build: chromium, font-noto and postgresql-client for the browser gates

zegit's `browser tests` (chromedp + CDP virtual authenticator) and
`lighthouse` jobs were github.com-only, so when `ci` was routed to this
runner on 2026-08-31 they stopped running anywhere. Chromium 149 (Alpine
3.23) with font-noto lets both run here; psql lets the lighthouse job
create and drop its own database on ci-postgres instead of migrating the
shared maintenance database from under the integration suite's template.

Verified locally (docker build, amd64): chromium-browser 149.0.7827.53,
psql 18.6, 45 font files, node 24.18.1, still uid 1000.

.github/workflows/build-image.yml

@@ -109,6 +109,22 @@ jobs:
       # missing tool, blocking v0.0.134 and v0.0.135. The list only covers what
       # someone remembered to add, so add to it whenever a gate grows a new
       # shell dependency.
+      #
+      # DERIVED once, 2026-08-31, rather than remembered: every command invoked
+      # from a `run:` block across zegit's Gitea-executed workflows and its
+      # composite actions was extracted and checked against this list. Result:
+      # no missing apk package. Everything resolved to one of three sources —
+      # baked in here; provided by busybox/coreutils; or downloaded per-run and
+      # immediately version-checked (go via setup-go, buildctl, flux, cosign,
+      # syft, goreleaser). The download path needs nothing from this image
+      # beyond curl and tar, both already asserted.
+      #
+      # What the audit DID find is that the busybox/coreutils layer was entirely
+      # unasserted, so dropping `coreutils` from the apk line above would pass
+      # this check while base64, mktemp, seq and sort silently vanished — and by
+      # the history above, their absence would be narrated as whatever the gate
+      # using them happened to be doing. They are asserted below now. They are
+      # cheap to check and the failure they prevent is expensive to read.
       - name: Verify the image still contains the toolchain the gates need
         if: ${{ steps.meta.outputs.push == 'true' }}
         run: |
@@ -129,6 +145,11 @@ jobs:
               command -v tar      >/dev/null && echo "tar=ok"      || echo "tar=MISSING"
               command -v openssl  >/dev/null && echo "openssl=ok"  || echo "openssl=MISSING"
               command -v jq       >/dev/null && echo "jq=ok"       || echo "jq=MISSING"
+              # busybox/coreutils layer: used across zegit's gates for base64
+              # decoding of DSSE payloads, temp dirs, poll loops and sorting.
+              for t in base64 mktemp seq sort sed grep cut head wc uname date; do
+                command -v "$t" >/dev/null && echo "$t=ok" || echo "$t=MISSING"
+              done
               [ -x "$(git --exec-path)/git-http-backend" ] \
                 && echo "git-http-backend=ok" || echo "git-http-backend=MISSING"
             ' 2>&1) || { echo "::error::could not run $REF on $plat"; fail=1; continue; }

Dockerfile

@@ -58,6 +58,19 @@ USER root
 #             validate-admission.sh and feature-lint.sh all shell out to
 #             python3, and credentials-coverage parses manifests with yaml
 #
+# chromium, font-noto -> the browser gates (2026-09-08): zegit's `browser
+#             tests` (chromedp + a CDP virtual authenticator over the WebAuthn
+#             ceremony pages) and `lighthouse` (treosh/lighthouse-ci-action
+#             via chrome-launcher) were github.com-only jobs, so when `ci`
+#             was routed to this runner on 2026-08-31 they stopped running
+#             anywhere. chromedp finds `chromium`/`chromium-browser` on PATH;
+#             chrome-launcher honours CHROME_PATH. font-noto so text renders
+#             (an empty font set makes layout/contrast audits meaningless).
+# postgresql-client -> `psql`, so the lighthouse job can CREATE/DROP its own
+#             database on the runner's ci-postgres (ZEGIT_TESTPG_DSN) instead
+#             of migrating the shared maintenance database from under the
+#             integration suite's template.
+#
 # Go is intentionally NOT baked in: actions/setup-go fetches the pinned version
 # per-run (node + tar are present), so the image needs no rebuild on Go bumps.
 RUN apk add --no-cache \
@@ -75,7 +88,10 @@ RUN apk add --no-cache \
       python3 \
       py3-yaml \
       openssl \
-      jq
+      jq \
+      chromium \
+      font-noto \
+      postgresql-client
 
 # Match the runner pod's runAsUser (1000); keep the image non-root by default.
 USER 1000