add ui tests to ci

Dockerfile

@@ -2,7 +2,8 @@
 # to ../resources/public/js (see ui/shadow-cljs.edn), i.e. /build/resources/public/js here.
 # trixie, not bookworm: its default-jre is Java 21, which shadow-cljs's Closure Compiler
 # requires (bookworm's is 17 -> UnsupportedClassVersionError).
-FROM node:22-trixie-slim AS ui
+# ui-base holds what the UI's release build and its tests share: the toolchain and the deps.
+FROM node:22-trixie-slim AS ui-base
 
 RUN apt-get update \
     && apt-get install -y --no-install-recommends default-jre-headless \
@@ -14,9 +15,20 @@ RUN npm ci
 # Resolve the ClojureScript deps in their own layer so source edits don't re-download them.
 COPY ui/shadow-cljs.edn ./
 RUN npx shadow-cljs classpath > /dev/null
+
+FROM ui-base AS ui
 COPY ui/src ./src
 RUN npx shadow-cljs release app
 
+# The UI's tests, not part of the server image: `docker build --target ui-test`
+# (script/docker-ui-test, script/docker-ui-coverage). Running the container runs the tests;
+# `npm run coverage` (script/docker-ui-coverage) also writes the report to /build/target/coverage/ui.
+FROM ui-base AS ui-test
+COPY ui/.c8rc.json ./
+COPY ui/src ./src
+COPY ui/test ./test
+CMD ["npm", "test"]
+
 # Stage 2: the server.
 # JDK 21+ is required by the MCP server (plumcp runs on virtual threads).
 FROM clojure:temurin-21-tools-deps