Bake the browser's runtime libraries into the base image

`npx playwright install chromium` downloaded ~150 MB of browser that then
died with "error while loading shared libraries: libglib-2.0.so.0" —
verified, not inferred, against the current image. The image shipped none
of Chromium's shared libraries, which is why `apt install
google-chrome-stable` looked like the cure: apt was quietly installing the
same set as Chrome's own dependencies.

Installing them at runtime instead converges on the worst possible state.
The libraries land in the container's writable layer, so they are re-paid
after every Reset and *lost* on base-image migration, which replays apt
from a manifest. The browsers ride in ~/.cache/ms-playwright, inside the
home volume, and survive both — leaving a 400 MB browser present with its
libraries gone. So the libraries are baked and the browsers are not: each
half now lives where it already persists.

The layer runs `npx --yes playwright@latest install-deps chromium` rather
than a hand-written apt list. Ubuntu 24.04's 64-bit-time_t transition
renamed a swathe of these packages (libasound2t64, libatk1.0-0t64,
libglib2.0-0t64, …) and a new Chromium dependency would drift straight back
into the launch failure this exists to prevent; letting Playwright name its
own dependencies is self-maintaining. It sits immediately after Node — npx
is its only prerequisite — and well above the shim COPYs, so editing a shim
does not re-run it.

The `--dry-run` that follows is a build-time assertion, not decoration: on a
platform Playwright has no list for, `install-deps` prints a warning and
returns having installed **nothing, with exit status 0**. Without the
assertion that ships a broken image behind a clean build log.

Measured, on a build of this file with the layer applied over an otherwise
identical image: +99 packages, +334 MiB unpacked and +119 MiB compressed
(2950 → 3284 MiB, 759 → 878 MiB). Two thirds of that is not reachable by
trimming — libgbm1, which Chromium needs, pulls mesa-libgallium, which
pulls libllvm20. A chromium-only apt list measures 247 MiB against
install-deps' 341 MiB; the ~94 MiB difference is xvfb and the CJK/emoji
fonts, kept because the base ships no fonts at all and every page this
feature exists to display would otherwise render as tofu.

Verified on real builds, both architectures: a `--platform linux/arm64`
build of this file installs the same 99 packages and passes the same
assertion. On the new amd64 image, `playwright install chromium` with no
`--with-deps` and no `install-deps` launches headless Chromium 151.0.7922.34
and loads a page; on the old image the identical script fails on
libglib-2.0.so.0.

`install.rs` no longer runs `install-deps` unconditionally — that would be a
minutes-long apt run for nothing on a current image. It asks
`install-deps --dry-run` first and skips the install when everything is
present, saying which of the two happened on the progress stream. The check
is Playwright's rather than a probe of our own for library names, so check
and fix cannot disagree about what the dependency set is. Note that
`--dry-run` exits 0 both when everything is installed and when Playwright
has no list for the platform, so the verdict is read from its output.

Containers on older images stay the normal case until people migrate, and
they still work: on such an image the simulation cannot even resolve the
package names (the index is cleaned in every base image), which reports as
"couldn't tell" and installs — the right answer.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KSP2KNPhuWKQ4DL5TZEn3k

README.md

@@ -386,4 +386,24 @@ Users can override this in Settings via the global `docker_socket_path` option.
 
 **Shims**: `xclip`/`xsel`/`pbcopy` (OSC 52 clipboard forwarding), `xdg-open`/`sensible-browser`/`www-browser`/`x-www-browser`/`$BROWSER` (OSC 7777 URL relay to the host browser), `rec`/`arecord` (audio FIFO for voice mode)
 
+**Browser runtime libraries**: the shared libraries Chromium links against (`libnss3`, `libgbm1`,
+`libatk*`, `libasound2t64`, `libcups2t64`, `libpango`, `libdrm2`, … plus fonts) are baked in, via
+`npx playwright install-deps chromium` at build time. Without them `playwright install chromium`
+downloads a browser that then dies at launch with *"Host system is missing dependencies:
+libnss3.so"* — which is why installing `google-chrome-stable` used to look like the fix (apt was
+pulling the libraries in as *its* dependencies). Measured cost of the layer: +99 packages,
+**+334 MiB unpacked / +119 MiB compressed** (2950 → 3284 MiB unpacked, 759 → 878 MiB compressed).
+Two thirds of that is not avoidable by trimming — `libgbm1`, which Chromium needs, depends on
+`mesa-libgallium`, which depends on `libllvm20`. The list is taken from Playwright rather than
+hand-written so it cannot rot against Ubuntu 24.04's `t64` renames or a future Chromium dependency,
+and the `install-deps --dry-run` that follows it is a build-time assertion: on a platform
+Playwright has no list for, `install-deps` installs nothing and still exits 0.
+
+**Browser binaries are deliberately not baked.** They are large, they are version-coupled to
+whatever Playwright the user installs, and they already persist: `~/.cache/ms-playwright` is inside
+the home volume, so a downloaded browser survives container recreation *and* base-image migration.
+The libraries are the opposite — a runtime `apt-get install` lands in the container's writable
+layer, is re-paid after every Reset, and is lost on migration (which replays apt from a manifest
+against the new base). Baking one and not the other puts each half where it already persists.
+
 **Default user**: `claude` (UID/GID 1000, remapped by entrypoint to match host)