Sterling reported 'json_error: no field input/input_tokens' still firing
despite existing serde(default) in types.rs. Root cause: SSE streaming
path had a separate deserialization site that didn't use the same defaults.
- Add serde(default) to sse.rs UsageEvent deserialization
- Add serde(default) to types.rs Usage struct fields (input_tokens, output_tokens)
- Add regression test with empty-usage JSON response in streaming context
The Rust API layer rejected thinking-enabled responses because it only recognized text and tool_use content blocks. This commit extends the response and SSE parser types to accept reasoning-style content blocks and deltas, with regression coverage for both non-streaming and streaming responses.
Constraint: Keep parsing compatible with existing text and tool-use message flows
Rejected: Deserialize unknown content blocks into an untyped catch-all | would weaken protocol coverage and test precision
Confidence: high
Scope-risk: narrow
Directive: Keep new protocol variants covered at the API boundary so downstream code can make explicit choices about preservation vs. ignoring
Tested: cargo test -p api thinking -- --nocapture
Not-tested: Live API traffic from a real thinking-enabled model
