The last §2.3 seam-trait tightening: give `Encoder` a `caps() -> EncoderCaps`
so the session glue routes by *query* instead of relying on the no-op/`false`
defaults of `invalidate_ref_frames`/`set_hdr_meta`.
`EncoderCaps { supports_rfi, supports_hdr_metadata }` is a cheap `Copy` struct.
The trait gains a default `caps()` returning `EncoderCaps::default()` (all
false) — correct for every SDR/libavcodec backend (Linux NVENC, VAAPI, AMF/QSV,
software openh264), so they need no change. Only the Windows direct-NVENC path
(`NvencD3d11Encoder`) overrides it, reporting the real `rfi_supported` (probed
once at open via `nvEncGetEncodeCaps`) and `hdr` (HDR-SEI on keyframes).
Consumer: the GameStream encode loop (`gamestream/stream.rs`) hoists
`supports_rfi` once before the loop and gates the loss-recovery path on it —
`!(supports_rfi && enc.invalidate_ref_frames(..))` forces a keyframe directly
on non-RFI encoders instead of making an always-`false` call every loss event.
Behaviour-preserving (same keyframe/RFI outcome), one fewer no-op call, intent
explicit. The native host (punktfunk1) uses FEC+keyframes, no RFI consumer.
Linux `cargo clippy -p punktfunk-host --all-targets -D warnings` clean; the
three edited files are rustfmt-clean. The NVENC override is Windows-only
(1:1 with the existing impl style) → CI/on-glass gate.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
enricobuehler
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