Flycheck diagnostics should be triggered by changes to the project files that were not triggered by the client

Rust Analyzer does not seem to trigger flycheck without user saving (even if the state of the files on disk did change), which leads to stale rustc diagnostics.

rust-analyzer version:

rust-analyzer version: 0.3.2896-standalone (e266f5cab8 2026-05-10) [/Users/hiro/.vscode/extensions/rust-lang.rust-analyzer-0.3.2896-darwin-arm64/server/rust-analyzer]

rustc version: rustc 1.95.0 (59807616e 2026-04-14)

editor or extension: VSC and Zed (I don't believe version is relevant here)

relevant settings: N/A

code snippet to reproduce:
Start with following code in git repo (committed):

fn food() {}
fn main() {
  food();
}

Introduce an error and save (without committing):

fn food() {}
fn main() {
  food(1);
}

Result: 2 diagnostics ✅
Now, run a git restore .:

fn food() {}
fn main() {
  food();
}

Result: 1 outstanding rustc diagnostic ❌
Expected result: No diagnostics

In this scenario, RA does not witness any didSaves after git restore which means that flycheck is never triggered. However, it could trigger it after a brief debounce or what have you.

Start by tracing how external project-file changes are observed and how those changes trigger flycheck in rust-analyzer. Reproduce the git restore scenario, then verify that restoring the committed Rust source causes the stale rustc diagnostic to disappear without a client save.