fix(desktop): recover frame references and bound relay qualification

[rldyourmnd]

A newer delta interrupted its predecessor even though it could depend on that frame; queue drops also left the sender emitting broken reference chains. Preserve partial delta writes before dependent successors, allow an independent keyframe to replace an in-flight delta, and request IDR after any encoded admission loss. Bound queue collapse and refuse noncontiguous deltas until an IDR after final pacing selection. Keep the existing two-slot queue and wire contract.

Validation: a partial-delta regression failed before the fix; fmt and default/X11 workspace clippy pass; 555 workspace tests and 28 X11 unit tests pass. Native H.264 coverage checks a pixel after a lost reference and IDR recovery. Seven serial real-QUIC session scenarios pass on clean source, including a 60-second synthetic-header measurement (p95 3 ms clean; impaired queue p95 37 ms, age p95 110 ms). These are not displayed-pixel or real-codec network latency claims. An intermediate FIFO-only prototype failed the unchanged queue-age limit and was replaced; no threshold was relaxed.

Exact source, hashes, results and limits: docs/reports/rds-desktop-references-20260926.md and its JSON companion. The first GitHub Linux run stalled in the pre-existing unbounded relay_forwards_handshake_and_datagrams fixture. The live log identified the scenario but not its blocked await. Add five-second per-phase deadlines/diagnostics, scoped connect/accept ownership and explicit cleanup; retain every original identity/payload/forwarding assertion. One full local run plus a fixed ten-run batch passed all six owned-relay scenarios (66 executions), and scoped clippy passes. This improves bounded failure diagnosis; it does not claim a localized relay-runtime fix. GitHub qualification for final head 314ab2d1a6bc92cda255fe6eb87b62534aae2257 is complete: Linux/macOS CI, CodeQL, supply chain and native packaging all passed. The Linux log confirms the bounded owned-relay scenario, native H.264 reference recovery, and all seven dedicated Xvfb capture/input checks executed and passed. This is a W6.1 increment; real-codec impairment/overload qualification, viewer/rendering, wire session IDs and platform/input-to-visible gates remain open. No deployment or release is introduced.