fix(session): ignore malformed model costs

Merged
NE
3mo ago
+23-9

Summary

  • treat malformed or non-finite model cost fields as zero during usage accounting
  • preserve valid pricing components and existing finite-price behavior
  • add a regression test for provider-supplied object values

Closes #43098

Testing

  • bun test test/session/compaction.test.ts --test-name-pattern "SessionNs.getUsage"
  • bun typecheck in packages/opencode
  • full workspace typecheck from the pre-push hook