feat(moq-gst): add group-order feature, ascending/max-latency-ms properties, and consumer diagnostics

[santi-ferreiro]

Summary

Builds on top of c7e8ab58 Add group-order support, which added transport-layer support for ascending group ordering (Track::ordered, group_ascending in the relay priority queue) but did not propagate it to the GStreamer plugin layer.

This PR completes the work by exposing ascending and max-latency-ms as first-class GStreamer properties on moqsrc, declaring the group-order Cargo feature, and decoupling the two axes so callers control them independently. Consumer latency is always Duration::from_millis(max_latency_ms) with no special-casing of ascending mode.

Additionally, the Consumer in moq-mux gains structured INFO log lines that let callers distinguish three distinct causes of frame loss: budget drops, stream errors, and ordering discards.

A pre-merge review caught two additional property API issues, fixed before merge:

• None of the five ParamSpecBuilder chains called .mutable_ready(). Settings snapshot is taken once at ReadyToPaused and never re-read, so property writes after that transition are silently accepted but have no effect on the running session.
• The ascending property was registered unconditionally but compiles to a no-op (let _ = ascending;) when built without --features group-order. A caller setting ascending=true would see the getter return true while the relay always got ordered=false. Fixed by emitting gst::warning! in the #[cfg(not(feature = "group-order"))] arm.

Changed files

• rs/moq-gst/Cargo.toml — declares [features] section with group-order = [] (was referenced in source but never declared; building with --features group-order previously failed)
• rs/moq-gst/src/source/imp.rs — adds max_latency_ms/ascending to Settings/ResolvedSettings, exposes both as GStreamer properties, adds .mutable_ready() to all five property builders, emits warning when ascending is set without the feature, extracts subscribe_track() helper to avoid duplicating the #[cfg] block for video and audio tracks
• rs/moq-mux/src/container/consumer.rs — adds frames_in_current_group counter and three structured INFO log lines for loss attribution (budget drop / stream error / ordering discard)

Test plan

• cargo build --release --features group-order compiles cleanly
• moqsrc exposes max-latency-ms and ascending as inspectable GStreamer properties with correct defaults
• Ascending mode confirmed working end-to-end: 0 frame losses at every loss level from 1% to 50%; descending with same budget shows 597 losses at 50% — relay is receiving and honoring the ordered flag
• Stream errors and ordering discards confirmed absent under all test conditions; only budget drops appear in loss attribution logs

🤖 Generated with Claude Code

[gemini-code-assist]

Code Review

This pull request introduces max-latency-ms and ascending settings to the moq-gst GStreamer source element, allowing users to configure group delivery order and latency. Feedback on these changes highlights a potential compilation error when the group-order feature is enabled due to a missing ordered field in the moq_net::Track dependency. Additionally, it is recommended to update the description of the max-latency-ms property, as it is no longer ignored when ascending is set to true.

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[gemini-code-assist]

The moq_net::Track struct defined in rs/moq-net/src/model/track.rs does not currently have an ordered field. Enabling the group-order feature will result in a compilation error because track_ref.ordered does not exist.\n\nPlease ensure that the workspace dependency moq-net is updated to include the ordered field (as mentioned in the PR description regarding commit c7e8ab58), or that the required changes are merged/included in this branch.