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2026-10-11 csharp dotnet

How to tail a log file in C# while another process is still writing to it

Open the log with FileShare.ReadWrite | FileShare.Delete, seek to the end, poll for new bytes, decode them with your own UTF-8 Decoder instead of StreamReader, and handle truncation and rotation explicitly. A tested tail -F implementation for .NET 10 and .NET 11.

2026-10-26 dotnet csharp

How to use a different Serilog output template per log level from appsettings.json

outputTemplate is fixed per sink, so per-level formatting needs either an ExpressionTemplate with {#if @l ...} blocks or two Logger sub-loggers with ByIncludingOnly / ByExcluding filters. Both configured purely from appsettings.json, tested on Serilog 4.4, Serilog.Settings.Configuration 10.0.1 and Serilog.Expressions 5.0.

2026-10-04 dotnet dotnet-10

How to detect Windows session lock, unlock, logon and logoff events in a C# app

Use SystemEvents.SessionSwitch in a desktop or console app, override OnSessionChange in a Windows service, or hook WM_WTSSESSION_CHANGE yourself. Covers .NET 10 code for all three, the hidden '.NET System Events' thread, why services see logon but desktop apps do not, out-of-order notifications, and how to query the current lock state with WTSQuerySessionInformation.

2026-11-07 dotnet github-copilot arm64

Copilot's Upgrade Agent Now Migrates .NET Apps to Windows Arm64: What It Is Actually Looking For

On November 5, 2026 Microsoft added a Windows Arm64 migration scenario to the GitHub Copilot upgrade agent. Here is what the blockers look like in a real .NET project, what the agent can and cannot verify, and how to check the result yourself.

2026-11-07 errors dotnet csharp

Fix: Collection was modified; enumeration operation may not execute in C#

You changed a List or Dictionary while a foreach was walking it. Iterate a copy, use RemoveAll, loop backwards with for, or lock both sides. Which mutations throw on .NET 10 and 11, and why Dictionary.Remove does not.

2026-11-07 github-copilot llm ai-agents

What Is GitHub Copilot Fusion and Which Effort Level Should You Pick?

Copilot Fusion, generally available since October 28, 2026, is a runtime model router that picks a model and an execution pattern (Single, Cascade, or Critique) per prompt. Here is how the three patterns work, what Fusion Standard, High, and Max cost you in AI credits, how to lock the effort level with managed-settings.json, and the gotchas the docs bury.

2026-11-07 dotnet csharp dotnet-11

Why does a C# decimal keep trailing zeros, and how do I remove them?

1.10m prints "1.10" because System.Decimal stores a scale alongside its digits, and arithmetic, parsing, and JSON all preserve it. How the scale is chosen, why 1.1m == 1.10m but their strings differ, three ways to strip trailing zeros (G29, a 0.## pattern, dividing by 1.000...m) and the 1E-05 trap in G29, how to force a fixed scale, and why .NET 11's double to decimal change produces digits no trick removes. Verified on .NET 10.0.14 and .NET 11 RC3.

2026-11-06 ai-agents mcp agent-client-protocol

ACP vs MCP: What the Agent Client Protocol Does That MCP Doesn't

ACP (Agent Client Protocol, v1) connects an editor to a coding agent; MCP (spec 2026-07-28) connects an agent to tools. They sit on opposite sides of the agent and are used together: ACP's session/new even carries the MCP servers the agent should start. Here is the feature matrix, the wire flow, and a working agent and client checked against @agentclientprotocol/sdk 2.4.0.

2026-11-06 automapper dotnet security

AutoMapper 16.3 and 15.1.4: MaxDepth Did Not Protect Records, Derived Maps, or Dictionary Sources

AutoMapper 16.3.0 and 15.1.4 fix two high-severity advisories where deeply nested input bypassed MaxDepth and crashed the process with an uncatchable StackOverflowException. Here is which mapping paths were exposed and what changes when you upgrade.

2026-11-06 dotnet csharp linq

Is List<T>.Sort stable in C#? Why equal elements change order

List<T>.Sort, Array.Sort, Span<T>.Sort and ImmutableArray.Sort are unstable introsorts, so items with equal keys can swap places. Enumerable.OrderBy is stable. Measured on .NET 10: why lists of 16 or fewer items look stable, why three items are not, how to get a stable in-place sort, and what it costs.

2026-11-06 dotnet csharp dotnet-11

Why does Math.Round(2.5) return 2 in C#?

Math.Round uses banker's rounding (MidpointRounding.ToEven) by default, so 2.5 rounds to 2 and 3.5 rounds to 4. How to get 'school' rounding with AwayFromZero, why Math.Round(2.675, 2) still gives 2.67, how .NET 11 changed Math.Round(double, digits) to round the exact binary value, and why ToString("F2") disagrees with decimal formatting. Verified on .NET 10.0.14 and .NET 11 RC3.

2026-11-06 dotnet csharp dotnet-10

Why does string.GetHashCode() return a different value every run in .NET?

Since .NET Core, string.GetHashCode() is seeded with a random per-process value (Marvin hashing), so the same string hashes differently in every process. Why the runtime does it, which types are affected (HashCode.Combine, ValueTuple, records with string members), how Dictionary<string, T> quietly avoids the cost, and how to get a stable hash with XxHash3 or FNV-1a, verified on .NET 10.0.10.

2026-11-05 github-actions ci security

GitHub Actions blocks pull_request_target by default on December 2: what public .NET repos must check

Starting December 2, 2026, GitHub Actions blocks pull_request_target events in all public repositories unless an Actions event policy allows them. Brownouts hit on November 9 and 16. Here is how to find affected workflows and either migrate to pull_request or opt back in.

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