068 phantom obligation on primitive string

// Test: phantom obligation on a primitive string composes with sanitization.
//
// The phantom checker treats `[]const u8<unsanitized!>` exactly as it treats
// `*File<opened!>` — a value with a tracked obligation that must be
// discharged by an event accepting `<!unsanitized>`. This is taint tracking
// on top of the same machinery that handles units of measure and resource
// lifecycle, with no checker-side additions.
//
// Positive case: produce-then-sanitize-then-use compiles + runs cleanly.
// Negative twin: 330_069 (skip the sanitize, get rejected at compile time).

~import std/io

~pub event get-input {}
| line []const u8<unsanitized!>

~get-input => line "user input data"

~event sanitize { input: []const u8<!unsanitized> }
| clean []const u8

~sanitize => clean input

~get-input()
| line s |> sanitize(input: s)
    | clean c |> std/io:print.ln(c)