Three follow-ups on the longest-prefix pricing match landed in this PR:
- Prefix match now requires a dash boundary or end-of-string. The
longest-key sort alone still falsely landed "claude-opus-4-15" on
the "claude-opus-4-1" row, and "gpt-5.5-prod" on the "gpt-5.5-pro"
row (a 6x overcharge). Demanding the next character be "-" rules
out the lookalikes while keeping dated snapshots
("gpt-5.4-mini-2026-04-23", "claude-opus-4-7-20260414") landing on
their canonical row.
- Clamp every token count to >= 0. A corrupted upstream payload
(negative cached count, off-by-one in a fixture) could previously
produce a negative bill that masked real spend in the session
total tooltip.
- Tolerate a non-dict "cache_creation" (e.g. an upstream proxy
folded the field down to a single int). The current code raised
AttributeError mid-turn; now it falls back to the 5m-default
bucket so the rest of the cost calculation still runs.
Adds tests/test_pricing_edge.py with 20 adversarial cases covering
the boundary check, negative / None / zero token values across both
envelopes, cache_read > prompt corruption, the OpenAI long-context
threshold crossover on cache-inflated billable input, malformed
sub-objects, and unknown-provider degradation. Combined suite is
51 tests, all green.
b4bce2d69b