docs(grpc): Phase 0 live gate PASS — record results, the inert-gate defect, and the trap for phases 1A/1B

The gate's first run failed on a defect the green suite could not see: two public
constructors on ControlPlaneAuthInterceptor made Grpc.AspNetCore's activation
throw per call, so correct key, wrong key and no key all produced identical
errors. Recorded in full because the symptom (Unknown / "Exception was thrown by
handler") points at the handler, not at auth, and because phases 1A/1B both add
services to this same interceptor — they must extend DefaultGatedPrefixes rather
than add a second public constructor.

Also records what the gate does NOT cover: live streaming under load, key
rotation on a running pair, and docker-env2 (keyed but neither redeployed nor
gated).

docs/plans/2026-07-22-clusterclient-to-grpc-live-gate.md

@@ -0,0 +1,98 @@
+# ClusterClient → gRPC migration — live gate results
+
+Rig: `docker/` (2 central + 3×2 site + traefik), rebuilt from the branch under test via
+`bash docker/deploy.sh`. Recorded check-by-check in the family's live-gate format. Phase 5's
+full eight-check gate is recorded further down as those phases land; this file starts with
+Phase 0, whose DoD has its own smaller gate.
+
+---
+
+## Phase 0 — PSK auth + dead-code removal — **PASS** (2026-07-22)
+
+Branch `feat/grpc-phase0-psk` @ `228ff8b4`. Image rebuilt, all 9 containers recreated.
+
+### Baseline (pre-change build, same rig)
+
+An unauthenticated call from the host to a site's audit-pull RPC was **accepted**:
+
+```
+$ grpcurl -plaintext -d '{"batch_size":1}' localhost:9023 sitestream.SiteStreamService/PullAuditEvents
+{}
+```
+
+That is the gap Phase 0 closes, reproduced rather than assumed.
+
+### Checks
+
+| # | Check | Result |
+|---|---|---|
+| 1 | All 8 nodes boot with keys configured (new `StartupValidator` rule) | **PASS** — all recreated and reached ready |
+| 2 | Unauthenticated `PullAuditEvents` ⇒ `PermissionDenied`, all 3 sites | **PASS** |
+| 3 | Wrong key (site-b's key presented to site-a) ⇒ `PermissionDenied` | **PASS** — per-site scoping is real, not decorative |
+| 4 | Correct key ⇒ success, all 3 sites | **PASS** |
+| 5 | Central's own authenticated paths still work | **PASS** — 14 successful `PullAuditEvents` from central to site-a; **0** auth failures in either central's log |
+| 6 | LocalDb sync unaffected by the new interceptor | **PASS** — **0** control-plane rejections and **0** sync auth failures on the passive peer; session connected after one boot-order retry |
+| 7 | No interceptor-activation errors | **PASS** — 0 (see the defect below) |
+
+Evidence for 2–4:
+
+```
+=== NO CREDENTIALS ===
+  :9023 -> ERROR: Code: PermissionDenied  Message: Control plane authentication failed.
+  :9033 -> ERROR: Code: PermissionDenied  Message: Control plane authentication failed.
+  :9043 -> ERROR: Code: PermissionDenied  Message: Control plane authentication failed.
+
+=== WRONG KEY (site-b's key against site-a) ===
+  :9023 -> ERROR: Code: PermissionDenied  Message: Control plane authentication failed.
+
+=== CORRECT KEY ===
+  site-a :9023 -> {}
+  site-b :9033 -> {}
+  site-c :9043 -> {}
+```
+
+Site-a rejected exactly **2** calls — the two deliberate probes above — and nothing else.
+
+### Defect the gate caught that the test suite did not
+
+**First run of this gate FAILED**, and is worth recording because the failure mode is
+deceptive.
+
+`Grpc.AspNetCore` activates a type-registered interceptor through
+`InterceptorRegistration.GetFactory()`, which throws when more than one public constructor is
+applicable. `ControlPlaneAuthInterceptor` shipped with two — the DI one and a prefix-set
+overload intended for later phases.
+
+The throw happens **inside the pipeline, per call**, so:
+
+- nothing failed at startup; the node booted, joined its pair and reported healthy;
+- every gated call died with `Unknown / "Exception was thrown by handler"`, which reads as a
+  handler bug rather than an auth bug;
+- **correct key, wrong key and no key produced identical errors** — the tell. A gate that
+  cannot distinguish those is not authenticating anything.
+
+Site-a's log at the time: three `PullAuditEvents` calls, three identical
+`System.InvalidOperationException: Multiple constructors accepting all given argument types
+have been found in type 'ControlPlaneAuthInterceptor'`.
+
+The full suite was green when this shipped — **29 suites, 6,872 tests, 0 failures**. The
+in-process end-to-end test missed it because it registered the interceptor with
+`AddSingleton` alongside `AddGrpc`, so DI returned the instance and gRPC's activation path
+never ran.
+
+Fixed in `228ff8b4`: the prefix-set constructor is `internal`; the end-to-end harness now
+registers exactly as `Program.cs` does (by type, not in DI); and a reflection assertion pins
+"exactly one public constructor", since that is the actual invariant.
+
+**Lesson for phases 1A/1B, which both add services to this interceptor:** extend
+`DefaultGatedPrefixes`; do not add a second public constructor. And any in-process harness for
+a DI-activated component must mirror the production registration shape or it proves less than
+it appears to.
+
+### Not covered by this gate
+
+- Streaming subscriptions were exercised in-process (TestServer), not over the rig. The
+  interceptor is path-scoped, not method-scoped, so the rig's `PullAuditEvents` evidence covers
+  the same code path — but a live `SubscribeInstance` under load is untested here.
+- Key **rotation** on a live pair.
+- `docker-env2` was updated with its own key but not redeployed or gated.

docs/plans/2026-07-22-clusterclient-to-grpc-plan.md.tasks.json

@@ -81,7 +81,7 @@
         "T0.3",
         "T0.4"
       ],
-      "notes": "Rig half needs user approval (docker/deploy.sh recreates 8 containers)."
+      "notes": "Live gate PASS 2026-07-22 (docs/plans/2026-07-22-clusterclient-to-grpc-live-gate.md). Suite: 29 non-Playwright suites / 6872 tests / 0 failures; Host.Tests 366. Playwright re-run against the stable rig was still in flight at compaction \u2014 the earlier 44 failures were contaminated by a concurrent rig rebuild and are VOID. REMAINING: confirm Playwright, then PR + merge (held for the user per the plan's stop-at-DoD rule)."
     },
     {
       "id": "T1A.1",