number + typedArray[oob] yields undefined instead of NaN (ToNumber(undefined) not applied in + )

[proggeramlug]

Summary

number + typedArray[<out-of-bounds index>] evaluates to undefined instead of the spec-mandated NaN. The out-of-bounds typed-array element read correctly yields undefined, but the subsequent numeric + fails to ToNumber it (which should give NaN), and the TAG_UNDEFINED sentinel leaks through to the result.

Repro

function readAdd(S: Int32Array, i: number): number {
  return 1000 + S[i];
}
const a = Int32Array.from([10, 20, 30, 40]);
console.log(readAdd(a, 99));  // Node: NaN   Perry: undefined
console.log(readAdd(a, -1));  // Node: NaN   Perry: undefined
console.log(1000 + a[99]);    // Node: NaN   Perry: undefined

node --experimental-strip-types prints NaN for all three; Perry prints undefined.

Scope / notes

• Pre-existing and independent of any fast path: reproduces regardless of PERRY_TA_PARAM_F64_READ (on and off are bit-exact), i.e. it's present for the plain js_typed_array_get read path on main.
• Likely in the + lowering / js_dynamic_string_or_number_add handling of an undefined (TAG_UNDEFINED) operand: it should apply ToNumber(undefined) = NaN, not propagate the undefined sentinel. Other numeric ops (-, *) may share the bug (1000 - a[99], 2 * a[99]).
• String(a[99]) → "undefined", a[99] === undefined → true, and a[99] | 0 → 0 are all correct; only the ToNumber-via-arithmetic path is wrong.
• Found while validating perf(codegen): inline checked-f64 typed-array-param reads in numeric context #6883 (whose gap test deliberately observes OOB reads in === undefined / String() contexts to avoid this unrelated bug). Does not affect bcrypt (_encipher indices are all masked in-bounds).