- Fall back to top-level token usage when Codex response usage contains only service tier metadata
- Propagate parsed service tier while retaining top-level token counts
- Avoid early return during stream usage observation for chunks with zero token counts
Closes: #6261
- Add `ParsePluginExecutorResponseUsage` to extract token usage from non-streaming plugin responses across Claude, Gemini, Interactions, Antigravity, and OpenAI/Codex protocols.
- Add `ObservePluginExecutorStreamUsage` to observe and aggregate token usage across streaming chunks.
Closes: #5340