Features

• Add data stream progress to core-modules: readers get next_progress(), which counts received bytes, and send_text, send_bytes and send_file take an optional progress delegate (StreamProgressDelegate) inside their options record, defaulting to none and ignored by incremental streams. The core adds on_progress on SendTextOptions and SendByteOptions and a progress_stream() accessor on the concrete readers that does not borrow the reader. The generated Swift option records no longer conform to Equatable or Hashable.
• Let an incremental text stream declare its total length in the header: the core adds StreamTextOptions::total_length, and the core-modules StreamTextOptions record gets an optional total_length that stream_text passes to it. The receiver then reports progress against it and fails the stream if the length does not match.
• Add close() to the core-modules text and byte stream readers (closeStream() in Kotlin) and core StreamCloser handles returned by closer() to end pending reads with DataStreamError::AlreadyClosed and remove streams exactly once; dropping a reader has the same effect.
• The core-modules text and byte stream writers' close takes an optional reason, which closes the stream abnormally, and attributes to send in the stream's trailer, which default to none and an empty map. This and the other changed or new data stream methods change the generated Swift protocols and Kotlin interfaces, so a hand-written conformer such as a test mock must be updated.
• Replace CaptureSourceEvent with JoinCaptureRequest, which waits for a running capture to end and returns its result, and make disposing a capture handle wait until its capture thread exits.
• Create the well-known data channels as negotiated (fixed IDs) when the server supports it (protocol 18), saving the data channel open handshake round trip. Falls back to in-band channels against older servers.
• Signal sessions can now be driven over UniFFI: foreign callers can connect, send and receive encoded signal messages, resume, and close a livekit-signaling session with a host-supplied WebSocket transport.

Fixes

• Keep NVIDIA's Jetson video codec plugin loaded while probing MMAPI encoder capabilities, preventing probe teardown from breaking subsequent GStreamer capture.
• Report encoded capture sources as VIDEO_SOURCE_ENCODED, so their video source accepts encoded frame and feedback requests and rejects raw frames.
• An incoming single-packet (inline) data stream whose payload is shorter or longer than the length in its header now fails with StreamError::Incomplete or StreamError::LengthExceeded, as a chunked stream already does. Before, it ended successfully.
• Split outgoing data stream options into SendTextOptions, shared SendByteOptions, StreamTextOptions and StreamByteOptions, all #[non_exhaustive]. Remove send_file_with_progress and stream_text_with_total_length in favor of on_progress and total_length on the options.
• A data stream that its sender closes early with a reason now fails with that reason (StreamError::AbnormalEnd), as in JS, even when its header declared a total length; before, the reader got StreamError::Incomplete.
• Release local tracks when the server ends the room by detaching publisher senders before the publisher PeerConnection closes, and make RtpSender::track() return None for a detached sender instead of dereferencing null.
• The info() of a core-modules data stream reader now includes the attributes from the stream's trailer, which the reader used to drop. They are present once the read that ends the stream returns.
• Expose inference and observability grants on the UniFFI access-token surface: TokenOptions gains inference_grants and observability_grants, and verified Claims carry inference and observability.
• Add InferenceGrants and AccessToken::with_inference_grants, so Rust services can mint tokens for LiveKit Inference.
• livekit-signaling: add an opt-out for region failover in connect - #1567 (@lukasIO)
• livekit-signaling: let callers set the advertised protocol and capabilities - #1569 (@lukasIO)
• Add ObservabilityGrants and AccessToken::with_observability_grants, so Rust services can mint tokens that publish observability data.
• Remove the use_legacy_data_streams migration flag. The FFI RoomDataStreamOptions.use_legacy_client_implementation field is now deprecated and ignored, and the hidden RoomDataStreamOptions::with_legacy_client_implementation builder and the hidden SignalOptions::use_legacy_data_streams field are gone; clients always advertise data streams v2 support.