C ABI: 16 → 25 symbols
- SSE C ABI (6 symbols)
- Per-request headers + timeout
- Cancel all, CB state, metrics, adaptive timeout
- TLS/DNS/Proxy/Redirect config passthrough
- WS headers/protocols/deflate/race_count
- Network quality history

142 Rust + 323 TS + 38 E2E = 503 tests passing