bug: a refusal reply with null content throws in the parser and loses its token usage #82

Problem

OpenAICompatibleProvider.parseProviderResponse reads message("content").str unconditionally. OpenAI's structured-output refusals return content: null with a refusal string and a full usage block. The parser throws before parseUsage runs, so the extension reports a parse failure and records neither the call nor its tokens, even though the provider billed them. Same shape can appear on any OpenAI-compatible provider.

Found by a Codex review on 2026-09-08. The parser assumption predates today's changes; the accounting consequence is new with #78.

Fix

Treat missing or null content as an empty string, carry the refusal text on the response (or surface it as the content with a clear marker), parse usage regardless, and let the calling primitive decide what to do with a refusal after recordUsage.

Test

A canned refusal body in UsageParsingSpec asserting usage is parsed, plus a tests.txt case asserting the call is counted.