RA does not work at all when offline

I tried to do a bit of coding on rustc while on a plane without internet, and noticed that RA handles this situation quite badly. cargo metadata fails because it cannot refresh the index, and then basically nothing works, even though everything needed should be available offline. In particular, not even "check on save" does anything -- I had to run ./x.py check by hand. That worked perfectly fine, demonstrating that RA could also have run x.py as usual and show the diagnostics in the editor.

rust-analyzer version: ad6810e90 2022-06-06 stable

rustc version: rustc 1.63.0-nightly (e09449220 2022-05-31)

relevant settings:

{
    "rust-analyzer.checkOnSave.enable": true,
    "rust-analyzer.checkOnSave.overrideCommand": [
        "./x.py",
        "check",
        "--json-output",
        "library/std",
        "compiler/rustc",
    ],
    "rust-analyzer.rustfmt.overrideCommand": [
        "./build/x86_64-unknown-linux-gnu/stage0/bin/rustfmt",
        "--edition=2021"
    ],
    "rust-analyzer.procMacro.enable": false,
    "editor.formatOnSave": false,
    "files.watcherExclude": {
        "*rustc*/src/llvm-project/**": true,
        "*rustc*/build/**": true,
    },
    "files.exclude": {
        "src/llvm-project/**": true,
        "build/**": true
    },
    "rust-analyzer.cargo.buildScripts.enable": false,
    "rust-analyzer.rustc.source": "./Cargo.toml",
    "rust-analyzer.hover.actions.references.enable": true,
}

Reproduce the offline setup using the listed rust-analyzer settings, especially the ./x.py check override and ./Cargo.toml source, then trace the cargo metadata and check-on-save paths. Confirm the behavior against ./x.py check; done means rust-analyzer can run the configured check command and display diagnostics while offline.