feat: resident guest init (#333)

Get this thing going..







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<h2><a
href="https://app.greptile.com/api/retrigger?id=63134761"><picture><source
media="(prefers-color-scheme: dark)"
srcset="https://greptile-static-assets.s3.amazonaws.com/badges/RetriggerDark.svg?v=1"><source
media="(prefers-color-scheme: light)"
srcset="https://greptile-static-assets.s3.amazonaws.com/badges/Retrigger.svg?v=1"><img
alt="Retrigger"
src="https://greptile-static-assets.s3.amazonaws.com/badges/Retrigger.svg?v=1"
align="right"></picture></a>Confidence Score: 5/5</h2>

The PR appears safe to merge; all previous findings are resolved and the
latest readiness change introduces no established actionable regression.

<h3>Summary</h3>

- Establishes required guest filesystems, runtime directories, device
permissions, and service processes.
- Reports initialization and service deaths over the lifecycle channel.
- Supports launch, restart, and shutdown commands for a resident guest.
- Separates service and workload identities and configures per-launch
runtime environments.
- Removes the currently inactive nescope screenshot option and makes
capture-chain verification fail explicitly when compositor readback is
unavailable.
- Reworks the guest image around `nesinit` as PID 1 without a
distribution service manager.

<h3>Diagram</h3>

```mermaid
sequenceDiagram
    participant Host
    participant Init as nesinit
    participant FS as Guest filesystems
    participant Services as Service stack
    participant Workload

    Init->>Host: Ready(protocol version)
    Host->>Init: Boot(mount descriptors)
    Init->>FS: Establish and mount shares
    Init->>Services: Spawn services in order
    Services-->>Init: Required sockets ready
    Init->>Host: Initialized(service names)
    Host->>Init: Launch(id, exec, on_exit)
    Init->>Workload: Spawn with isolated UID/runtime
    Init->>Host: Started(id)
    Workload-->>Init: Exit status
    Init->>Host: WorkloadExited(id, status)
    Host->>Init: Launch / Restart / Shutdown
```

<sub>Reviews (4) · Last reviewed commit: ["fix(nesinit): readiness is a
socket
that..."](731d34df9d)</sub>

<!-- /greptile_comment -->

---------

Co-authored-by: DatCaptainHorse <DatCaptainHorse@users.noreply.github.com>
Co-authored-by: Claude Opus 5 <noreply@anthropic.com>

build/etc/profile.d/nestri-env.sh

@@ -14,14 +14,22 @@ if [ "$(id -u)" = "1000" ]; then
     export XDG_SESSION_TYPE="${XDG_SESSION_TYPE:-wayland}"
     export XDG_SESSION_DESKTOP="${XDG_SESSION_DESKTOP:-nestri}"
 
-    # Ensure proper VAAPI driver is used
-    #export LIBVA_DRIVER_NAME="radeonsi"
-
-    # Force zink usage for OpenGL -> Vulkan translation
-    #export __GLX_VENDOR_LIBRARY_NAME=mesa
-    #export MESA_LOADER_DRIVER_OVERRIDE=zink
-    #export GALLIUM_DRIVER=zink
 
     # Ensure standard XDG dirs exist
     mkdir -p "${XDG_CONFIG_HOME}" "${XDG_DATA_HOME}" "${XDG_CACHE_HOME}" "${XDG_STATE_HOME}" 2>/dev/null || true
 fi
+
+# OpenGL -> Vulkan, for anybody who reaches a shell in here.
+#
+# Outside the uid test above on purpose, and duplicated from the init on
+# purpose. This file is only ever read by a person who got a shell in a box --
+# nothing a box runs is started from a login, so every service and every
+# workload is exec'd with a cleared environment and never sees this. The init
+# sets the same three for what it starts.
+#
+# It is here so that a debug shell renders the way a session does. A shell that
+# silently has no GL driver is how somebody concludes the image is broken while
+# the image is fine.
+export __GLX_VENDOR_LIBRARY_NAME=mesa
+export MESA_LOADER_DRIVER_OVERRIDE=zink
+export GALLIUM_DRIVER=zink