Multi-version builds via Stonecutter + concurrent launch tests for every supported Minecraft version

.github/scripts/generate-matrices.sh

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+#!/usr/bin/env bash
+# Derives the CI job matrices from supported-versions.json (the single source
+# of truth for supported Minecraft versions) and writes them to GITHUB_OUTPUT:
+#  - build:  one entry per build variant       -> { mc, java }
+#  - launch: one entry per launchable version  -> { mc, java, pregen_world }
+# pregen_world marks versions whose Fabric API has no client gametest module;
+# their launch test needs a pre-generated world (see generate-test-world.sh).
+set -euo pipefail
+
+JSON=supported-versions.json
+
+java_for_variant() {
+	grep -oP '^java_version=\K.+' "versions/$1/gradle.properties"
+}
+
+launch="[]"
+while IFS=$'\t' read -r mc variant gametest; do
+	java="$(java_for_variant "$variant")"
+	pregen=$([ "$gametest" = "false" ] && echo true || echo false)
+	launch="$(jq -c --arg mc "$mc" --arg java "$java" --argjson pregen "$pregen" \
+		'. + [{mc: $mc, java: $java, pregen_world: $pregen}]' <<<"$launch")"
+done < <(jq -r 'to_entries[] | [.key, .value.variant, (.value.clientGametest | tostring)] | @tsv' "$JSON")
+
+build="[]"
+while read -r variant; do
+	java="$(java_for_variant "$variant")"
+	build="$(jq -c --arg mc "$variant" --arg java "$java" \
+		'. + [{mc: $mc, java: $java}]' <<<"$build")"
+done < <(jq -r '[.[].variant] | reduce .[] as $v ([]; if index($v) then . else . + [$v] end) | .[]' "$JSON")
+
+echo "build=$build" >> "$GITHUB_OUTPUT"
+echo "launch=$launch" >> "$GITHUB_OUTPUT"
+echo "build matrix:  $build"
+echo "launch matrix: $launch"

.github/scripts/generate-test-world.sh

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+#!/usr/bin/env bash
+# Generates a vanilla singleplayer world save for the given Minecraft version
+# by briefly running that version's dedicated server, and places it where the
+# launch test expects it (launchtest/run/saves/ci-world).
+#
+# Only needed for versions whose Fabric API has no client gametest module
+# (before 1.21.4): their launch test cannot create a world in-game, so the
+# client auto-joins this save via --quickPlaySingleplayer instead. Using the
+# exact same Minecraft version to generate the world avoids any world-upgrade
+# prompts when the client opens it.
+set -euo pipefail
+
+MC_VERSION="${1:?usage: generate-test-world.sh <minecraft-version>}"
+DEST="$(pwd)/launchtest/run/saves/ci-world"
+
+WORK="$(mktemp -d)"
+cd "$WORK"
+
+MANIFEST_URL="$(curl -sSf https://piston-meta.mojang.com/mc/game/version_manifest_v2.json \
+	| jq -r --arg v "$MC_VERSION" '.versions[] | select(.id == $v) | .url')"
+SERVER_URL="$(curl -sSf "$MANIFEST_URL" | jq -r '.downloads.server.url')"
+curl -sSfo server.jar "$SERVER_URL"
+
+echo "eula=true" > eula.txt
+# A flat world keeps generation fast and renders instantly on the CI software
+# renderer. The default gamemode (survival) matches the gametest-based runs.
+cat > server.properties <<'EOF'
+level-name=ci-world
+level-type=minecraft\:flat
+view-distance=4
+simulation-distance=4
+online-mode=false
+spawn-protection=0
+EOF
+
+mkfifo console
+java -Xmx1G -jar server.jar nogui < console > server-log.txt 2>&1 &
+SERVER_PID=$!
+exec 3> console
+
+for _ in $(seq 1 300); do
+	grep -q 'Done (' server-log.txt && break
+	if ! kill -0 "$SERVER_PID" 2>/dev/null; then
+		cat server-log.txt
+		echo "::error::Dedicated server for $MC_VERSION exited before finishing world generation" >&2
+		exit 1
+	fi
+	sleep 1
+done
+if ! grep -q 'Done (' server-log.txt; then
+	cat server-log.txt
+	echo "::error::Dedicated server for $MC_VERSION did not finish starting within 300s" >&2
+	exit 1
+fi
+
+echo "stop" >&3
+wait "$SERVER_PID"
+exec 3>&-
+
+mkdir -p "$(dirname "$DEST")"
+cp -r ci-world "$DEST"
+echo "Generated test world at $DEST"

.github/scripts/publish-screenshots.sh

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+#!/usr/bin/env bash
+# Collects the launch-test screenshots uploaded as artifacts by every matrix
+# job of the current workflow run, normalizes their names, and commits them to
+# the ci-screenshots branch so they can be embedded (as raw.githubusercontent
+# URLs) in a PR comment and in the job summary.
+#
+# Leaves the normalized screenshots in screenshots-publish/ for the comment
+# step: <sha>/mc-<version>-survival.png and <sha>/mc-<version>-title.png.
+#
+# Required env: GITHUB_TOKEN, GITHUB_REPOSITORY, GITHUB_RUN_ID, GITHUB_SHA
+set -euo pipefail
+
+api() {
+	curl -sSf -H "Authorization: Bearer $GITHUB_TOKEN" -H "Accept: application/vnd.github+json" "$@"
+}
+
+# --- Download every launch-screenshots-mc* artifact of this run -------------
+mkdir -p artifact-zips shots
+api "https://api.github.com/repos/$GITHUB_REPOSITORY/actions/runs/$GITHUB_RUN_ID/artifacts?per_page=100" > artifacts.json
+
+while IFS=: read -r id name; do
+	mc="${name#launch-screenshots-mc}"
+	echo "Downloading $name"
+	curl -sSfL -H "Authorization: Bearer $GITHUB_TOKEN" \
+		-o "artifact-zips/$id.zip" \
+		"https://api.github.com/repos/$GITHUB_REPOSITORY/actions/artifacts/$id/zip"
+	mkdir -p "shots/$mc"
+	unzip -oq "artifact-zips/$id.zip" -d "shots/$mc"
+done < <(jq -r '.artifacts[] | select(.name | startswith("launch-screenshots-mc")) | "\(.id):\(.name)"' artifacts.json)
+
+# --- Normalize names (gametest screenshots carry a timestamp prefix) --------
+PUBLISH="screenshots-publish/$GITHUB_SHA"
+mkdir -p "$PUBLISH"
+
+for dir in shots/*/; do
+	mc="$(basename "$dir")"
+	for kind in survival-world title-screen; do
+		src="$(find "$dir" -name "*betterhud-$kind.png" -print -quit)"
+		if [ -n "$src" ]; then
+			cp "$src" "$PUBLISH/mc-$mc-${kind%%-*}.png"
+		fi
+	done
+done
+
+count="$(find "$PUBLISH" -name '*.png' | wc -l)"
+echo "Collected $count screenshots"
+if [ "$count" -eq 0 ]; then
+	echo "No screenshots to publish, skipping branch update"
+	exit 0
+fi
+
+# --- Commit to the ci-screenshots branch ------------------------------------
+REMOTE="https://x-access-token:${GITHUB_TOKEN}@github.com/${GITHUB_REPOSITORY}.git"
+if ! git clone --quiet --depth 1 --branch ci-screenshots "$REMOTE" ci-screenshots-branch 2>/dev/null; then
+	mkdir -p ci-screenshots-branch
+	git -C ci-screenshots-branch init --quiet -b ci-screenshots
+	git -C ci-screenshots-branch remote add origin "$REMOTE"
+fi
+
+mkdir -p "ci-screenshots-branch/$GITHUB_SHA"
+cp "$PUBLISH"/*.png "ci-screenshots-branch/$GITHUB_SHA/"
+cd ci-screenshots-branch
+git add .
+if git diff --cached --quiet; then
+	echo "Screenshots already published for $GITHUB_SHA"
+	exit 0
+fi
+git -c user.name="github-actions[bot]" -c user.email="41898282+github-actions[bot]@users.noreply.github.com" \
+	commit --quiet -m "CI screenshots for $GITHUB_SHA"
+
+# Retry the push in case a concurrent run updated the branch first.
+for _ in 1 2 3; do
+	if git push --quiet origin ci-screenshots; then
+		echo "Published screenshots to ci-screenshots/$GITHUB_SHA"
+		exit 0
+	fi
+	git pull --quiet --rebase origin ci-screenshots || true
+done
+echo "::error::Could not push screenshots to the ci-screenshots branch" >&2
+exit 1