fix(host): actionable NVENC error logging — drop misleading "(no NVIDIA GPU?)"

Every NVENC entry-point failure was annotated "(no NVIDIA GPU?)", which
misled triage: the direct-NVENC path only loads on a machine that HAS an
NVIDIA GPU. A Linux user hit NV_ENC_ERR_INVALID_VERSION at
open_encode_session_ex (past the NvEncodeAPIGetMaxSupportedVersion pre-flight
gate) — the signature of a userspace/kernel driver version skew that a host
reboot fixes — and the log pointed at a missing GPU instead. A restart did
fix it.

Add encode/nvenc_status.rs: a shared NVENCSTATUS -> cause mapper that folds
the real cause into the anyhow::Error at construction, so every downstream
{e:#} log (the encode-recovery loop, session teardown) improves for free.
INVALID_VERSION now reads "update the NVIDIA driver, or reboot if you just
updated it (a host restart is the usual fix)"; NO_ENCODE_DEVICE /
DEVICE_NOT_EXIST / INCOMPATIBLE_CLIENT_KEY (session-count limit) / OOM /
UNSUPPORTED_PARAM get their own glosses. The required API version comes from
the SDK consts so it stays correct across crate bumps.

Wire it into all NVENC entry-point failures in both backends
(encode/linux/nvenc_cuda.rs, encode/windows/nvenc.rs) — every open, init,
preset/resource/bitstream call.

Also: when the encode-recovery loop exhausts its in-place rebuilds it now
logs a clear terminal line with the underlying cause instead of the session
silently vanishing after the last identical "rebuilt in place" line.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/punktfunk-host/src/encode/linux/nvenc_cuda.rs

@@ -31,6 +31,7 @@
 // Every `unsafe` block / impl in this file carries a `// SAFETY:` proof; enforce it.
 #![deny(clippy::undocumented_unsafe_blocks)]
 
+use super::nvenc_status;
 use super::{ChromaFormat, Codec, EncodedFrame, Encoder, EncoderCaps};
 use crate::capture::{CapturedFrame, FramePayload};
 use crate::zerocopy::cuda::{self, InputSurface};
@@ -448,9 +449,7 @@ impl NvencCudaEncoder {
         let mut enc: *mut c_void = ptr::null_mut();
         (api().open_encode_session_ex)(&mut params, &mut enc)
             .nv_ok()
-            .map_err(|e| {
-                anyhow!("NVENC open_encode_session_ex (caps probe): {e:?} (no NVIDIA GPU?)")
-            })?;
+            .map_err(|e| nvenc_status::call_err("open_encode_session_ex (caps probe)", e))?;
         let wmax = self.get_cap(enc, nv::NV_ENC_CAPS::NV_ENC_CAPS_WIDTH_MAX);
         let hmax = self.get_cap(enc, nv::NV_ENC_CAPS::NV_ENC_CAPS_HEIGHT_MAX);
         let yuv444 = self.get_cap(enc, nv::NV_ENC_CAPS::NV_ENC_CAPS_SUPPORT_YUV444_ENCODE);
@@ -512,7 +511,7 @@ impl NvencCudaEncoder {
             &mut preset,
         )
         .nv_ok()
-        .map_err(|e| anyhow!("get_encode_preset_config_ex: {e:?}"))?;
+        .map_err(|e| nvenc_status::call_err("get_encode_preset_config_ex", e))?;
         let mut cfg = preset.presetCfg;
 
         // CBR, infinite GOP, P-only, ~1-frame VBV (mirror the Windows/Linux-libav RC config).
@@ -683,7 +682,7 @@ impl NvencCudaEncoder {
         let mut enc: *mut c_void = ptr::null_mut();
         (api().open_encode_session_ex)(&mut params, &mut enc)
             .nv_ok()
-            .map_err(|e| anyhow!("NVENC open_encode_session_ex: {e:?} (no NVIDIA GPU?)"))?;
+            .map_err(|e| nvenc_status::call_err("open_encode_session_ex", e))?;
 
         let mut cfg = match self.build_config(enc, bitrate) {
             Ok(cfg) => cfg,
@@ -698,7 +697,7 @@ impl NvencCudaEncoder {
             Ok(()) => Ok(enc),
             Err(e) => {
                 let _ = (api().destroy_encoder)(enc);
-                Err(anyhow!("initialize_encoder: {e:?}"))
+                Err(nvenc_status::call_err("initialize_encoder", e))
             }
         }
     }
@@ -818,7 +817,7 @@ impl NvencCudaEncoder {
                 };
                 (api().create_bitstream_buffer)(enc, &mut cb)
                     .nv_ok()
-                    .map_err(|e| anyhow!("create_bitstream_buffer: {e:?}"))?;
+                    .map_err(|e| nvenc_status::call_err("create_bitstream_buffer", e))?;
                 self.bitstreams.push(cb.bitstreamBuffer);
             }
 
@@ -849,7 +848,7 @@ impl NvencCudaEncoder {
                 };
                 (api().register_resource)(self.encoder, &mut rr)
                     .nv_ok()
-                    .map_err(|e| anyhow!("register_resource (CUDADEVICEPTR): {e:?}"))?;
+                    .map_err(|e| nvenc_status::call_err("register_resource (CUDADEVICEPTR)", e))?;
                 self.ring.push(RingSlot {
                     surface,
                     reg: rr.registeredResource,
@@ -1014,7 +1013,7 @@ impl Encoder for NvencCudaEncoder {
             };
             (api().map_input_resource)(self.encoder, &mut mp)
                 .nv_ok()
-                .map_err(|e| anyhow!("map_input_resource: {e:?}"))?;
+                .map_err(|e| nvenc_status::call_err("map_input_resource", e))?;
 
             let pts = self.frame_idx as u64;
             self.frame_idx += 1;
@@ -1086,7 +1085,7 @@ impl Encoder for NvencCudaEncoder {
             }
             (api().encode_picture)(self.encoder, &mut pic)
                 .nv_ok()
-                .map_err(|e| anyhow!("encode_picture: {e:?}"))?;
+                .map_err(|e| nvenc_status::call_err("encode_picture", e))?;
             self.pending.push_back((
                 self.bitstreams[slot],
                 mp.mappedResource,
@@ -1186,7 +1185,7 @@ impl Encoder for NvencCudaEncoder {
             };
             (api().lock_bitstream)(self.encoder, &mut lock)
                 .nv_ok()
-                .map_err(|e| anyhow!("lock_bitstream: {e:?}"))?;
+                .map_err(|e| nvenc_status::call_err("lock_bitstream", e))?;
             let data = std::slice::from_raw_parts(
                 lock.bitstreamBufferPtr as *const u8,
                 lock.bitstreamSizeInBytes as usize,
@@ -1198,7 +1197,7 @@ impl Encoder for NvencCudaEncoder {
             );
             (api().unlock_bitstream)(self.encoder, bs)
                 .nv_ok()
-                .map_err(|e| anyhow!("unlock_bitstream: {e:?}"))?;
+                .map_err(|e| nvenc_status::call_err("unlock_bitstream", e))?;
             if !map.is_null() {
                 let _ = (api().unmap_input_resource)(self.encoder, map);
             }