There are plenty of crashes to work through here, will need to spend some time doing so.

* upstream/main: (31 commits)
  Remove bogus xlf tag (dotnet#80357)
  Fix missing type argument checks
  Add tests
  Use dotnet run file for generating compiler code (dotnet#80248)
  Only restore based on assets file changes if the actual content changed (dotnet#80341)
  make expressionbody analyzer use semanticspananalysis (dotnet#80339)
  [EnC] Use ignoreAssemblyKey: false to resolve symbol keys (dotnet#80342)
  Properly populate ExportedType metadata table in presence of extension block. (dotnet#80311)
  Propagate `params` to lambdas and local functions (dotnet#79880)
  Change 17.15 to VS 2026 preview. (dotnet#80325)
  Improve virtualproject support for older .NET SDKs (dotnet#80324)
  Update dependencies from https://github.com/dotnet/dotnet build 283666 (dotnet#80344)
  Update dependencies from https://github.com/dotnet/arcade build 20250917.6 (dotnet#80343)
  Simplifying
  Fix tests
  Fix tests
  Fix introduce variable placement in top level statements
  move to immutable types in signature help
  move to immutable types in signature help
  Fix check
  ...

* upstream/main: (332 commits)
  Cache lambdas in analyzer driver (dotnet#80759)
  Add information for NuGet package version 4.14 (dotnet#80870)
  Add missing search keywords to VB Advanced options page
  Fix IDE0031 false positive when preprocessor directives are used in if statements (dotnet#80878)
  Use core compiler on netfx hosts with toolset package (dotnet#80631)
  Make string concat assert more precise (dotnet#80619)
  Extensions: address some diagnostic quality issues (dotnet#80827)
  Add note on traversal order for bound nodes (dotnet#80872)
  Ensure that locals at the top level of a constructor have the same safe-context as parameters (dotnet#80807)
  Fix handling of SymbolDisplayCompilerInternalOptions.UseArityForGenericTypes option for non-native symbol implementations (dotnet#80826)
  Update src/Analyzers/CSharp/Tests/UseCollectionInitializer/UseCollectionInitializerTests.cs
  Add IsValidContainingStatement check to prevent collection initializers in using declarations
  Add back old DocumentSpan constructor (dotnet#80864)
  Add tests verifying pointer types in type parameters require unsafe context (dotnet#80776)
  Add regression test for Interlocked.Exchange with nullable types (dotnet#80796)
  Add regression test for ParseAttributeArgumentList with invalid input (fixes dotnet#8699) (dotnet#80705)
  Add regression test for compiler crash with syntax error in indexer declaration (dotnet#80772)
  Add runtime NullReferenceException validation to foreach null iteration tests (dotnet#80839)
  Update MicrosoftBuildTasksCoreVersionForMetrics to 17.11.48 (dotnet#80812)
  Mark CS4009 error as a "build only" error. (dotnet#80698)
  ...