bug: `sort -n` doesn't extract leading numeric prefix from strings

[chaliy]

Problem

sort -n correctly sorts pure numeric input but fails to extract leading numeric prefixes from strings. In real coreutils sort -n, lines like 0003-msg.md are sorted by their leading number 3, with non-numeric suffixes compared lexically as tiebreakers.

Additionally, sort -t DELIM -k FIELD (field-based sorting) does not sort correctly.

Both patterns are used by wedow/harness for:

• Ordering message sequence files: ls -1 msgs/ | sort -n | tail -1
• Ordering hook scripts: printf '%s\n' "${order[@]}" | sort -t/ -k1,1

Reproduction

# Pure numbers — works:
printf '3\n1\n2\n' | sort -n
# Output: 1 2 3 ✓

# Strings with numeric prefix — broken:
printf '0003-msg.md\n0001-msg.md\n0002-msg.md\n' | sort -n
# Expected: 0001-msg.md  0002-msg.md  0003-msg.md
# Actual:   0003-msg.md  0001-msg.md  0002-msg.md  (unsorted)

# Field-based sort — broken:
printf 'assemble/20-tools\nassemble/10-init\nassemble/30-end\n' | sort -t/ -k1,1
# Expected: assemble/10-init  assemble/20-tools  assemble/30-end
# Actual:   assemble/20-tools  assemble/10-init  assemble/30-end  (unsorted)

Test cases

sort -n with numeric prefix strings

printf '0003-msg.md\n0001-msg.md\n0002-msg.md\n' | sort -n
# Expected stdout:
#   0001-msg.md
#   0002-msg.md
#   0003-msg.md

sort -n with mixed prefix lengths

printf '10-exec\n20-tools\n5-first\n' | sort -n
# Expected stdout:
#   5-first
#   10-exec
#   20-tools

sort -n treats non-numeric lines as 0

printf 'zzz\n2-second\naaa\n1-first\n' | sort -n
# Expected stdout:
#   aaa
#   zzz
#   1-first
#   2-second
# (non-numeric lines have value 0 and are compared lexically among themselves)

sort -t with -k (field-based)

printf 'assemble/20-tools\nassemble/10-init\nassemble/30-end\n' | sort -t/ -k2,2
# Expected stdout:
#   assemble/10-init
#   assemble/20-tools
#   assemble/30-end

sort -t/ -k1,1 (harness hook ordering)

printf 'z/20-tools\na/10-init\nm/30-end\n' | sort -t/ -k1,1
# Expected stdout:
#   a/10-init
#   m/30-end
#   z/20-tools

sort -n -r (reverse numeric)

printf '1\n3\n2\n' | sort -n -r
# Expected stdout:
#   3
#   2
#   1

sort -n with zero-padded numbers

printf '003\n010\n001\n' | sort -n
# Expected stdout:
#   001
#   003
#   010