reward: normalize_math_answer leaves a trailing backslash on LaTeX-escaped set braces \{...\}

[philluiz2323]

Bug

normalize_math_answer in src/trinity/orchestration/reward.py strips a single outer pair of { } / \{ \} with a greedy capture group:

# Strip a single outer pair of \{ \} or { }.
s = re.sub(r"^\\?\{(.*)\\?\}$", r"\1", s).strip()

For LaTeX-escaped set braces \{ … \}, the greedy (.*) swallows the closing backslash and the optional \\? matches nothing, leaving a stray trailing backslash in the normalized answer.

Reproduce (offline, no network/GPU)

from trinity.orchestration.reward import normalize_math_answer, math_equal
normalize_math_answer(r'\{5\}')       # -> '5\\'    (should be '5')
normalize_math_answer(r'\{1,2,3\}')   # -> '1,2,3\\'(should be '1,2,3')
math_equal(r'\{1,2,3\}', '1,2,3')     # -> False    (should be True)
normalize_math_answer('{5}')          # -> '5'      (unescaped case is fine)

Impact

Any math item whose gold answer or model output formats a set with escaped braces (\{a,b,c\}, common in MATH-style solutions) is graded as a false negative — the two sides are equal but compare unequal because one carries a trailing backslash. This silently understates accuracy on set-valued answers.

Expected

The escaped-brace pair should be stripped cleanly: \{1,2,3\} → 1,2,3.

Fix

Make the inner capture non-greedy so the optional trailing \\? can claim the escaping backslash:

s = re.sub(r"^\\?\{(.*?)\\?\}$", r"\1", s).strip()

Location

src/trinity/orchestration/reward.py, normalize_math_answer (the "Strip a single outer pair" line, ~819).