MCP Server Stdio transport: configure all logs to go to stderr - #3959
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Pull request overview
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Updates the MCP Server’s stdio transport behavior to avoid tool deserialization issues by ensuring logs are written to stderr instead of stdout.
Changes:
- Configures console logging to route all log levels to stderr via
LogToStandardErrorThreshold. - Minor reordering of
usingdirectives.
marcschier
approved these changes
Jul 6, 2026
Codecov Report✅ All modified and coverable lines are covered by tests. Additional details and impacted files@@ Coverage Diff @@
## master #3959 +/- ##
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- Coverage 76.21% 76.20% -0.01%
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Files 1202 1202
Lines 171601 171601
Branches 29666 29666
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- Hits 130778 130769 -9
- Misses 29778 29794 +16
+ Partials 11045 11038 -7 🚀 New features to boost your workflow:
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marcschier
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Jul 6, 2026
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Please fix the review comments, the ConfigureLogging is probably the better place to conditionally change the logging to stderr (when stdio is configured)
marcschier
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Jul 6, 2026
marcschier
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Jul 6, 2026
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marcschier
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Jul 9, 2026
Brings in 5 upstream commits: OPCFoundation#3957 (expand DI/Fluent API injectability + one-shot ergonomics across client/server/PubSub/discovery/bindings), OPCFoundation#3968 (fix false-positive MODELGEN010), OPCFoundation#3966 (fix source generator dropping BaseAnalogType EURange/EngineeringUnits), OPCFoundation#3949 (Apache Kafka PubSub transport, Part 14 Annex B.2), and OPCFoundation#3959 (MCP server stdio logs to stderr). Resolved one conflict in Directory.Packages.props (three regions), all from our UaLens-specific package entries interleaving with upstream's new Kafka dependency and a Microsoft.Extensions.* version bump: * Kept CommunityToolkit.Mvvm 8.4.2 and added upstream's new Confluent.Kafka 2.15.0. * Accepted upstream's Microsoft.Extensions.* bump (10.0.8 -> 10.0.9, 10.6.0 -> 10.7.0) while re-inserting our Microsoft.Extensions.Diagnostics.ResourceMonitoring 10.5.0 (a UaLens dependency absent from master) in alphabetical position. * Kept ScottPlot.Avalonia 5.1.58 and took upstream's SharpFuzz 2.2.0 -> 2.3.0 bump. UA.slnx auto-merged and retained our McpServer project path. UaLens build clean (0 warnings / 0 errors). Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Description
In the Stdio transport mode of the MCP server, logging is redirected to stderr in order to avoid deserialization exceptions when calling tools
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