(1) Malformed numbers — the open question, stated as a goal

Do we want readln(n) on input that is not a number to stop the program, or to hand back a value and continue?

FPC stops (RTE 106). We continue. Neither is a mechanism problem — both are one line in the same parser — so this is worth deciding once rather than per row.

What is measured (2026-09-18, identical on all five backends):

The argument for FPC's answer is that ours is the silent-wrong-value shape this repo keeps paying for: a program reading numbers from a file gets plausible garbage and no signal. The argument for ours is that halting is a poor default for a library-grade runtime and the caller has no way to opt out. Nobody has made the case from real source yet, which is what would settle it — find a program that depends on either behaviour.

Note the 300 -> 44 row is the same wrap a cast gives, so it is at least self-consistent with the rest of the language.

(2) A Char read from an empty line — measured, and ours is chosen

input:  "\nALPHA\nBETA\n"
readln(c);  readln(s1);  readln(s2);

pxx   c=10  s1=[ALPHA]  s2=[BETA]
FPC   c=10  s1=[BETA]   s2=[]

Both agree the Char is #10 (that half was a genuine bug and was FIXED the same day — test_read_char_preserves_the_line_terminator.pas). They differ on what the enclosing readln does afterwards: ours has nothing left to skip, because the terminator WAS the character; FPC skips to past the next one and eats ALPHA.

Reading a Char from a line that has none is a program that has already made a mistake. Given that, the behaviour that keeps the next line is the one that leaves the mistake visible, so this is chosen, not tolerated, and a ticket reopening it needs real source that wants FPC's skip.

What is NOT divergent, so nobody re-measures it

Fifteen shapes, five backends, byte-identical to each other and (where FPC does not halt) to FPC: blanks before a sign, a tab before a sign, leading zeros, an in-range value into a Byte, two Chars from one line, two integers on one line, a second integer past end of line, a string taking the rest of a line including its inner and trailing blanks, a string[N] capacity clamp, the read/readln/Eof interleave, the character scan loop, and a line longer than any buffer.