state`
+and the command transports fit together.
+
+## Authentication — fail-closed from day one
+
+A shared node bearer key gates the stream: `Telemetry:ApiKey` (node/serve side) must equal
+`TelemetryDial:ApiKey` (central/dial side). `TelemetryStreamAuthInterceptor` enforces it — path-scoped
+to `/telemetry.v1.TelemetryStreamService/`, comparing the `Authorization: Bearer` token with
+`CryptographicOperations.FixedTimeEquals`, and rejecting with `PermissionDenied`. An **unset** key
+rejects every call rather than allowing an open stream — the same fail-closed posture as
+`ConfigServeAuthInterceptor` and `LocalDbSyncAuthInterceptor`.
+
+This **supersedes** [the design doc's §6.3](plans/2026-07-21-per-cluster-mesh-design.md), which had
+provisionally decided to "match ScadaBridge's unauthenticated posture for now" for inter-cluster
+transports. ScadaBridge itself has since closed that gap with this identical
+interceptor pattern, so Phase 5 ships authenticated from the start rather than deferring auth to a
+later hardening pass. See the design doc's superseded note for the full history.
+
+## Reconnect and reliability
+
+Central's `TelemetryDialSupervisor` (an admin-role actor) runs **one reconnecting dialer per
+driver node**:
+
+- **Discovery** — enabled, non-maintenance `ClusterNode` rows are read on start and refreshed every
+  `TelemetryDial:ContactRefreshSeconds` (default 60), plus on an admin-side topology change. A row
+  with a null `GrpcPort` is skipped (that node exposes no telemetry endpoint — logged, not an
+  error). Dial targets are added/removed as the row set changes.
+- **Reconnect backoff** — immediate first retry, then a fixed ~5 second backoff, indefinitely. The
+  dialer never gives up permanently: this is an observability channel, not the data plane, so a
+  persistently-unreachable node just means a persistently-stale panel, not a fleet fault.
+- **Generation stamping** — each dialer carries a monotonically-increasing generation counter, so
+  a late error or late event from a superseded stream (e.g. one that raced a reconnect) is
+  recognized and ignored rather than corrupting the current stream's state.
+- **Snapshot replay on reconnect** — the node-local hub keeps a last-value cache for
+  `driver-health` and `driver-resilience-status` (there is nothing meaningful to replay for
+  `alerts`/`script-logs`, which are append logs). On every new `Subscribe` — including a
+  reconnect — the hub drains the cached snapshots to the new stream before live deltas, so
+  `IDriverStatusSnapshotStore` / `IDriverResilienceStatusStore` re-prime immediately rather than
+  sitting stale until the next natural event. `alerts`/`script-logs` simply tolerate the gap — a
+  reconnect loses whatever transitions happened while disconnected, same as a DPS resubscribe would.
+- **Connection indicator** — the `/alerts` and `/script-log` live/disconnected pill is driven by
+  **aggregate** stream health across all dialers: connected when **at least one** node stream is
+  up, disconnected when all are down. This matches today's DPS `SubscribeAck`/`PostStop` pill
+  semantics — the pill has never meant "every node is live," only "the panel has a source." The
+  two store-backed panels (`driver-health`, `driver-resilience-status`) carry no fleet-wide
+  connection flag today, on gRPC or on DPS; per-row staleness is unchanged.
+
+## Configuration reference
+
+See [`docs/Configuration.md` § `Telemetry` / `TelemetryDial`](Configuration.md#telemetry--telemetrydial-live-telemetry-transport)
+for the full keys table. In brief:
+
+- **`Telemetry`** (node/serve side): `Mode` (`Dps`|`Grpc`, default `Dps`), `GrpcListenPort` (`0` =
+  disabled — the driver node's dedicated telemetry h2c port), `ApiKey` (the shared node key; supply
+  via `${secret:}`/env, never commit).
+- **`TelemetryDial`** (central side): `Mode` (`Dps`|`Grpc`), `ApiKey` (must equal the nodes'
+  `Telemetry:ApiKey`), `ContactRefreshSeconds` (default `60`), `CallTimeoutSeconds` (default `30`).
+
+A driver-role node with `Telemetry:Mode=Grpc` must set `GrpcListenPort > 0` (nothing to serve
+otherwise), and `Grpc` mode on either side requires a non-empty `ApiKey` — both are enforced by
+`ValidateOnStart` validators, fail-fast at boot.
+
+## Relationship to the rest of the mesh program
+
+- **Same dark-switch discipline as Phases 2 and 3.** `MeshTransport:Mode`, `ConfigSource:Mode`, and
+  `Telemetry:Mode`/`TelemetryDial:Mode` are all independently-flippable, restart-only config
+  changes, and in every case the "new" side is always wired so the flip needs no coordinated
+  redeploy.
+- **Why the inversion matters for Phase 6.** Every other cross-boundary transport in this program
+  (`MeshTransport`, `ConfigSource`/`ConfigServe`) already has central as the addressable, discoverable
+  side and the node as the caller or the callee-by-address. Telemetry is the one channel that is
+  naturally node-sourced and fleet-wide-fanned, so putting central in the client role — dialing out
+  to each node by its `ClusterNode`-recorded address — is what lets telemetry survive the mesh split
+  cleanly: central never needs cluster membership with a site's mesh to keep watching it.
+- **Status:** code-complete on `feat/mesh-phase5`; the live gate (flip the docker-dev rig to `Grpc`,
+  confirm all panels stay green with the DPS telemetry bridges unspawned, kill-and-reconnect a site
+  node) has not yet run. See `docs/plans/2026-07-22-per-cluster-mesh-program.md` § Phase 5 and
+  `docs/plans/2026-07-23-mesh-phase5-grpc-telemetry-stream.md` for the implementation plan.
@@ -285,6 +285,20 @@ trusted network. Recorded as an accepted risk rather than an oversight, with two
 it is revisited: `LocalDbSyncAuthInterceptor` is already in our tree as a fail-closed template, and
 the surface most worth gating first is any Pull-style RPC that returns historical rows.

+**SUPERSEDED 2026-07-23.** The Phase 5 telemetry stream (`TelemetryStreamService` — the four
+node→central observability channels) shipped **authenticated from day one**: a shared node bearer
+key (`Telemetry:ApiKey` == `TelemetryDial:ApiKey`), enforced by a fail-closed
+`TelemetryStreamAuthInterceptor` (`CryptographicOperations.FixedTimeEquals`, `PermissionDenied` on
+mismatch, and — load-bearing — an **unset** key rejects every call rather than allowing an open
+stream). This is exactly the `LocalDbSyncAuthInterceptor`/`ConfigServeAuthInterceptor` pattern this
+section flagged as the fail-closed template to reach for, applied immediately rather than deferred.
+ScadaBridge itself has since closed the same "unauthenticated inter-cluster transport" gap with this
+identical interceptor pattern, so this decision no longer matches ScadaBridge's current posture
+either — it matches where ScadaBridge moved to. See [`docs/Telemetry.md`](../Telemetry.md) §
+Authentication for the full detail. The "return historical rows" surface this section called out as
+worth gating first (Pull-style RPCs) remains open for `ConfigServe`/`ConfigSource` and any future
+such surface — only the telemetry stream is closed by this note.
+
 ## 7. Sequencing sketch

 Deliberately not a task plan — per-phase plans follow, one at a time.
@@ -202,16 +202,66 @@ Phase 4 as code-complete, not verified, until this lands.**
 **no ConfigDb connection string configured at all**; grep-level proof no driver-branch service can
 resolve the ConfigDb context.

-### Phase 5 — gRPC stream contract for live telemetry
-**Scope:** one server-streaming contract carrying a `oneof` event, **cluster nodes host the gRPC
-server, central dials in** (the inverted direction is the load-bearing ScadaBridge finding —
-design §2); migrate the seven observability topics (`alerts`, `driver-health`,
-`driver-resilience-status`, `fleet-status`, `script-logs`, plus redundancy-state distribution and
-deployment-acks if Phase 2 left them on DPS); additive-only field evolution, contract locked by
-test; per-panel reconnect story for the AdminUI (design §8 — losing gossip loses free fleet
-observability).
-**Exit gate:** all AdminUI live panels green against a pair with DPS telemetry topics deleted;
-kill-and-reconnect of the central dialer recovers every stream.
+### Phase 5 — gRPC stream contract for live telemetry — **code-complete on `feat/mesh-phase5`, live gate pending**
+**Scope as shipped (narrowed from the program sketch's "seven observability topics," settled with the
+user 2026-07-23 — mirrors how Phases 1 and 3 also honestly scoped down):** one server-streaming gRPC
+contract carrying a `oneof` event with **four** kinds, **driver nodes host the gRPC server (dedicated
+Kestrel h2c port), central dials in** — the inverted direction is the load-bearing ScadaBridge finding
+(design §2), required so telemetry survives the Phase 6 mesh split without shared gossip membership.
+
+**The four migrated channels:**
+
+| DPS topic | Domain record | Central sink |
+|---|---|---|
+| `alerts` | `AlarmTransitionEvent` | `IInProcessBroadcaster<AlarmTransitionEvent>` (+ `AlertHub`) |
+| `script-logs` | `ScriptLogEntry` | `IInProcessBroadcaster<ScriptLogEntry>` (+ `ScriptLogHub`) |
+| `driver-health` | `DriverHealthChanged` | `IDriverStatusSnapshotStore` |
+| `driver-resilience-status` | `DriverResilienceStatusChanged` | `IDriverResilienceStatusStore` |
+
+**Three deferred, each with a settled reason (NOT migrated — do not read the program sketch's original
+"seven" as the delivered scope):**
+- `redundancy-state` — bidirectional, built from `Cluster.State`, pair-local control plane driving
+  ServiceLevel + the Primary gate. Stays on DPS in every mode; under Phase 6 it works in-mesh per pair.
+  Central's cross-pair *display* of redundancy is a Phase 6 concern, not a Phase 5 panel.
+- `fleet-status` — central-internal; `FleetStatusBroadcaster` builds it from the admin node's own
+  cluster membership events and `Fleet.razor` polls the Config DB, ignoring the feed. Not a
+  node→central stream at all. Revisit in Phase 6 once central loses site-node gossip visibility.
+- `deployment-acks` — already migrated, but onto the Phase 2 `ClusterClient` transport, as a
+  command-plane reply, not an observability broadcast.
+
+**Dark switch:** `Telemetry:Mode` (node/serve, default `Dps`) and `TelemetryDial:Mode` (central/dial,
+default `Dps`) flip independently to `Grpc`; both code paths are compiled into every binary, so
+flipping is a config + restart, not a redeploy. The node **always** hosts the gRPC server whenever
+`Telemetry:GrpcListenPort > 0` and **always** emits into its node-local hub + publishes DPS, in both
+modes — only central's ingest source (`TelemetryDial:Mode`) actually switches which of the two
+always-available sources feeds the AdminUI sinks. The AdminUI panels/components are unchanged; only
+the sinks' upstream feed swaps.
+
+**Auth from day one, fail-closed:** a shared node bearer key (`Telemetry:ApiKey` ==
+`TelemetryDial:ApiKey`), gated by `TelemetryStreamAuthInterceptor`
+(`CryptographicOperations.FixedTimeEquals`, `PermissionDenied` on mismatch, unset key rejects every
+call). This supersedes design §6.3's "match ScadaBridge's unauthenticated posture for now" — ScadaBridge
+itself has since closed that gap with this identical interceptor pattern (see the supersede note added
+to design §6.3, and `docs/Telemetry.md` § Authentication).
+
+**Reconnect story:** central's `TelemetryDialSupervisor` runs one reconnecting dialer per driver node,
+discovered from `ClusterNode` rows (`Host`+`GrpcPort`, refreshed every
+`TelemetryDial:ContactRefreshSeconds`); immediate first retry then ~5s fixed backoff, generation-stamped
+so a superseded stream's late error/event is ignored; the dialer never permanently gives up
+(observability, not data plane). The node-local hub replays last-value snapshots for
+`driver-health`/`driver-resilience-status` on every (re)subscribe so those stores re-prime immediately;
+`alerts`/`script-logs` are append logs and tolerate the gap. The `/alerts`/`/script-log` pill reflects
+aggregate stream health (live when ≥1 node stream is up), matching today's DPS pill semantics.
+
+**Docs shipped:** `docs/Telemetry.md` (new, canonical guide), `docs/Configuration.md` §
+`Telemetry`/`TelemetryDial`, `docs/Redundancy.md` cross-reference, this section, and the design §6.3
+supersede note.
+
+**Exit gate (not yet run):** all AdminUI live panels green against the docker-dev rig with
+`Telemetry:Mode=Grpc`/`TelemetryDial:Mode=Grpc` and the four DPS telemetry bridges NOT spawned;
+kill-and-reconnect of a site node's dialer recovers every stream (driver-health/resilience re-prime
+from the node hub's snapshot replay). Treat Phase 5 as **code-complete, not verified**, until this
+lands — see `docs/plans/2026-07-23-mesh-phase5-grpc-telemetry-stream.md` Task 12.

 ### Phase 6 — Mesh partition + co-location topology
 **Scope:** per-cluster seed nodes — ~~adopt ScadaBridge's self-first ordering and RETIRE the
@@ -267,6 +317,6 @@ resource sizing on the site VMs should be checked once both products run the ful
 | 2 ClusterClient transport | **DONE 2026-07-22** (live gate PASSED, shipped dark) — shipped dark (`MeshTransport:Mode=Dps` default), both comm actors registered in both modes. Corrections: `SendToAll` not `Send`, one fleet-wide client not one per cluster, `/user/node-communication` not `/user/cluster-communication`. The gate's "Ask timing out" item does not exist to test — no cross-boundary Ask in this phase; see the phase section. |
 | 3 fetch-and-cache | **DONE 2026-07-23**, merged `d01b0695`, live gate PASSED, pushed to origin (scadaproj umbrella index updated + pushed `b5e7bc8`). gRPC fetch RPC + shared node key; dark switch `ConfigSource:Mode` (Direct default). Rig flip: `OTOPCUA_CONFIG_MODE=FetchAndCache` on the site nodes. See `2026-07-22-mesh-phase3-config-fetch-and-cache.md`. |
 | 4 cut driver ConfigDb | **DONE 2026-07-23 — live gate PASSED** on `feat/mesh-phase4` (Tasks 0–8 + 1b + 10–11; Task 9 table-drop deferred). ConfigDb admin-only; driver-only ⇒ FetchAndCache (validator); `DbHealthProbeActor` not spawned driver-only (client-visible ServiceLevel 240/250 with central SQL down — proven live); alarm condition state in replicated LocalDb `alarm_condition_state`; central persists acks; `OpcUaPublish` guard split fixes the driver-only address-space wipe; driver-only LDAP maps from appsettings only (6th consumer found mid-phase). Gate: deploy sealed green w/ 4 DB-less site nodes acking, ServiceLevel held 240 w/ SQL down, restart booted last-known-good from the LocalDb pointer. See `2026-07-23-mesh-phase4-cut-driver-configdb.md` + `2026-07-23-mesh-phase4-live-gate.md`. |
-| 5 gRPC telemetry | not started |
+| 5 gRPC telemetry | **code-complete (live gate pending)** on `feat/mesh-phase5`. 4-channel scope (`alerts`/`script-logs`/`driver-health`/`driver-resilience-status`), 3 deferred with rationale (`redundancy-state`, `fleet-status`, `deployment-acks`); dark switch `Telemetry:Mode`/`TelemetryDial:Mode` (Dps default); auth-from-day-one fail-closed bearer key, superseding design §6.3. See `docs/Telemetry.md` + `2026-07-23-mesh-phase5-grpc-telemetry-stream.md`. |
 | 6 mesh partition + co-location | not started |
 | 7 drill + live gates | not started |