Support opt-in psrpc bus compression

[paulwe]

psrpc v0.7.6 (psrpc#130) added opt-in gzip at the bus boundary, and protocol#1771 surfaced it as rpc.PSRPCConfig.Compression with a BusOptions() conversion. runService built the bus from the redis client alone, so there was no way to reach the setting.

psrpc:
  compression:
    quality: 6
    threshold: 1024
    max_decompressed_size: 0

Shape

Egress carried no rpc.PSRPCConfig at all, so this adds the whole block under a psrpc: key, matching livekit-server (livekit#4844) and ingress (ingress#488). Only compression is read here — egress uses the rpc.NewXClient(bus, opts...) shorthand and its own io_selection_timeout, so max_attempts, timeout, backoff and buffer_size are accepted for config parity but inert. The README says so.

It is seeded in the NewServiceConfig struct literal rather than InitDefaults, so the seed lands before the yaml unmarshal. Without that, a config setting only quality would leave Threshold at zero and compress every payload, however small. NewServiceConfig is the sole construction path — nothing else builds a ServiceConfig literal or calls InitDefaults — so the one seed covers the service and the integration runner.

PipelineConfig deliberately gets nothing. The per-session handler subprocess talks to the parent over unix-socket gRPC IPC and never builds a bus (see the comment at pkg/service/handler_proxy.go:27), so nothing else needed threading.

Compression is off by default

A peer on a psrpc older than v0.7.6 ignores the compression marker — psrpc deserializes with DiscardUnknown — and then decodes the gzipped bytes as the payload, so the message is dropped without an error. livekit-server, egress, ingress, SIP and agent workers share this bus, so enabling it is a two-stage operator action: roll v0.7.6+ everywhere, then raise quality at the publishers. The README says so at the setting.

max_decompressed_size only affects reading, so it can be set ahead of quality.

Testing

pkg/config/config_test.go gains coverage of the defaults and of an override that leaves Threshold at its default.

Verified the config actually reaches the compressor with a throwaway pub/sub over a local bus: the default config round-trips a 16 KB payload, quality: 6 round-trips it, and adding max_decompressed_size: 64 drops that same payload — which is what proves it was gzipped rather than skipped by the threshold. quality: 0 with the same cap delivers it.

Not verified against a live livekit-server; that needs a peer already on psrpc v0.7.6+. The integration suite was not run — it needs redis, chrome and a live server, and nothing here changes behavior at the default quality: 0.

Two pre-existing failures in go test ./... are unrelated and fail identically on main: m3u8.TestLivePlaylistWriter (wall-clock timestamp) and uploader.TestUploader (needs real AWS credentials).

Note on the protocol pin

v1.51.1-0.20260905133529-a4f4b5c0c23f is protocol main at the #1771 merge, the same pseudo-version livekit#4844 and ingress#488 use. It is 14 commits ahead of the previous pin and additive for egress — the only livekit/ package deletions in the range are in sip.go, and egress uses neither those nor the data-track packet code that moved in #1757.

[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.

[github-actions]

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