Improve MCC testing workflow resilience

tools/start-server.sh

@@ -1,12 +1,38 @@
 #!/bin/bash
 # Start a Minecraft server in a tmux session with named pipe for stdin
 # Servers live under $MCC_SERVERS or default to MinecraftOfficial/downloads/<version>/.
+resolve_java_bin() {
+    if command -v java >/dev/null 2>&1 && java -version >/dev/null 2>&1; then
+        command -v java
+        return 0
+    fi
+
+    local candidate
+    for candidate in \
+        "${JAVA_BIN:-}" \
+        "/opt/homebrew/opt/openjdk/bin/java" \
+        "/usr/local/opt/openjdk/bin/java" \
+        "/usr/lib/jvm/default-java/bin/java"
+    do
+        [[ -z "$candidate" ]] && continue
+        if [[ -x "$candidate" ]]; then
+            if "$candidate" -version >/dev/null 2>&1; then
+                printf '%s\n' "$candidate"
+                return 0
+            fi
+        fi
+    done
+
+    return 1
+}
+
 VERSION="${1}"
 REPO_ROOT="$(cd "$(dirname "$0")/.." && pwd)"
 DOWNLOADS="${MCC_SERVERS:-$REPO_ROOT/MinecraftOfficial/downloads}"
 DIR="$DOWNLOADS/$VERSION"
 PIPE="$DIR/stdin.pipe"
 SESSION="mc-${VERSION//\./_}"
+JAVA_BIN="$(resolve_java_bin || true)"
 
 if [ -z "$VERSION" ] || [ ! -d "$DIR" ]; then
     echo "Error: Server directory not found${VERSION:+: $DIR}"
@@ -20,6 +46,16 @@ if [ ! -f "$DIR/server.jar" ]; then
     exit 1
 fi
 
+if ! command -v tmux >/dev/null 2>&1; then
+    echo "Error: tmux is required to start local test servers"
+    exit 1
+fi
+
+if [[ -z "$JAVA_BIN" ]]; then
+    echo "Error: Java was not found on PATH. Install Java or set JAVA_BIN." >&2
+    exit 1
+fi
+
 if tmux has-session -t "$SESSION" 2>/dev/null; then
     echo "Server $VERSION already running in tmux session '$SESSION'"
     echo "View output:  tmux capture-pane -t '$SESSION' -p -S -50"
@@ -29,10 +65,14 @@ fi
 
 rm -f "$DIR/world/session.lock"
 
+if [[ -e "$PIPE" && ! -p "$PIPE" ]]; then
+    rm -f "$PIPE"
+fi
+
 [ -p "$PIPE" ] || mkfifo "$PIPE"
 
 tmux new-session -d -s "$SESSION" -c "$DIR" \
-  "tail -f $PIPE | java -Xmx2G -Xms2G -jar server.jar nogui 2>&1"
+  "tail -f $PIPE | '$JAVA_BIN' -Xmx2G -Xms2G -jar server.jar nogui 2>&1"
 
 echo "Server $VERSION started in tmux session '$SESSION'"
 echo "Send commands: echo 'say hello' > $PIPE"