base: bake agent-browser + Playwright Chromium (headless browsing, all variants)

Gives the agent a real browser it can drive so front-end work involving live
DOM/WebGL can be VERIFIED, not guessed. The agent-browser skill (from the
skillset repo) was a no-op without the binary; it now works out of the box.

- agent-browser CLI (standalone Rust, ships no browser) via npm, prefixed
  NPM_CONFIG_PREFIX=/usr so it survives the ~/.pi/npm-global volume.
- Chromium fetched with 'playwright install --with-deps chromium' into
  PLAYWRIGHT_BROWSERS_PATH=/usr/local/share/ms-playwright — a system path that
  the /home/developer volume can't shadow (unlike agent-browser's own
  ~/.agent-browser/browsers default, which WOULD vanish on recreate).
- Stable /usr/local/bin/agent-chrome symlink, exported as
  AGENT_BROWSER_EXECUTABLE_PATH, insulates the ENV from Playwright's
  per-version chromium-<rev> dir name.

Verified end-to-end (this session): agent-browser drives the baked Chromium
headless (open + title + screenshot + eval into a WebGL SPA); doctor launch
test passes in ~0.5s. Debian trixie --with-deps resolution verified (exit 0;
t64 lib renames handled). hadolint clean; check-base-hash OK (only *_VERSION
args added). Cost ~960 MB (Chromium + headless shell). Base-affecting →
rebuilds base-<hash> on next release.

Dockerfile.base

@@ -14,7 +14,7 @@
 # content-addressed over this file, so any byte change invalidates the
 # cache. Recommended cadence: once per release for security updates.
 #
-# BASE_REBUILD_DATE: 2026-07-11 (Unreleased — typst PDF engine + xz-utils + pandoc typst-template default-font patch)
+# BASE_REBUILD_DATE: 2026-07-13 (Unreleased — agent-browser CLI + Playwright Chromium for headless browser automation; prior: typst PDF engine + xz-utils + pandoc typst-template default-font patch)
 #
 # ── Lineage note ─────────────────────────────────────────────────────
 # Adapted from opencode-devbox/Dockerfile.base (commit before v1.16.2).
@@ -457,6 +457,52 @@ RUN curl -fsSL --retry 5 --retry-delay 5 --retry-all-errors https://deb.nodesour
     apt-get install -y --no-install-recommends nodejs && \
     rm -rf /var/lib/apt/lists/*
 
+# ── agent-browser — headless browser automation for the agent ────────
+# Gives the agent a real browser it can drive (open/click/fill/eval/
+# screenshot) so front-end work involving live DOM or WebGL can be VERIFIED
+# rather than guessed at. The `agent-browser` skill (shipped from the
+# skillset repo, not this image) documents the CLI; without this block that
+# skill is a no-op because the binary isn't present. Verified end-to-end
+# 2026-07-13: drives the baked Chromium headless (open + screenshot + eval
+# into a WebGL SPA) — doctor's launch test passes in ~0.5s.
+#
+# TWO pieces, because agent-browser is a standalone Rust CLI that ships NO
+# browser of its own — it only drives one you provide:
+#   1. the CLI itself (npm; ~70 MB of prebuilt native binaries), and
+#   2. a Chromium, which we fetch via Playwright.
+#
+# Why Playwright fetches the browser (and NOT `agent-browser install`):
+# agent-browser's own installer drops Chrome under ~/.agent-browser/browsers
+# — inside /home/${USER_NAME}, which is a NAMED VOLUME at runtime, so a
+# build-time download would be SHADOWED (invisible) once the volume mounts.
+# Playwright honours PLAYWRIGHT_BROWSERS_PATH, so we place the browser under
+# /usr/local/share (never shadowed) and hand agent-browser a STABLE symlink
+# via AGENT_BROWSER_EXECUTABLE_PATH — the symlink insulates the ENV from
+# Playwright's per-version `chromium-<rev>` directory name (glob picks the
+# real headful build; the `chromium_headless_shell-*` dir has an underscore
+# so `chromium-*` never matches it).
+#
+# `playwright install --with-deps chromium` also apt-installs Chromium's
+# runtime libs; verified to resolve correctly on Debian trixie (exit 0 — the
+# t64 library renames are handled by Playwright's dep list). Build runs as
+# root, so the apt step works. NPM_CONFIG_PREFIX=/usr keeps both CLIs on /usr
+# so they survive the ~/.pi/npm-global volume mount (same trick the variant
+# uses for pi). Cost: ~960 MB (Chromium + headless shell) — the bulk of the
+# base's browser footprint; the one real tradeoff of shipping this everywhere.
+ARG AGENT_BROWSER_VERSION=latest
+ARG PLAYWRIGHT_VERSION=latest
+ENV PLAYWRIGHT_BROWSERS_PATH=/usr/local/share/ms-playwright
+RUN NPM_CONFIG_PREFIX=/usr npm install -g \
+      "agent-browser@${AGENT_BROWSER_VERSION}" \
+      "playwright@${PLAYWRIGHT_VERSION}" && \
+    playwright install --with-deps chromium && \
+    for chrome in "${PLAYWRIGHT_BROWSERS_PATH}"/chromium-*/chrome-linux/chrome; do \
+      ln -sf "$chrome" /usr/local/bin/agent-chrome; break; \
+    done && \
+    agent-browser --version && \
+    test -x "$(readlink -f /usr/local/bin/agent-chrome)"
+ENV AGENT_BROWSER_EXECUTABLE_PATH=/usr/local/bin/agent-chrome
+
 # ── tldr (tealdeer) — community-maintained command examples ──────────
 # Tealdeer is a Rust port of the tldr-pages client; ~5 MB static binary,
 # ~135 MB smaller than the Node tldr global. Same `tldr` command, same UX.