diff --git a/.github/copilot-instructions.md b/.github/copilot-instructions.md
index 2a5c816..00c3b43 100644
--- a/.github/copilot-instructions.md
+++ b/.github/copilot-instructions.md
@@ -1,5 +1,32 @@
 # Copilot Instructions
 
+## Prerequisites
+
+Requires **Java 21+** and **Apache Maven 3.9+**.
+
+If Maven is not installed, download and extract it (no admin required):
+
+```powershell
+# Download Maven 3.9.8
+Invoke-WebRequest -Uri "https://archive.apache.org/dist/maven/maven-3/3.9.8/binaries/apache-maven-3.9.8-bin.zip" -OutFile "$env:TEMP\maven.zip" -UseBasicParsing
+
+# Extract to .tools/ inside the repo (gitignored)
+Expand-Archive -Path "$env:TEMP\maven.zip" -DestinationPath ".tools" -Force
+
+# Add to PATH for the current session
+$env:PATH = "$PWD\.tools\apache-maven-3.9.8\bin;$env:PATH"
+```
+
+Verify with `mvn -version`.
+
+Note: `.mvn/jvm.config` includes `--add-opens` to suppress Maven reflection warnings. On Java 22+, additional harmless warnings from Maven's jansi/guava/sisu libraries may appear — these will be resolved in Maven 4.0.
+
+When running Maven in PowerShell, pipe through `Out-Host` to avoid stderr warnings showing as red errors:
+
+```powershell
+mvn package -DskipTests 2>&1 | Out-Host
+```
+
 ## Build & Test
 
 ```bash
diff --git a/.gitignore b/.gitignore
index bc58bba..67fcfb4 100644
--- a/.gitignore
+++ b/.gitignore
@@ -4,6 +4,9 @@ target/
 .settings/
 dependency-reduced-pom.xml
 
+# Local tool installs (Maven, etc.)
+.tools/
+
 # IDE
 *.iml
 .idea/
diff --git a/.mvn/jvm.config b/.mvn/jvm.config
new file mode 100644
index 0000000..e52faa7
--- /dev/null
+++ b/.mvn/jvm.config
@@ -0,0 +1 @@
+--add-opens=java.base/java.lang.reflect=ALL-UNNAMED
diff --git a/src/main/java/org/quetoo/installer/Manager.java b/src/main/java/org/quetoo/installer/Manager.java
index 8c32431..2914180 100644
--- a/src/main/java/org/quetoo/installer/Manager.java
+++ b/src/main/java/org/quetoo/installer/Manager.java
@@ -70,7 +70,7 @@ public Observable<Delta> delta(final Observable<Index> indices) {
    * @return An Observable yielding the synchronized files.
    */
   public Observable<File> sync(final Observable<Delta> deltas) {
-    return deltas.concatMap(delta -> delta.getIndex().getSync().sync(delta))
+    return deltas.flatMap(delta -> delta.getIndex().getSync().sync(delta))
         .doOnNext(file -> {
           if (file.getParentFile().equals(config.getBin())) {
             file.setExecutable(true);