Fix: "skipping diagnostics update, no worktree found” / “URI is not a file" errors in Zed

[0xpantera]

What Cairo-LS emits

• Cairo-LS doesn’t limit itself to the files that are in the user’s project directory.
• During analysis it also walks std-lib sources (downloaded into Scarb’s cache) and crate-dependencies pulled from registry/src/....
• For every file it analyses it may publish diagnostics:

{
  "method": "textDocument/publishDiagnostics",
  "params": {
    "uri": "file:///Users/…/Library/Caches/com.swmansion.scarb/registry/std/v2.11.4/core/src/panics.cairo",
    "diagnostics": [ … ]
  }
}

or, when the file is kept only in memory, using Cairo-LS’s virtual-file-system URIs:
vfs://1234/embeddable.cairo

How current Zed reacts

Zed’s LSP layer assumes that every URI it gets back:
1. either points to a real file inside the work-tree that the user opened, or
2. is one of its own in-memory buffers.

If the URI fails both checks Zed logs:

WARN  skipping diagnostics update, no worktree found for path …
ERROR URI is not a file

and simply discards the diagnostics.
Nothing is actually broken, the warnings only mean “I’m ignoring that diagnostic because I don’t know where to show it”.

I couldn't find if Zed allows extensions to register external / virtual files and surface their diagnostics in secondary panels (much like VS Code does).