textfieldGetString return value corrupted when stored in local variable #10

Bug Description

textfieldGetString() returns a NaN-boxed string correctly at the native level (verified via Rust debug prints), but the value becomes undefined when used from TypeScript.

Root Cause Analysis

The Rust get_string_value() function correctly reads the NSTextField value and returns it via js_string_from_bytes + js_nanbox_string. The NaN-boxed f64 is valid.

However, when the result is stored in a const variable that the codegen marks as is_string, the codegen:

1. Extracts the raw i64 pointer from the NaN-box (since is_string locals are stored as i64)
2. Later, when the variable is passed to encodeURIComponent() or used in ||, the i64 is not re-NaN-boxed

This causes:

• || operator: js_is_truthy receives the raw i64 interpreted as f64, which is NaN → always falsy
• encodeURIComponent(): receives garbage value → produces "undefined"

Reproduction

import { TextField, textfieldGetString } from 'perry/ui';

const field = TextField('', (val: string) => {});
// User types "hello" in the field

const btn = Button('Test', () => {
  const raw = textfieldGetString(field);
  // raw.length works (inline string length access on i64 pointer)
  // typeof raw === 'string' works (compile-time constant)
  // But encodeURIComponent(raw) produces "undefined"
  // And (raw || 'fallback') always returns 'fallback'
});

Observations

• name/host/port fields work because their variables are used in string concatenation (+) which the codegen handles with string-aware code
• user/pass fields fail because they're passed to encodeURIComponent() which expects f64 NaN-boxed values
• The typeof x === 'string' && x.length > 0 check passes (both are inlined by codegen) but the VALUE is still corrupted when used as an argument to other functions
• Pinning the GC allocation doesn't help — the string data is intact, but the NaN-boxing is stripped

Expected Fix

When an is_string local (stored as i64) is passed to a generic function that expects f64, the codegen should re-NaN-box it via js_nanbox_string(ptr).