diff --git a/.github/scripts/VerifyMavenWrapperIntegrity.java b/.github/scripts/VerifyMavenWrapperIntegrity.java
new file mode 100644
index 00000000..bef0bd55
--- /dev/null
+++ b/.github/scripts/VerifyMavenWrapperIntegrity.java
@@ -0,0 +1,62 @@
+import java.io.IOException;
+import java.io.Reader;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.Properties;
+
+/**
+ * Fail-closed Maven Wrapper bootstrap preflight for GitHub Actions.
+ *
+ * <p>This source-file-mode utility runs on the JDK configured by the workflow before any
+ * {@code mvnw} or {@code mvnw.cmd} invocation. It verifies that the Maven distribution remains
+ * bound to the exact reviewed URL and SHA-256 checksum, so deleting or changing the checksum
+ * cannot silently bypass integrity verification before Maven starts.</p>
+ */
+public final class VerifyMavenWrapperIntegrity {
+
+    private static final String REVIEWED_WRAPPER_VERSION = "3.3.4";
+    private static final String REVIEWED_DISTRIBUTION_TYPE = "only-script";
+    private static final String REVIEWED_DISTRIBUTION_URL =
+            "https://repo.maven.apache.org/maven2/org/apache/maven/apache-maven/3.9.11/"
+                    + "apache-maven-3.9.11-bin.zip";
+    private static final String REVIEWED_DISTRIBUTION_SHA256 =
+            "0d7125e8c91097b36edb990ea5934e6c68b4440eef4ea96510a0f6815e7eeadb";
+
+    private VerifyMavenWrapperIntegrity() {
+    }
+
+    /**
+     * Validates the reviewed Maven Wrapper bootstrap inputs before Maven can execute.
+     *
+     * @param args ignored command-line arguments
+     * @throws IOException when the wrapper properties cannot be read
+     */
+    public static void main(String[] args) throws IOException {
+        Path propertiesPath = Path.of(".mvn", "wrapper", "maven-wrapper.properties");
+        if (!Files.isRegularFile(propertiesPath)) {
+            throw new IllegalStateException("Missing Maven Wrapper properties: " + propertiesPath);
+        }
+
+        Properties properties = new Properties();
+        try (Reader reader = Files.newBufferedReader(propertiesPath, StandardCharsets.UTF_8)) {
+            properties.load(reader);
+        }
+
+        requireExact(properties, "wrapperVersion", REVIEWED_WRAPPER_VERSION);
+        requireExact(properties, "distributionType", REVIEWED_DISTRIBUTION_TYPE);
+        requireExact(properties, "distributionUrl", REVIEWED_DISTRIBUTION_URL);
+        requireExact(properties, "distributionSha256Sum", REVIEWED_DISTRIBUTION_SHA256);
+        System.out.println("Maven Wrapper integrity preflight passed.");
+    }
+
+    private static void requireExact(Properties properties, String key, String expected) {
+        String actual = properties.getProperty(key);
+        if (!expected.equals(actual)) {
+            throw new IllegalStateException(
+                    "Maven Wrapper integrity preflight rejected " + key
+                            + ": expected reviewed value but found " + String.valueOf(actual)
+            );
+        }
+    }
+}
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index c9780487..f127b84f 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -38,13 +38,21 @@ jobs:
           java-version: "25"
           cache: maven
 
+      - name: Verify Maven Wrapper integrity (Unix)
+        if: runner.os != 'Windows'
+        run: java .github/scripts/VerifyMavenWrapperIntegrity.java
+
       - name: Run tests (Unix)
         if: runner.os != 'Windows'
         run: ./mvnw -B test
 
+      - name: Verify Maven Wrapper integrity (Windows)
+        if: runner.os == 'Windows'
+        run: java .github/scripts/VerifyMavenWrapperIntegrity.java
+
       - name: Run tests (Windows)
         if: runner.os == 'Windows'
-        run: .\\mvnw.cmd -B test
+        run: .\mvnw.cmd -B test
 
   test_self_hosted:
     if: ${{ github.event_name == 'workflow_dispatch' && inputs.use_self_hosted == true }}
@@ -60,10 +68,18 @@ jobs:
           java-version: "25"
           cache: maven
 
+      - name: Verify Maven Wrapper integrity (Unix)
+        if: runner.os != 'Windows'
+        run: java .github/scripts/VerifyMavenWrapperIntegrity.java
+
       - name: Run tests (Unix)
         if: runner.os != 'Windows'
         run: ./mvnw -B test
 
+      - name: Verify Maven Wrapper integrity (Windows)
+        if: runner.os == 'Windows'
+        run: java .github/scripts/VerifyMavenWrapperIntegrity.java
+
       - name: Run tests (Windows)
         if: runner.os == 'Windows'
-        run: .\\mvnw.cmd -B test
+        run: .\mvnw.cmd -B test
diff --git a/.github/workflows/sbom.yml b/.github/workflows/sbom.yml
index 26aefe40..20f92d63 100644
--- a/.github/workflows/sbom.yml
+++ b/.github/workflows/sbom.yml
@@ -34,6 +34,9 @@ jobs:
           java-version: "25"
           cache: maven
 
+      - name: Verify Maven Wrapper integrity
+        run: java .github/scripts/VerifyMavenWrapperIntegrity.java
+
       - name: Generate CycloneDX SBOM (aggregate)
         run: ./mvnw -B -DskipTests org.cyclonedx:cyclonedx-maven-plugin:2.9.1:makeAggregateBom -DoutputFormat=all -Dcyclonedx.skipAttach=true
 
@@ -59,13 +62,21 @@ jobs:
           java-version: "25"
           cache: maven
 
+      - name: Verify Maven Wrapper integrity (Unix)
+        if: runner.os != 'Windows'
+        run: java .github/scripts/VerifyMavenWrapperIntegrity.java
+
       - name: Generate CycloneDX SBOM (aggregate)
         if: runner.os != 'Windows'
         run: ./mvnw -B -DskipTests org.cyclonedx:cyclonedx-maven-plugin:2.9.1:makeAggregateBom -DoutputFormat=all -Dcyclonedx.skipAttach=true
 
+      - name: Verify Maven Wrapper integrity (Windows)
+        if: runner.os == 'Windows'
+        run: java .github/scripts/VerifyMavenWrapperIntegrity.java
+
       - name: Generate CycloneDX SBOM (aggregate, Windows)
         if: runner.os == 'Windows'
-        run: .\\mvnw.cmd -B -DskipTests org.cyclonedx:cyclonedx-maven-plugin:2.9.1:makeAggregateBom -DoutputFormat=all -Dcyclonedx.skipAttach=true
+        run: .\mvnw.cmd -B -DskipTests org.cyclonedx:cyclonedx-maven-plugin:2.9.1:makeAggregateBom -DoutputFormat=all -Dcyclonedx.skipAttach=true
 
       - name: Upload SBOM artifact
         uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
diff --git a/.mvn/wrapper/maven-wrapper.properties b/.mvn/wrapper/maven-wrapper.properties
index c0bcafe9..222cba3b 100644
--- a/.mvn/wrapper/maven-wrapper.properties
+++ b/.mvn/wrapper/maven-wrapper.properties
@@ -1,3 +1,4 @@
 wrapperVersion=3.3.4
 distributionType=only-script
 distributionUrl=https://repo.maven.apache.org/maven2/org/apache/maven/apache-maven/3.9.11/apache-maven-3.9.11-bin.zip
+distributionSha256Sum=0d7125e8c91097b36edb990ea5934e6c68b4440eef4ea96510a0f6815e7eeadb
diff --git a/etl-service/src/test/java/com/xtrmetl/etl/documentation/MavenWrapperIntegrityTest.java b/etl-service/src/test/java/com/xtrmetl/etl/documentation/MavenWrapperIntegrityTest.java
new file mode 100644
index 00000000..a96dba72
--- /dev/null
+++ b/etl-service/src/test/java/com/xtrmetl/etl/documentation/MavenWrapperIntegrityTest.java
@@ -0,0 +1,183 @@
+package com.xtrmetl.etl.documentation;
+
+import org.junit.jupiter.api.Test;
+
+import java.io.IOException;
+import java.io.Reader;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.util.List;
+import java.util.Properties;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+/**
+ * Prevents Maven Wrapper bootstrap from executing an unverified Maven distribution.
+ *
+ * <p>The wrapper downloads Maven before project compilation and tests can run. This repository
+ * therefore treats the Maven distribution URL and its reviewed SHA-256 as one atomic build-input
+ * contract. A Maven version or URL change must carry a newly reviewed checksum in the same change;
+ * deleting the checksum must fail deterministically without network access.</p>
+ */
+class MavenWrapperIntegrityTest {
+
+    private static final String REVIEWED_DISTRIBUTION_URL =
+            "https://repo.maven.apache.org/maven2/org/apache/maven/apache-maven/3.9.11/"
+                    + "apache-maven-3.9.11-bin.zip";
+    private static final String REVIEWED_DISTRIBUTION_SHA256 =
+            "0d7125e8c91097b36edb990ea5934e6c68b4440eef4ea96510a0f6815e7eeadb";
+    private static final String PREFLIGHT_COMMAND =
+            "run: java .github/scripts/VerifyMavenWrapperIntegrity.java";
+
+    /**
+     * Requires the fixed Maven 3.9.11 download to remain bound to its reviewed SHA-256 checksum.
+     *
+     * @throws IOException when the wrapper properties cannot be read as repository source
+     */
+    @Test
+    void bindsMavenDistributionUrlToReviewedSha256() throws IOException {
+        Properties properties = new Properties();
+        Path wrapperProperties = projectRoot().resolve(
+                ".mvn/wrapper/maven-wrapper.properties"
+        );
+        assertTrue(Files.isRegularFile(wrapperProperties), "Maven Wrapper properties must exist");
+
+        try (Reader reader = Files.newBufferedReader(wrapperProperties, StandardCharsets.UTF_8)) {
+            properties.load(reader);
+        }
+
+        assertEquals("3.3.4", properties.getProperty("wrapperVersion"));
+        assertEquals("only-script", properties.getProperty("distributionType"));
+        assertEquals(
+                REVIEWED_DISTRIBUTION_URL,
+                properties.getProperty("distributionUrl"),
+                "Changing the Maven distribution requires review of a matching checksum"
+        );
+
+        String distributionSha256 = properties.getProperty("distributionSha256Sum");
+        assertNotNull(
+                distributionSha256,
+                "Maven Wrapper must verify the downloaded Maven distribution with SHA-256"
+        );
+        assertTrue(
+                distributionSha256.matches("[0-9a-f]{64}"),
+                "distributionSha256Sum must be 64 lowercase hexadecimal characters"
+        );
+        assertEquals(
+                REVIEWED_DISTRIBUTION_SHA256,
+                distributionSha256,
+                "The checksum must match the reviewed Maven 3.9.11 distribution"
+        );
+    }
+
+    /**
+     * Requires a fail-closed integrity preflight immediately before every CI/SBOM wrapper step.
+     *
+     * <p>The preflight must have the same GitHub Actions {@code if:} condition as the wrapper step,
+     * so neither Unix nor Windows execution can bootstrap Maven without validating the reviewed
+     * distribution URL and checksum first.</p>
+     *
+     * @throws IOException when a workflow cannot be read as repository source
+     */
+    @Test
+    void preflightsEveryCiAndSbomWrapperInvocation() throws IOException {
+        for (String workflow : List.of(
+                ".github/workflows/ci.yml",
+                ".github/workflows/sbom.yml"
+        )) {
+            List<String> lines = Files.readAllLines(
+                    projectRoot().resolve(workflow),
+                    StandardCharsets.UTF_8
+            );
+            int wrapperInvocations = 0;
+
+            for (int lineIndex = 0; lineIndex < lines.size(); lineIndex++) {
+                String line = lines.get(lineIndex).trim();
+                if (!line.startsWith("run:") || !containsWrapperInvocation(line)) {
+                    continue;
+                }
+                wrapperInvocations++;
+
+                int wrapperStep = previousStepStart(lines, lineIndex);
+                int preflightStep = previousStepStart(lines, wrapperStep - 1);
+                assertTrue(
+                        preflightStep >= 0,
+                        workflow + ": wrapper invocation must have a preceding preflight step"
+                );
+
+                String preflightBlock = String.join(
+                        "\n",
+                        lines.subList(preflightStep, wrapperStep)
+                );
+                assertTrue(
+                        preflightBlock.contains(PREFLIGHT_COMMAND),
+                        workflow + ": every Maven Wrapper invocation must be immediately preceded "
+                                + "by the integrity preflight"
+                );
+
+                String wrapperCondition = stepCondition(lines, wrapperStep, lineIndex + 1);
+                String preflightCondition = stepCondition(lines, preflightStep, wrapperStep);
+                assertEquals(
+                        wrapperCondition,
+                        preflightCondition,
+                        workflow + ": preflight and wrapper step must use the same condition"
+                );
+            }
+
+            assertTrue(
+                    wrapperInvocations > 0,
+                    workflow + ": expected at least one Maven Wrapper invocation"
+            );
+        }
+    }
+
+    private static boolean containsWrapperInvocation(String line) {
+        return line.contains("./mvnw ") || line.contains(".\\mvnw.cmd ");
+    }
+
+    private static int previousStepStart(List<String> lines, int fromIndex) {
+        for (int lineIndex = fromIndex; lineIndex >= 0; lineIndex--) {
+            if (lines.get(lineIndex).trim().startsWith("- name:")) {
+                return lineIndex;
+            }
+        }
+        return -1;
+    }
+
+    private static String stepCondition(List<String> lines, int startInclusive, int endExclusive) {
+        for (int lineIndex = startInclusive; lineIndex < endExclusive; lineIndex++) {
+            String line = lines.get(lineIndex).trim();
+            if (line.startsWith("if:")) {
+                return line;
+            }
+        }
+        return "";
+    }
+
+    /**
+     * Finds the repository root from reactor-root or module-local Maven execution.
+     *
+     * @return absolute repository root containing the wrapper configuration
+     */
+    private static Path projectRoot() {
+        Path current = Paths.get(System.getProperty("user.dir")).toAbsolutePath();
+        Path lastPomParent = null;
+        while (current != null) {
+            if (Files.exists(current.resolve(".git"))) {
+                return current;
+            }
+            if (Files.exists(current.resolve("pom.xml"))) {
+                lastPomParent = current;
+            }
+            current = current.getParent();
+        }
+        if (lastPomParent != null) {
+            return lastPomParent;
+        }
+        throw new IllegalStateException("Could not find project root");
+    }
+}