Phase 3 PR 40 — LiveStackSmokeTests: write-roundtrip + subscribe-receives-OnDataChange against the live Galaxy. Finishes LMX #5 by exercising the IWritable + ISubscribable capability paths end-to-end through the Proxy → OtOpcUaGalaxyHost service → MXAccess → real Galaxy.

Two new facts target DelmiaReceiver_001.TestAttribute — the writable Boolean UDA on the TestMachine_001 hierarchy in this dev Galaxy. The user nominated TestMachine_001 (the deployed test-target object) as a scratch surface for live testing; ZB query showed DelmiaReceiver_001 carries one dynamic_attribute named TestAttribute (mx_data_type=1=Boolean, lock_type=0=writable, security_classification=1=Operate). Naming makes the intent obvious — the attribute exists for exactly this kind of integration testing — and Boolean keeps the assertions simple (invert, write, read back).
Write_then_read_roundtrips_a_writable_Boolean_attribute_on_TestMachine_001: reads the current value as the baseline (Galaxy may return Uncertain quality until the Engine has scanned the attribute at least once — we don't read into a typed bool until Status is Good), inverts it, writes via IWritable, then polls reads in a 5s loop until either the new value comes back or the budget expires. The scan-window poll (rather than a single read after a fixed delay) accommodates Galaxy's variable scan latency on a fresh service start. Restore-on-finally writes the original value back so re-running the test doesn't accumulate a flipped TestAttribute on the dev box (Galaxy holds UDA values across runs since they're deployed). Best-effort restore — swallows exceptions so a failure in restore doesn't mask the primary assertion.
Subscribe_fires_OnDataChange_with_initial_value_then_again_after_a_write: subscribes to the same attribute with a 250ms publishing interval, captures every OnDataChange notification onto a thread-safe ConcurrentQueue (MXAccess advisory fires on its own thread per Galaxy's COM apartment model — must not block it), waits up to 5s for the initial-value callback (per ISubscribable's contract: 'driver MAY fire OnDataChange immediately with the current value'), records the queue depth as a baseline, writes the toggled value, waits up to 8s for at least one MORE notification, then searches the queue tail for the notification carrying the toggled value (initial value may appear multiple times before the write commits — looking at the tail finds the post-write delta even if the queue grew during the wait window). Unsubscribes on finally + restores baseline.
Both tests use Convert.ToBoolean(value ?? false) to defensively handle the Boxed-vs-typed quirk in MessagePack-deserialized Galaxy values — depending on the wire encoding the Boolean might come back as System.Boolean or System.Object boxing one. Convert.ToBoolean handles both. Same pattern in OnReadValue's existing usage.
WaitForAsync helper does the loop+budget pattern shared by both tests.
PR 40 is the code side of LMX #5's final two deferred facts. To actually run them green requires re-executing from a normal (non-admin) PowerShell — the elevated-shell skip from PR 39 fires correctly under bash + sc.exe-context (verified). lmx-followups.md #5 updated to note the new facts + the run command + the one remaining genuine follow-up (alarm-condition fact when an alarm-flagged attribute is deployed on TestMachine_001).
Test posture from elevated bash: 7 LiveStackSmokeTests facts discovered (was 5; +2 new), all skip cleanly with the elevation message. Build clean.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docs/v2/lmx-followups.md

@@ -125,14 +125,29 @@ Shared secret + pipe name resolve from `OTOPCUA_GALAXY_SECRET` /
 `OTOPCUA_GALAXY_PIPE` env vars, falling back to reading the service's
 registry-stored Environment values (requires elevated test host).
 
-**Remaining**:
-- Install + run the `OtOpcUaGalaxyHost` + `OtOpcUa` services on the dev box
-  (`scripts/install/Install-Services.ps1`) so the skip-on-unready tests
-  actually execute and the smoke PR lands green.
-- Subscribe-and-receive-data-change fact (needs a known tag that actually
-  ticks; deferred until operators confirm a scratch tag exists).
-- Write-and-roundtrip fact (needs a test-only UDA or agreed scratch tag
-  so we can't accidentally mutate a process-critical value).
+**PR 40** added the write + subscribe facts targeting
+`DelmiaReceiver_001.TestAttribute` (the writable Boolean UDA the dev Galaxy
+ships under TestMachine_001) — write-then-read with a 5s scan-window poll +
+restore-on-finally, and subscribe-then-write asserting both an initial-value
+OnDataChange and a post-write OnDataChange. PR 39 added the elevated-shell
+short-circuit so a developer running from an admin window gets an actionable
+skip instead of `UnauthorizedAccessException`.
+
+**Run the live tests** (from a NORMAL non-admin PowerShell):
+
+```powershell
+$env:OTOPCUA_GALAXY_SECRET = Get-Content C:\Users\dohertj2\Desktop\lmxopcua\.local\galaxy-host-secret.txt
+cd C:\Users\dohertj2\Desktop\lmxopcua
+dotnet test tests\ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Proxy.Tests --filter "FullyQualifiedName~LiveStackSmokeTests"
+```
+
+Expected: 7/7 pass against the running `OtOpcUaGalaxyHost` service.
+
+**Remaining for #5 in production-grade form**:
+- Confirm the suite passes from a non-elevated shell (operator action).
+- Add similar facts for an alarm-source attribute once `TestMachine_001` (or
+  a sibling) carries a deployed alarm condition — the current dev Galaxy's
+  TestAttribute isn't alarm-flagged.
 
 ## 6. Second driver instance on the same server — **DONE (PR 32)**