`int[] + int + int[]` compiles but is lowered as byte concatenation and fails at runtime

[michaelsutton]

int[] + int + int[] currently compiles, but the generated script does not preserve int[] element boundaries. At runtime, the middle int is coerced to a single byte and concatenated into the serialized int[] blob, so later int[] indexing reads the wrong 8-byte chunks.

Minimal repro

contract Arrays() {
    entrypoint function main() {
        int[] left = [1, 2];
        int middle = 3;
        int[] right = [4, 5];
        int[5] mixed = left + middle + right;

        require(mixed[0] == 1);
        require(mixed[1] == 2);
        require(mixed[2] == 3); // fails here
        require(mixed[3] == 4);
        require(mixed[4] == 5);
    }
}

Observed behavior
The contract compiles, but execution fails on require(mixed[2] == 3).

Expected behavior
One of these should happen:

1. int[] + int + int[] is supported and lowers by serializing the scalar int as an 8-byte int element before concatenation.
2. The compiler rejects this expression as unsupported/type-invalid.

Root cause
BinaryOp::Add currently switches to concat mode whenever either side is considered “bytes-like”. int[] is treated as bytes-like because is_bytes_type() falls back to is_array_type(type_name). In concat mode, non-bytes operands are coerced with OP_NUM2BIN(1), so the scalar int is inserted as a 1-byte payload instead of an 8-byte int element.

This means:

• left + middle becomes byte concat
• middle is encoded as 1 byte
• later int[] indexing still assumes 8-byte element boundaries

Notes

• int[] + int[] works.
• The issue is specifically with mixing int[] concatenation and scalar int.
• byte[] + byte currently works, but for type-system consistency it may also be better to disallow mixing array and scalar operands unless the scalar is explicitly cast to the array element encoding (byte[1], byte[8], etc.). That would make concat semantics uniform across byte[] and int[] instead of relying on implicit scalar coercions for some element types but not others.