Added MxGateway.Worker.Tests/AlarmClientWmProbeTests.cs as a Skip-gated
runtime probe. Run on the dev rig 2026-05-01 against the live AVEVA
install (Galaxy reachable, no manual alarm fired). Findings:
- RegisterConsumer(hWnd, ...) and Subscribe("\Galaxy!", ...) both
return 0 (success). Calls are valid against the deployed assembly.
- A registered-message-class WM (ID 0xC275 in this OS session) fires
every ~1 second after Subscribe completes. Constant wParam=0x1100,
constant lParam=0x079E46D8 — looks like a heartbeat / keepalive,
not a per-change notification.
- Critically, this WM is delivered to AVEVA's own internal window
(hwnd=0x18032E), NOT to the consumer hWnd we registered. The
consumer window receives only the standard WM_CREATE / WM_DESTROY
sequence; no AVEVA traffic in between.
This invalidates the WM_APP-pump design previously documented. The
hWnd parameter to RegisterConsumer appears to be a registration
identity only — AVEVA's notification path runs entirely against
AVEVA's own internal window.
Two viable A.2 designs replace the previous one:
1. Polling. Call GetStatistics on a 500ms timer in the worker's STA
and react to whatever change set it reports. No window plumbing
needed. Latency floor = poll period. Matches AVEVA's own
internal heartbeat cadence.
2. Hook AVEVA's internal window. Discover AVEVA's own hwnd,
SetWindowSubclass on it, intercept WM 0xC275 on AVEVA's thread.
Higher fidelity, lower latency, but invasive and fragile across
AVEVA upgrades — likely a non-starter.
Recommendation in docs/AlarmClientDiscovery.md is option 1 (polling)
unless a follow-up probe with a real fired alarm shows AVEVA does
post change-specific WMs to a different hWnd.
Open follow-up probes documented:
- Fire a real Galaxy alarm during pump and check whether WM 0xC275
cadence changes or GetStatistics returns non-empty arrays.
- GetStatistics threading affinity test.
- Hook AVEVA's internal window 0x18032E.
- Decompile aaAlarmManagedClient IL for RegisterConsumer to find
whether WNAL_Register's callback surface is wrapped.
Test project changes:
- Added Reference to aaAlarmManagedClient + IAlarmMgrDataProvider
(Private=true so the DLL gets copied into bin for test load).
- Test-suite-wide: 127 real tests still pass; both alarm-related
Skip-gated tests skip cleanly.
Code change to the probe is additive — the worker is unchanged.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Joseph Doherty
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