mesa-panvk-bifrost: iter10 polish — drop sandbox bypass, pin sha256, tighten loader select

iter10 of the panvk-bifrost campaign. Eliminates the cosmetic
'--disable-gpu-sandbox' warning at brave-vulkan launch + pins the
Mesa tarball hash + makes the Vulkan ICD selection deterministic
across filesystems.

PKGBUILD changes (pkgrel: 1 -> 2):
  - install ICD JSON at /usr/share/vulkan/icd.d/00-panvk-bifrost.json
    (was: /usr/lib/panvk-bifrost/icd.json — required VK_ICD_FILENAMES,
    which the GPU sandbox would strip, forcing --disable-gpu-sandbox)
  - libvulkan_panfrost.so install path unchanged at /usr/lib/panvk-bifrost/
  - sha256sums[0] pinned to 1d3c3b8a8363b8cc354175bb4a684ad8b035211cc1d6fa17aeb9b9623c513f89
    (mesa-26.0.6.tar.xz from archive.mesa3d.org); patches + brave-vulkan +
    icd.json remain SKIP since they're in-tree (git-tracked)

brave-vulkan changes:
  - dropped --no-sandbox + --disable-gpu-sandbox: env vars MESA_VK_VERSION_OVERRIDE
    and PAN_I_WANT_A_BROKEN_VULKAN_DRIVER survive the GPU sandbox boundary
    (Mesa loader reads them pre-seccomp-lockdown)
  - dropped VK_ICD_FILENAMES (loader auto-picks via icd.d/ directory scan)
  - added VK_LOADER_DRIVERS_SELECT='00-panvk-bifrost*' for deterministic
    ICD selection — Vulkan loader's readdir order is implementation-defined
    per Khronos LoaderDriverInterface, so the '00-' filename prefix is
    not spec-backed (ext4 happens to give insertion-order, other filesystems
    may not). VK_LOADER_DRIVERS_SELECT short-circuits readdir ambiguity.
    (Phase 5 review hardening.)

Test result on ohm (pre-push validation):
  - brave-vulkan launches Brave without sandbox bypass
  - seccomp-bpf sandboxes activate normally for utility/renderer processes
  - 'panvk is not a conformant Vulkan implementation' fires ONCE (loader-select
    excluded stock ICD from enumeration — only patched driver loads)
  - GPU process boots, no 'Exiting GPU process' error
  - Brave runs through full test timeout cleanly

README updated to reflect the new install layout + simplified wrapper.

Campaign artifacts: ~/src/panvk-bifrost/{phase0_findings_iter10.md,
phase8_iteration9_close.md (which iter10 polishes)}.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

arch/mesa-panvk-bifrost/brave-vulkan

@@ -7,26 +7,35 @@
 #
 # Provided by the mesa-panvk-bifrost package. See:
 #   /usr/share/doc/mesa-panvk-bifrost/README
-#   ~/src/panvk-bifrost/phase8_iteration9_close.md (campaign close)
+#   ~/src/panvk-bifrost/phase8_iteration{9,10}_close.md
 #
 # Usage: brave-vulkan [brave args...]
 # Equivalent to: brave [VULKAN_FLAGS] [your args]
+#
+# iter10 changes vs iter9:
+#   - dropped VK_ICD_FILENAMES env (ICD now at /usr/share/vulkan/icd.d/
+#     with '00-' prefix so the Vulkan loader auto-picks ours first)
+#   - dropped --no-sandbox / --disable-gpu-sandbox (env vars survive the
+#     GPU sandbox boundary, no bypass needed)
 
 set -e
 
-# Patched Vulkan driver (from this package) — must point at the custom path
-# so we don't clash with the stock /usr/share/vulkan/icd.d/panfrost_icd.json
-export VK_ICD_FILENAMES=/usr/lib/panvk-bifrost/icd.json
+# Pin the Vulkan ICD selection to our package's ICD. The Vulkan loader's
+# readdir-order in /usr/share/vulkan/icd.d/ is implementation-defined
+# per Khronos LoaderDriverInterface — the '00-' filename prefix is NOT
+# spec-backed. VK_LOADER_DRIVERS_SELECT short-circuits the directory
+# enumeration and picks our ICD deterministically. (Phase 5 review
+# hardening, iter10.)
+export VK_LOADER_DRIVERS_SELECT='00-panvk-bifrost*'
 
 # PanVk's "I know it's not conformant" gate — the patched driver still
-# refuses to enumerate Bifrost without this env var (Mesa upstream choice,
-# kept for compatibility).
+# refuses to enumerate Bifrost without this env var (upstream Mesa choice
+# for v6/v7, kept for compatibility).
 export PAN_I_WANT_A_BROKEN_VULKAN_DRIVER=1
 
 # Override apiVersion to 1.2 — ANGLE (Chromium's GL stack) requires
-# device.apiVersion >= 1.1. The patched libvulkan_panfrost.so still has
-# a PAN_ARCH>=10 gate inside get_api_version(); easier to override at
-# runtime via this Mesa env var than to add a third patch.
+# device.apiVersion >= 1.1. Source patches don't move get_api_version()'s
+# PAN_ARCH>=10 hardcode; the env var override does.
 export MESA_VK_VERSION_OVERRIDE=1.2
 
 # Find the live Plasma session's Xauthority. On a fresh boot the suffix
@@ -55,7 +64,5 @@ exec brave \
     --enable-features=Vulkan \
     --use-vulkan=native \
     --ozone-platform=x11 \
-    --no-sandbox \
-    --disable-gpu-sandbox \
     --ignore-gpu-blocklist \
     "$@"