Python validates the body with pydantic as before. Rust parses the same
bytes with serde into `SlidingSyncBody`, which follows the pydantic model
field for field, including where it tells an explicit `null` from a missing
field. Lists and room subscriptions keep document order, and a repeated key
keeps its first position and last value, as the dict `json.loads` builds.
`SlidingSyncRequest` is the body plus what Python adds: the user and device,
the room key and connection position of `pos`, the room key and string suffix
of the token the response runs up to, the admin's soft-failed policy, whether
the background updates have finished, the excluded rooms and the extension
flags. `SlidingSyncHandler._build_rust_request` builds it.
The servlet keeps the body's bytes in `SlidingSyncConfig.body_bytes` when the
Rust handler is in use. A config built without a request is re-encoded.
`tests/rest/client/sliding_sync/test_rust_request.py` parses 400 generated
bodies (unknown fields, nulls, repeated keys, escapes) both ways and
compares, and checks the re-encoding parses the same.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01R5b7Ruy4cgt27Mjq6Ptxbb
