feat(grpc): PSK-authenticate the site gRPC control plane; drop the vestigial management receptionist registration

Phase 0 of the ClusterClient→gRPC migration
(docs/plans/2026-07-22-clusterclient-to-grpc-plan.md). Standalone hardening: it
closes a gap that exists today and is a precondition for moving command/control
onto gRPC in later phases.

T0.1 — delete the ManagementActor ClusterClientReceptionist registration.
It was built for an out-of-cluster CLI that was never written: the shipped CLI
speaks HTTP Basic to /management, which asks the actor in-process through
ManagementActorHolder. Nothing in the repo ever sent to /user/management. The
actor still runs there; only the cross-boundary advertisement is gone. Six
documents claimed the CLI used ClusterClient — including the CLI's own README
"Architecture Notes" — and are corrected here rather than left to rot.

T0.2 — record, do not port, the dead integration-routing path.
IntegrationCallRequest is unwired at BOTH ends: RouteIntegrationCallAsync has
zero callers anywhere, and RegisterLocalHandler(Integration, …) appears only in
a test, so production always answers "Integration handler not available". It is
excluded from the gRPC contract (28 of 29 commands migrate) rather than
enshrined on an additive-only wire format, and deleting it during a
transport migration would mix a behavioural change into a change whose whole
value is that behaviour is identical. See
docs/known-issues/2026-07-22-integration-call-routing-is-dead-code.md.

T0.3 — preshared-key authentication on SiteStreamService.
The service shipped with no auth at all: plaintext h2c, no interceptor, so
anything that could reach a site node's :8083 could open a live data stream or
read audit rows back via PullAuditEvents/PullSiteCalls. ControlPlaneAuthInterceptor
now gates /sitestream.SiteStreamService/ — modeled on LocalDbSyncAuthInterceptor
(constant-time compare, fail-closed, PermissionDenied) but gating a SET of
service prefixes so phases 1A/1B add services rather than interceptors. LocalDb
sync keeps its own separate key: it authenticates the pair partner, not central,
and collapsing the two would make a site's central-facing key also admit writes
into its database.

Keys are per site (SB-GRPC-PSK-<siteId>), never fleet-wide, so a compromised
site yields only its own. Central attaches them through ControlPlaneCredentials,
which binds CallCredentials to the channel — covering unary and streaming
uniformly, and letting the key resolve asynchronously, which a client
interceptor could not do without blocking. All three central→site channel
creation sites go through it (SiteStreamGrpcClient and both audit pull invokers);
the pull invokers' channel caches are re-keyed by (site, endpoint) because
credentials are per-site and bound to the channel.

Two decisions beyond the plan:

  * StartupValidator now requires GrpcPsk on Site nodes. The plan specified only
    the runtime gate, but fail-closed with no boot check produces a node that
    joins, answers heartbeats and reports healthy while refusing every stream,
    audit pull and telemetry ingest — silent and total. Same reasoning as the
    existing inbound API-key pepper rule.

  * Added Communication:SitePsks as a central-side key map. The plan assumed
    central would read the store, seeded via a dev KEK; the docker rig
    deliberately boots with no master key, so store-only resolution would leave
    it unable to dial its own sites. The store stays primary — it is the only
    source that can serve a site added at runtime — with the map covering
    key-less hosts and one-off pins. Neither source falling back to
    "unauthenticated" is the invariant.

T0.4 — dev keys on both rigs and tests.
34 tests. The seven that matter most exercise a real in-process gRPC stack over
TestServer: the unit tests on either side of the wire would both stay green if
the halves disagreed, and gRPC refuses call credentials on a plaintext channel
by default — the UnsafeUseInsecureChannelCallCredentials opt-in is only provable
by making a real call. They confirm correct key passes on unary AND streaming,
wrong key and no-credentials both get PermissionDenied, and an unresolvable key
fails the call with nothing reaching the service.

OPERATIONAL: a site node upgraded to this build without a key will not boot.
That includes the gitignored deploy/wonder-app-vd03/ overlay.

docs/known-issues/2026-07-22-integration-call-routing-is-dead-code.md

@@ -0,0 +1,59 @@
+# Integration call routing (`IntegrationCallRequest`) is dead on both ends
+
+**Date:** 2026-07-22 · **Status:** OPEN (decision needed: wire or delete) · **Severity:** Low (no
+runtime impact — the path cannot be reached) · **Area:** Central–Site Communication
+
+## What
+
+"Pattern 4: Integration Routing" — `CommunicationService.RouteIntegrationCallAsync` →
+`SiteEnvelope(IntegrationCallRequest)` → `SiteCommunicationActor` → an integration handler — is
+plumbed end to end but connected at neither end.
+
+- **No producer.** `RouteIntegrationCallAsync` (`CommunicationService.cs`, "Pattern 4") has **zero
+  callers** in `src/` or `tests/`. It is the only one of `CommunicationService`'s command methods
+  with none.
+- **No handler.** `SiteCommunicationActor` forwards to `_integrationHandler` when one is
+  registered, but `RegisterLocalHandler(LocalHandlerType.Integration, …)` appears **only** in
+  `SiteCommunicationActorTests.cs`. `AkkaHostedService` registers the other three handler types
+  (`Artifacts`, `EventLog`, `ParkedMessages`) and never this one.
+
+So if anything ever did call it, the site would answer
+`IntegrationCallResponse(Success: false, Error: "Integration handler not available")`
+(`SiteCommunicationActor.cs`, Pattern 4) — and the two tests that exercise the path both register
+the handler themselves first, which is why the suite has never noticed.
+
+Do not confuse this with the **Inbound API**'s routed-site-script path, which is live, tested, and
+uses different messages entirely. This is a separate, unused routing pattern that predates it.
+
+## Why it is recorded rather than fixed
+
+Found during the recon for the ClusterClient→gRPC transport migration
+([`docs/plans/2026-07-22-clusterclient-to-grpc-plan.md`](../plans/2026-07-22-clusterclient-to-grpc-plan.md),
+T0.2), which had to enumerate every command crossing the site↔central boundary. Of the **29**
+command types, this is the one that is excluded: **28 migrate to the gRPC contract.**
+
+Porting it would mean designing a proto contract, a `oneof` slot and round-trip mapper tests for a
+verb no caller can invoke and no site can service — and enshrining it on a wire format whose
+evolution rules are additive-only, so an unused RPC slot is permanent. Deleting it during a
+transport migration would mix an unrelated behavioural change into a change whose whole value is
+that behaviour is identical. Hence: excluded from the contract, behaviour untouched, decision
+deferred to its own change.
+
+## Decision needed
+
+Either:
+
+1. **Delete** — remove `RouteIntegrationCallAsync`, the `IntegrationCallRequest`/`Response`
+   messages, the `SiteCommunicationActor` receive block, `LocalHandlerType.Integration`, and the
+   three tests that cover them. This is the default if no consumer is planned.
+2. **Wire** — register a real integration handler on site nodes and give the method a caller. This
+   only makes sense if there is a requirement it serves; none is recorded in
+   `docs/requirements/`.
+
+Whichever is chosen, do it **before Phase 4** of the migration, since Phase 4 deletes the Akka
+transport underneath this path. If it is still dead at that point, option 1 is forced.
+
+## Filing
+
+To be filed as a Gitea issue on `dohertj2/scadabridge` by the repo owner — this note is the
+in-repo record of the finding and of the migration exclusion it justifies.