[WebToolsE2E][Blue] When creating a Razor Page/Razor View file, I encounter the error: "Index1. cshtml appears to not be part of any project..."

[v-reinawang]

REGRESSION INFO: Works on release C#DK 1.41.11[Includes C# 2.87.31]

INSTALL STEPS

1. Repro OS: Win11 24H2 ENU
2. Install latest VSCode (latest released version 1.103.0)
3. Install SDK 10.0 Preview 7/SDK 9.0
4. Install C# prerelease [2.88.42] and C#DK prerelease [1.50.11]

REPRO STEPS

1. Create an ASP.NET Core Empty project
2. Right click the project > New file > Select Razor Page/Razor View> Enter
3. Open OUTPUT window > Select Razor Log

ACTUAL
Will encounter the error:

2025-08-08 02:58:54.254 [error] [Services.IncompatibleProjectNotifier] The Razor editor utilizes the Razor Source Generator. Index1.cshtml appears to not be part of any project, so the source generator is not present and the editing experience will be limited. No more messages will be logged for this scenario.
[Services.IncompatibleProjectNotifier] The Razor editor utilizes the Razor Source Generator. Index1.cshtml appears to not be part of any project, so the source generator is not present and the editing experience will be limited. No more messages will be logged for this scenario.
Stack Trace:
Error: [Services.IncompatibleProjectNotifier] The Razor editor utilizes the Razor Source Generator. Index1.cshtml appears to not be part of any project, so the source generator is not present and the editing experience will be limited. No more messages will be logged for this scenario.
    at RO.log (c:\Users\v-reinawang\.vscode\extensions\ms-dotnettools.csharp-2.88.42\dist\extension.js:1207:18821)
    at c:\Users\v-reinawang\.vscode\extensions\ms-dotnettools.csharp-2.88.42\dist\extension.js:1212:33608
    at mr (c:\Users\v-reinawang\.vscode\extensions\ms-dotnettools.csharp-2.88.42\dist\extension.js:51:1620)
    at Mr (c:\Users\v-reinawang\.vscode\extensions\ms-dotnettools.csharp-2.88.42\dist\extension.js:50:7629)
    at Immediate._onImmediate (c:\Users\v-reinawang\.vscode\extensions\ms-dotnettools.csharp-2.88.42\dist\extension.js:50:7324)
    at processImmediate (node:internal/timers:485:21)

EXPECTED
There should be no errors.

[AbhitejJohn]

Tagging @phil-allen-msft and @davidwengier on this.

[davidwengier]

Suspect this is file-based projects being too enthusiastic, and effectively a dupe of #8480. Will need to repro and see the full debug log to confirm.

[v-reinawang]

Still reproduced in C# main 2.89.17 + C#DK main 1.50.12

[davidwengier]

Okay, I see whats going on. This isn't 100% repro, at least for me, but depends on timing in Roslyn. Previously ending up in Misc Files was a bad thing (thats what dotnet/roslyn#79844 fixed), but now it seems we're just losing a race sometimes, and the document will be in misc files when we get a request, before being moved to the real project. Once that move happens everything is fine, and indeed the Razor editing experience seems to work fine without needing to reopen the document or anything.

The error message is annoying though, as it was designed to tell people why they might get some bad features, but in this case it ends up looking like a bad feature itself, and if we just let it go I suspect nobody would notice.