perry check --check-deps false positive: "compilation is guaranteed to succeed" despite unsupported codegen expressions

[proggeramlug]

Environment

• perry 0.5.92
• macOS arm64 (darwin 25.4.0)

Problem

perry check --check-deps <file> reports

All checks passed! - N file(s) checked
[OK] Compilation is guaranteed to succeed

but running perry compile on the same file immediately afterwards fails with perry-codegen Phase 2: expression ... not yet supported (see #78). The dependency-check claim is wrong: compilation is not guaranteed.

This breaks CI. Any pipeline that gates on perry check --check-deps passing will happily promote broken code.

Reproduction

Using the minimal repro from #78:

// minrepro.ts
function describe(v: unknown): string {
    if (Buffer.isBuffer(v)) {
        return 'buffer of length ' + v.length;
    }
    return typeof v;
}

$ perry check --check-deps minrepro.ts
Checking 1 file(s)...
Dependency checking enabled.

All checks passed! - 1 file(s) checked

[OK] Compilation is guaranteed to succeed

$ perry compile minrepro.ts -o /tmp/minrepro
# → Error compiling module 'minrepro.ts': lowering function 'describe':
#   perry-codegen Phase 2: expression BufferIsBuffer not yet supported
# → ld: error: linker command failed ...

Expected

Either:

• check runs the codegen-lowering pass and reports unsupported expressions as hard failures, OR
• the text softens to "Compilation may succeed" / "Type compatibility OK — codegen not verified".

Anything but "guaranteed to succeed" when it demonstrably does not.

Hit in real code

@perry/mysql's perry check --check-deps passed cleanly across all 60 modules; actual perry compile immediately hit #78. Spent ~20 min chasing link errors before realising the check was the wrong scope.

[proggeramlug]

Fixed in v0.5.95 (commit 962080f). See CLAUDE.md v0.5.95 entry for the bundle changelog covering #78–#82.