If upstream omits reasoning-end and starts emitting text-delta or
tool-call events, the thinking block remained open causing
thinking_start -> thinking_delta -> text_start -> ... -> thinking_end
ordering. Now endThinking() is called at the start of text-delta and
tool-call handlers so thinking_end always precedes text_start or
toolcall_start.
Adds 2 regression tests for the missing reasoning-end edge case.
Document the incremental reasoning-delta streaming, live display pricing,
and dynamic model fetch in CHANGELOG.md. Add a Pricing section to
README.md explaining the MODEL_COSTS overlay and how to update prices.
Add tests/test-pricing.ts to assert that known models have non-zero
pricing, promotional deals are documented in comments, and Claude models
include cache pricing. Fix test-pi-local to match against combined
stdout+stderr since pi may output model listing to either stream.
Patrick Wozniak