Spike: Metalama 2026.1 on the .NET 11 RC3 SDK (the RC3 rows of #170) #276

The RC3 part of #170: decision 120's Metalama measurement (RC1, 2026-10-29) repeated on SDK 11.0.100-rc.3.26522.148 with the published 2.3.1 packages: a net11.0 value object built, woven and run; #error version; a declared union; a match on a library's union; LAMA0617 and any new warning; and a direct Metalama.Framework 2027 reference for the C# 15 contrast.

Done when spikes/Sdk11Rc3Metalama/README.md holds the question, the answer and the evidence, KB-060 records the fact, and #170 says the RC3 rows are done. The rest of #170 (the repository on SDK 11, the woven assets compared, the analyzers, NU1605, the license-free CI job, the general availability SDK) stays there.