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mbproxy: fix the dashboard's C2/M-series review findings

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Closes the on-demand-capture leak cluster from the code review. The capture's armed state was driven off SignalR's ConnectionId, which changes on every transport reconnect, so a reconnect-during-view leaked a subscriber and left the capture armed forever with no viewer. PlcSubscriptionTracker now keys on a stable per-page-load tabId, and StatusBroadcaster reconciles capture arm state from the live viewer set each push cycle — making arming single-threaded and reconnect-safe. Also fixes the TagValueCapture disarm-vs-record race, the bind-failure broadcaster/listener leak, removes dead JSON-context code, and reworks the frontend cold-start retry plus an unknown-PLC watchdog. Adds tracker / broadcaster-loop / race / wire-shape test coverage.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
This commit is contained in:
Joseph Doherty
2026-05-16 16:12:43 -04:00
parent 554b05d28c
commit 374eecd205
16 changed files with 580 additions and 212 deletions
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mbproxy/docs/Operations/StatusPage.md
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@@ -312,7 +312,7 @@ The UI is a Bootstrap 5 single-page app served from embedded assets under `src/M
## Debug View Data
The detail page's debug view is fed by an **on-demand per-tag value capture** (`Proxy/TagValueCapture.cs`, one per PLC, held in `Proxy/TagCaptureRegistry.cs`). The `BcdPduPipeline` records the last raw/decoded value for each configured BCD tag — but only while the capture is *armed*. `StatusHub` arms a PLC's capture when the first detail page subscribes and disarms it (clearing all slots) when the last viewer leaves, so the hot path carries zero cost when nobody is watching. The per-PLC payload is `PlcDetailResponse` (`src/Mbproxy/Admin/DebugDto.cs`):
The detail page's debug view is fed by an **on-demand per-tag value capture** (`Proxy/TagValueCapture.cs`, one per PLC, held in `Proxy/TagCaptureRegistry.cs`). The `BcdPduPipeline` records the last raw/decoded value for each configured BCD tag — but only while the capture is *armed*. `StatusBroadcaster` reconciles arm state every push cycle from `PlcSubscriptionTracker`: a PLC's capture is armed exactly while at least one detail-page browser tab is open, and disarmed (clearing all slots) otherwise — so the hot path carries zero cost when nobody is watching. The tracker keys on a stable per-page-load tab id, not the SignalR `ConnectionId`, so a transport reconnect cannot leak an armed capture. The per-PLC payload is `PlcDetailResponse` (`src/Mbproxy/Admin/DebugDto.cs`):
> When the response cache is enabled, an FC03/FC04 **cache hit** bypasses the pipeline. To keep the debug view live for cached tags, each cache entry carries the tag observations captured when it was stored (only when a viewer was armed at that time); a hit replays them into the capture, re-stamped to the hit time. The debug view therefore reflects the value the client actually receives — cache-served reads included — not only backend round-trips.