Add managed C# AppMap agent (under managed/)

[evlawler]

What this is

This PR brings the fully managed C# AppMap agent into appmap-dotnet under a new managed/ subdirectory. It's a from-scratch port of the appmap-java architecture — a managed agent that rewrites methods at runtime via Harmony, rather than instrumenting IL from a C++ CLR-profiler plugin.

The motivation (vs. the existing C++ prototype): being fully managed makes it cross-platform (not Linux-only) and considerably easier to evolve, while emitting the same AppMap JSON (format v1.2) as appmap-java.

Layout

Everything lands under managed/ — the existing C++ prototype and its CI are untouched, so the two implementations sit side by side for comparison. (The agent's own CI workflows are at managed/.github/workflows/ and therefore do not auto-run in this repo.)

Project	Role
managed/src/AppMap.Agent	Config, recorder, event model, serializer, Harmony instrumentation, SQL + built-in hooks
managed/src/AppMap.Attributes	[Labels] attribute for application code
managed/src/AppMap.StartupHook	DOTNET_STARTUP_HOOKS entry point
managed/src/AppMap.AspNetCore	HTTP server events, request + remote recording
managed/src/AppMap.SystemWeb	The same for classic ASP.NET (.NET Framework)
managed/src/AppMap.Testing.{Xunit,NUnit}	One AppMap per test
managed/test/AppMap.Agent.Tests	Serializer / config / value-capture unit tests
managed/examples/{HelloAppMap,PetClinic}	Smallest recorded app; ASP.NET Core + EF Core web app (HTTP + SQL)
managed/harness/	Records an unmodified real app (eShopOnWeb) and CLI-validates the maps

See managed/README.md for build/usage and managed/DESIGN.md for the design.

Status

Draft, opened for @dividedmind to review the approach. Imported as-is from the prototyping repo; happy to reshape placement, naming, or split it up based on feedback.

[evlawler]

@dividedmind — when you have a moment, could you take an early look at the approach here? Keeping it as a draft on purpose: this is a gut-check on direction, not a final PR.

The short version: a fully managed C# AppMap agent (Harmony-based runtime rewriting, porting the appmap-java architecture) landed under managed/, alongside the existing C++ prototype — nothing in the C++ path or its CI is touched. Motivation is cross-platform support and easier evolution vs. the CLR-profiler plugin, emitting the same AppMap JSON as appmap-java.

Mainly looking for feedback on placement/naming and whether this direction is worth pursuing. Happy to reshape or split it up. See the PR description, managed/README.md, and managed/DESIGN.md for details. Thanks!

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