docs(secrets): OtOpcUa adoption executed + merged (lmxopcua @872cf7e3) — all 4 apps done

Record the OtOpcUa secrets adoption (G-2/G-4/G-5/G-6, the last app): FF-merged +
pushed to lmxopcua origin/master @872cf7e3. Update the components/secrets/GAPS.md
OtOpcUa bullet (execution record + the three verified plan deviations + the regression
the gate caught) and the CLAUDE.md secrets-component-table row. All four apps
(HistorianGateway, mxaccessgw, ScadaBridge, OtOpcUa) now adopt ZB.MOM.WW.Secrets.

components/secrets/GAPS.md

@@ -37,8 +37,8 @@ construction).
   pre-host expander migrates the store unconditionally every Central boot). One review-flagged non-blocking
   follow-up: a pre-existing xUnit env-mutation CI-flake that T4 amplifies (single `[Collection]` / disable
   parallelization for Host.Tests).
-- **OtOpcUa — planned, NOT executed (the LAST remaining app; recommended next — carries the highest-value G-2 Layer-B driver secrets).**
-  **Plan re-verified 2026-07-16 against `origin/master` @ `ec6598ce`** (the merged **v3.0 dual-namespace** rewrite, PR #472). The v3.0 rewrite did NOT touch the driver-secret flow, so the approach holds; the plan was corrected for: OtOpcUa **is** on Central Package Management (was mis-stated as inline-versioned), `OpcUaClientDriverOptions` lives in `…Driver.OpcUaClient.Contracts` + `GalaxyDriverBrowser` in `…Driver.Galaxy.Browser`, and `DriverHostActor.cs` line shifts (1704/1756/1790 → 1766/1818/1852). Program.cs / Security / AdminUI anchors survived essentially unchanged.
+- **OtOpcUa — G-2 + G-4 + G-5 + G-6 DONE (the LAST app — all three now adopted).** Executed 2026-07-16 via the plan below (10 tasks, 2 slices, subagent-driven, classification-driven reviews), **FF-merged + pushed to `origin/master` (lmxopcua @ `872cf7e3`, `ec6598ce..872cf7e3`)**. Clean build (0 errors). The full offline suite caught **one real regression** — `AddOtOpcUaDriverFactories`' registration now resolves `ISecretResolver` (Galaxy/OpcUaClient secret: refs), so two `ResilienceInvokerFactoryRegistrationTests` that built a minimal container threw `No service for ISecretResolver`; fixed test-only by registering a stub resolver (production always has it via the unconditional `AddZbSecrets`, and `GetRequiredService` correctly fails-fast for a genuinely misconfigured host). Touched-area suites green (Galaxy 338, OpcUaClient 142, AdminUI 662); remaining non-passes are unrelated (flaky Akka/Roslyn timing tests pass in isolation; the environmental `AbCip_Green_AgainstSim` sim-fixture test — zero AbCip code touched). **Three deliberate deviations from the plan's literal text** (verified corrections, same class as the CPM miss the plan itself caught): (1) **G-4 does NOT commit a `${secret:}` token into the default appsettings** — the expander is fail-closed AND section-agnostic and the only committed secret-shaped value is `ServerHistorian:ApiKey=""` (empty, disabled-by-default), so a committed token would break every dev/CI/`TwoNodeClusterHarness` boot for zero at-rest benefit; instead documented the token-delivery convention (`docs/security.md`) + updated the ServerHistorian comments, and proved fail-closed live (unseeded → `SecretNotFoundException` at pre-host expansion; seeded → resolves). (2) **G-5 shipped docs-only** (`docs/operations/2026-07-16-secrets-clustered-master-key.md`) — hardcoding `Source=File`+shared paths into the committed role-overlay appsettings (also consumed by dev + integration) would break those boots; base stays `Source=Environment`. Mirrors the ScadaBridge G-5 resolution. (3) **Task 8 resolves in the factory/driver only, NOT the probe** — the v3 `OpcUaClientDriverProbe` is unauthenticated `GetEndpoints`-only and never reads `Password`/`UserCertificatePassword`, so probe resolution would be dead code. Layer-B resolution mirrors Galaxy: the sync driver-registry factory means resolution happens lazily at the driver's async session-open (`GalaxyDriver.BuildClientOptionsAsync` / `OpcUaClientDriver.InitializeAsync`), threaded via ctor + `DriverFactoryBootstrap` (real resolver from DI; `NullSecretResolver` null-object backs test/parse paths only, fail-closed on `secret:`). `OpcUaClientDriverOptions` was converted `sealed class` → `sealed record` for the `with`-expression (no positional params → identical JSON; verified no reference-equality/dict-key/ToString-log usages → no leak/behavior change). AdminUI G-2c is structurally leak-proof: `DriverConfig` persists as an opaque JSON string via `RawTreeService`, which has NO resolver dependency. **Live wonder gate deferred to rollout** (needs the shared KEK + a seeded real gateway key on the box — same as HistorianGateway/ScadaBridge were proven). **All of G-2/G-4/G-5/G-6 now DONE across all three apps + mxaccessgw.**
+  **Plan re-verified 2026-07-16 against `origin/master` @ `ec6598ce`** (the merged **v3.0 dual-namespace** rewrite, PR #472). The v3.0 rewrite did NOT touch the driver-secret flow, so the approach held; the plan was corrected for: OtOpcUa **is** on Central Package Management (was mis-stated as inline-versioned), `OpcUaClientDriverOptions` lives in `…Driver.OpcUaClient.Contracts` + `GalaxyDriverBrowser` in `…Driver.Galaxy.Browser`, and `DriverHostActor.cs` line shifts (1704/1756/1790 → 1766/1818/1852). Program.cs / Security / AdminUI anchors survived essentially unchanged.
 
 ## Design + implementation plans (2026-07-16)