feat(host): enable GPU zero-copy by default on all backends

Now that the per-capture worker subprocess makes an NVENC EGL/CUDA driver
fault survivable (design/zerocopy-worker-isolation.md), the reason the NVENC
zero-copy path stayed opt-in is gone. zerocopy::enabled() now defaults ON for
both GPU backends (was ON VAAPI / OFF NVENC). Fallbacks are intact: VAAPI's
one-shot CPU auto-downgrade (VAAPI-gated, never trips for NVENC) and NVENC's
per-capture fallback + worker-death latch.

Reframe the shipped host.env examples and setup guides to rely on the default
rather than force PUNKTFUNK_ZEROCOPY=1 (an explicit =1 skips the VAAPI
auto-downgrade).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs-site/content/docs/bazzite.md

@@ -85,13 +85,13 @@ cp /usr/share/punktfunk/host.env.bazzite ~/.config/punktfunk/host.env
 
 The template is deliberately minimal — it does **not** force a compositor, because the host
 auto-detects Gaming Mode (gamescope) vs Desktop (KWin) on every connect and follows the switch
-mid-stream. The only settings that matter are the session anchors plus zero-copy:
+mid-stream. The only settings that matter are the session anchors (GPU zero-copy is on by default):
 
 ```sh
 XDG_RUNTIME_DIR=/run/user/1000
 DBUS_SESSION_BUS_ADDRESS=unix:path=/run/user/1000/bus
 PUNKTFUNK_VIDEO_SOURCE=virtual
-PUNKTFUNK_ZEROCOPY=1            # GPU zero-copy (dmabuf → CUDA → NVENC); auto-falls back to CPU
+# GPU zero-copy (dmabuf → CUDA → NVENC) is ON by default; auto-falls back to CPU. Set =0 to force CPU.
 PUNKTFUNK_GAMESCOPE_ATTACH=1    # Gaming Mode = attach to the box's own session (see below)
 ```
 

docs-site/content/docs/configuration.md

@@ -36,7 +36,7 @@ On Linux the host **rewrites `WAYLAND_DISPLAY` / `XDG_CURRENT_DESKTOP` / `XDG_RU
 |---|---|---|
 | `PUNKTFUNK_COMPOSITOR` | `kwin` · `mutter` · `gamescope` · `wlroots` (aliases: `kde`/`plasma`, `gnome`, `sway`/`hyprland`) | Which backend creates the virtual display. **Leave unset to auto-detect;** set only to force one. |
 | `PUNKTFUNK_VIDEO_SOURCE` | `virtual` · `portal` | `virtual` creates a per-client display at the client's exact mode (the normal choice). `portal` captures an existing monitor instead. |
-| `PUNKTFUNK_ZEROCOPY` | `1` · `0` | GPU zero-copy capture→encode (dmabuf → CUDA → NVENC, or D3D11 on Windows). Leave on; it falls back to a CPU path automatically. |
+| `PUNKTFUNK_ZEROCOPY` | `1` · `0` *(default on)* | GPU zero-copy capture→encode (dmabuf → CUDA → NVENC, or D3D11 on Windows). **On by default** — no need to set it; it falls back to a CPU path automatically. Set `0` to force the CPU path. |
 | `PUNKTFUNK_INPUT_BACKEND` | `libei` · `gamescope` · `wlr` · `uinput` | How input is injected. `libei` for GNOME/KDE, `gamescope` for Bazzite/gamescope, `wlr` for Sway/wlroots. Auto-detected with the compositor. |
 | `PUNKTFUNK_ENCODER` | `auto` · `nvenc` · `vaapi` (Linux) · `amf` · `qsv` (Windows) · `software` | Encoder backend. `auto` (default) detects the GPU vendor: NVIDIA→NVENC, AMD→VAAPI/AMF, Intel→VAAPI/QSV. `software` (aliases `sw`/`openh264`) is the GPU-less H.264 path on both platforms — on Windows `auto` falls back to it when no GPU is found; on Linux it is **explicit-only** (`auto` never picks it). |
 | `PUNKTFUNK_RENDER_NODE` | path | Linux DRM render node for zero-copy (default `/dev/dri/renderD128`). Set on multi-GPU boxes to pick the right GPU. |

docs-site/content/docs/gnome.md

@@ -21,7 +21,7 @@ WAYLAND_DISPLAY=wayland-0
 XDG_CURRENT_DESKTOP=GNOME
 PUNKTFUNK_COMPOSITOR=mutter
 PUNKTFUNK_VIDEO_SOURCE=virtual
-PUNKTFUNK_ZEROCOPY=1
+# GPU zero-copy (dmabuf → CUDA → NVENC) is ON by default; auto-falls back to CPU. Set =0 to force CPU.
 PUNKTFUNK_INPUT_BACKEND=libei
 ```
 

docs-site/content/docs/kde.md

@@ -20,7 +20,7 @@ WAYLAND_DISPLAY=wayland-0
 XDG_CURRENT_DESKTOP=KDE
 PUNKTFUNK_COMPOSITOR=kwin
 PUNKTFUNK_VIDEO_SOURCE=virtual
-PUNKTFUNK_ZEROCOPY=1
+# GPU zero-copy (dmabuf → CUDA → NVENC) is ON by default; auto-falls back to CPU. Set =0 to force CPU.
 PUNKTFUNK_INPUT_BACKEND=libei
 ```
 

docs-site/content/docs/sway.md

@@ -27,7 +27,7 @@ these in `~/.config/punktfunk/host.env`:
 PUNKTFUNK_COMPOSITOR=wlroots      # aliases: sway, hyprland
 PUNKTFUNK_INPUT_BACKEND=wlr
 PUNKTFUNK_VIDEO_SOURCE=virtual
-PUNKTFUNK_ZEROCOPY=1              # GPU zero-copy capture→encode; auto-falls back to CPU
+# GPU zero-copy capture→encode is ON by default; auto-falls back to CPU. Set PUNKTFUNK_ZEROCOPY=0 to force CPU.
 ```
 
 See [Configuration](/docs/configuration) for the full reference.