chromium-fourier NEXT.md: hit the clang 22 vs 147 wall

First-build summary on chromium-builder@boltzmann. gn gen succeeds
with our V4L2VDA-unlock args. ninja fails immediately on:

1. chromium 147 emits clang flags (-fno-lifetime-dse,
   -fsanitize-ignore-for-ubsan-feature=array-bounds) that clang 22
   doesn't know. Arch Linux ARM is on clang 22; clang 23 hasn't
   landed in extra yet.
2. Bundled x86_64 esbuild is invoked via qemu-x86_64-static but
   /lib64/ld-linux-x86-64.so.2 isn't installed — same shape as the
   bundled node-linux-x64 issue we already fixed by symlinking to
   system node. Smaller wall.

Documents 5 paths forward (grind patches / pin chromium 132 (7Ji's
known-good) / pin 138-141 middle ground / use chromium's bundled
clang / wait for Arch ARM clang 23) with estimated effort and trade-
offs. Recommends pinning to a chromium version that compiles clean
against clang 22 as the fastest path to a working browser, then
bumping as Arch ARM bumps clang.

Build host state preserved — container running, source extracted,
gn-gen'd, no compile artifacts. Easy to resume from any of the five
paths.

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

arch/chromium-fourier/NEXT.md

@@ -0,0 +1,110 @@
+# chromium-fourier — first-build status (2026-04-26 00:42 UTC)
+
+## Where we are
+
+Build environment: **chromium-builder LXD container on boltzmann**
+(8 cores, 28 GB RAM cap, 824 GB NVMe, Beryllium OS rkr3 host kernel).
+Source: chromium-147.0.7727.116 release tarball extracted at
+`/build/chromium/src` (25 GB extracted).
+
+`gn gen out/Default` **succeeds** with our 7Ji-style args
+(`use_v4l2_codec=true use_v4lplugin=true use_linux_v4l2_only=true
+use_vaapi=false`, system toolchain via `unbundle:default`, system clang
+at `/usr/bin/clang`, version-symlink `/usr/lib/clang/23` →
+`/usr/lib/clang/22`, compiler-rt-adjust-paths style suffix patch
+manually applied). 28057 targets generated.
+
+`ninja -C out/Default chrome` **fails immediately** with two distinct walls:
+
+### Wall 1 — clang version mismatch (chromium 147 ↔ Arch clang 22)
+
+Chromium 147's compile flags include
+`-fno-lifetime-dse` and
+`-fsanitize-ignore-for-ubsan-feature=array-bounds`. Both are clang 23+
+features. Arch Linux ARM ships **clang 22.1.3** (extra repo). Every
+single C++ compile fails with `clang++: error: unknown argument`.
+
+Resolutions, in order of effort:
+
+- **(a)** Wait for Arch ARM to bump clang to 23. Tracking package
+  upstream — happens whenever LLVM 23 lands in extra. Days to weeks.
+- **(b)** Use chromium's bundled clang via
+  `tools/clang/scripts/update.py`. That hits the same CIPD/gs://
+  "linux-arm64 isn't a first-class target" issue we saw with
+  `gclient sync` earlier — chromium's clang prebuilts are x86_64-only
+  for many platforms.
+- **(c)** Fork an older chromium (e.g., 132 or 138) that compiles
+  cleanly with clang 22. 7Ji's chromium-mpp PKGBUILD targets 132 and
+  builds clean on Arch ARM today. Loses 15 versions of upstream
+  chromium evolution but ships fast.
+- **(d)** Patch chromium 147 to drop the offending flags
+  (`build/config/compiler/BUILD.gn` has the cflags lists). 50–200 line
+  patch, brittle across version bumps but tractable. Fights every
+  rebase.
+
+### Wall 2 — bundled x86_64 esbuild under qemu
+
+After Wall 1 (or independently for Action targets):
+`qemu-x86_64-static: Could not open '/lib64/ld-linux-x86-64.so.2'`
+when chromium runs the bundled x86_64 `esbuild` from
+`third_party/devtools-frontend/.../scripts/build/typescript/ts_library.py`.
+Same shape as the bundled `node-linux-x64` issue we already fixed (we
+symlinked system node into that path). `esbuild` needs the same
+treatment — install system esbuild via `npm install -g esbuild` and
+symlink it into the path chromium expects. Or install `qemu-user-static`
++ `glibc-x86_64` to make the bundled binary actually run.
+
+**Wall 2 is much smaller than Wall 1** — a handful of bundled-x86_64
+binaries to identify and replace, vs. fundamental clang version mismatch.
+
+## What worked
+
+- LXD container provisioning on boltzmann via his recommendation —
+  the host environment is right.
+- Tarball-instead-of-gclient approach — sidesteps CIPD-doesn't-have-
+  linux-arm64 problem for source acquisition, leaves only a few
+  bundled binary issues at build time.
+- Wall 1 / Wall 2 are both **identifiable and bounded**. We're past
+  the "is this even doable" phase; this is now down to grinding the
+  patches.
+
+## Options — needs your call
+
+1. **Grind through Wall 1 with patches** — patch
+   `build/config/compiler/BUILD.gn` to drop flags clang 22 doesn't
+   know. Iterate per build error. Estimated 5–15 patch-and-retry
+   cycles to compile clean. Then 6–10 h actual build.
+2. **Pin to chromium 132** — match 7Ji's known-working version on
+   Arch ARM. Drop our STUDY focus on "current upstream Chromium" and
+   ship a 1-year-old binary. Build should work much sooner.
+3. **Pin to chromium 138 or 140** — middle ground. Likely uses clang
+   22 features and not 23. Some research needed to find the cutover.
+4. **Use chromium's bundled clang** — not viable on linux-arm64
+   without extensive sysroot setup; same CIPD issue as gclient sync.
+5. **Wait for Arch ARM clang 23** — passive, days-to-weeks horizon.
+
+Recommended (FWIW): **start with (3)** — find the latest chromium
+version that builds clean against clang 22 (probably 138-141 range),
+ship that as `chromium-fourier`, then bump as Arch ARM bumps clang.
+That gives us a working browser in a few hours rather than days, on
+mainline Linux + Wayland + V4L2 unlock — which is the actual goal.
+The "current upstream Chromium" requirement was nice-to-have, not
+essential.
+
+## State of the build host (preserved)
+
+- Container: `chromium-builder` on boltzmann (running, idle)
+- Source: `/build/chromium/src` (extracted tarball, 25 GB)
+- Build dir: `/build/chromium/src/out/Default` (gn-gen'd, no artifacts)
+- Tools installed: gn, ninja, clang 22, lld, gperf, nodejs (system),
+  rust, qt5/6, all the gtk/wayland/va/v4l deps from the long pacman
+  shopping list
+- Patches applied to source: `compiler-rt-adjust-paths` style (manual)
+- Symlinks: `/usr/lib/clang/23` → `/usr/lib/clang/22`,
+  `third_party/node/linux/node-linux-x64/bin/node` → `/usr/bin/node`
+- Service unit history: `chromium-fetch.service` (one-shot, succeeded
+  on tarball + extract); `chromium-build.service` (one-shot, three
+  failed attempts above).
+
+Discard the container and start over with option 2 if you pick that
+direction; otherwise iterate from current state.