fix: reject non-finite prices and escape a model named DEFAULT

float() accepts "nan" and "inf", so a hand-edited models.ini could feed
either into the cost arithmetic and render "$nan". Rejected once in _get
rather than at each downstream call site.

A model whose id is literally DEFAULT wrote a [DEFAULT] section, which a
stock configparser reader treats as defaults inherited by every other
model. Since the file is documented for hand-editing, that reintroduces
the contamination the renamed default_section exists to prevent, so the
id is escaped on write and mapped back on read.

Also drops the marker branch in save(), leaving mark_skipped() as the
sole writer of the "marker present iff no real keys" invariant, and
prunes two test blocks that could not fail.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

0 files changed, 0 insertions, 0 deletions