nilpy: builtin runtime errors are not catchable

• Type: feature (Nil-Python frontend, exception model) — Track N
• Status: done
• Opened: 2026-07-26 — probing songformatter under nilpy ([[feature-demo-songformatter-pxx-target]]).

Repro

try:
    x = int("nope")
except ValueError:
    print("caught ValueError")     # never reached
# -> Runtime error: int() got a string that is not a number: nope  (process aborts)

try:
    x = 1 // 0
except:
    print("caught")                # never reached
# -> Runtime error 200 (division by zero)  (process aborts)

raise ValueError("mine") from Python code IS caught, so the machinery works — what's missing is that errors raised by the runtime itself don't enter it.

Why it matters

Guarding a conversion with try/except is how real Python validates input. songformatter relies on it: settings parsing (int(get(...))) and the image= size/position parsing are wrapped in try/except and are expected to fall back to defaults, not abort the render.

Shape

Raise the builtin exception types from the runtime helpers (ValueError from int()/float() conversions, ZeroDivisionError, IndexError, KeyError) so the existing handler path catches them, including a bare except:.

Gate

make test-nilpy green with a .npy case per error type diffed against CPython,

• --tier quick + self-host byte-identical.

Log

• 2026-07-31 — resolved, commit 8f658852bdd1c721d5b530c6d48d9a8e245033bd.