New files are not picked up by the roslyn language server

[sse-virto]

Description

Files created after the C# language server (csharp, Roslyn) has loaded its projects never join the project's compilation. get_diagnostics_for_file then reports phantom errors for the whole session:

• Files referencing a type defined in a new file: CS0246 The type or namespace name 'X' could not be found, CS0103
• The new file itself: IDE0005 Using directive is unnecessary on usings that are required
• dotnet build --no-incremental on the same project: Build succeeded, 0 errors

Hints

It seems the new file is opened as a Miscellaneous Files document — compiled standalone against a bare reference set — so nothing in it resolves and its usings look unused, while the rest of the project cannot see its types.

Reproduction

1. Start Serena on a C# project and let the language server finish indexing.
2. Move a type out of an existing file into a new file in the same project (any way of creating a .cs file works).
3. Call get_diagnostics_for_file on the original file and on the new file.

Observed: CS0246/CS0103 on the original file, IDE0005 on the new file's required usings.
Expected: the diagnostics dotnet build produces — none.

Analysis

File watching does reach the server: sync_file_system_changes logs
File system polling complete; 3 change events sent to language servers. Content sync of pre-existing files works.
It seems Roslyn adds documents when it re-evaluates a project, not on a watched-file Created event.

Related

#1593 (find_symbol can return stale/incorrect information, observed for Clojure/LSP)

Seems similar issue but unrelated fix.

Preconditions:

• [x ] I have made sure it's an actual issue, not a question (use GitHub Discussions instead).
• [x ] I have consulted the user guide and verified that the issue cannot be resolved by adjusting configuration/following recommended workflows.
• [x ] I have looked for similar issues and discussions, including closed ones.

Issue details:

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• [ x] I have explained how the issue arose and, where possible, added instructions on how to reproduce it.
• [ x] I have added details on my setup: Serena version, MCP client, OS, the programming language(s), relevant configuration adjustments and project specifics.
• [ x] If the issue relates to an application of Serena to an open-source project, I have added the link.