diff --git a/docs/netplan-v4-application.md b/docs/netplan-v4-application.md
index bf964b0..452f504 100644
--- a/docs/netplan-v4-application.md
+++ b/docs/netplan-v4-application.md
@@ -95,3 +95,37 @@ commissioning. Economic replay-based automatic family selection, full corrected
 feedback/control integration, long-term outbox/server retention and real live/
 failure acceptance remain open. Existing trial gates are unchanged. No sensor,
 accounting or hardware evidence identifier is fabricated by data ingestion.
+
+## Installer class-path correction (2026-10-03)
+
+The original commissioning installer loaded `source/libs/NetzfahrplanV4Messaufnahme.php`
+while importing observation history. A later Manager callback loads the installed
+copy at `modules/Enelix-EMS/libs/NetzfahrplanV4Messaufnahme.php`. PHP's once-only file
+inclusion does not deduplicate class declarations across those different files.
+The dependent `NetzfahrplanV4Bilanzierung` class is subject to the same collision.
+
+The tested installer-only fix is preserved in
+`examples/V4ApplicationData/application-class-loading.patch` (SHA256
+`6d53d74d4059bb1ae3a446350637a4f4a4a73cc2fd64d2fc2f0967bd23ec7173`).
+When building a commissioning package, load both classes only from the installed
+module tree, after validating their expected source hashes. Before any require,
+check both already-loaded origins without autoload. Reject a foreign staged origin
+with a controlled error; do not hide it by wrapping the class declaration in a guard.
+Include `installed_capture_bootstrap.php` in the package checksum map. Do not change
+the installed-module manifest or bless unrelated source changes.
+
+The Lihrenmoos staging entrypoint has this fix applied, with backups of its original
+installer and checksum map. No running modules, data files, timers, native callbacks,
+server components or actuator settings were changed by the repair. Actual completion
+still requires the user's fresh Symcon invocation of the corrected installer.
+
+Validation: the original two-path failure was reproduced with the real PHP classes.
+Thirteen additional isolated installer scenarios passed, including callback/reload
+loading order, preloaded dependencies, history import, repeat/finished import,
+foreign-class refusal, partial-import preservation, source drift, registration wait
+and first installation. These are PHP CLI tests with mocked IPS in temporary trees,
+not a completed test in the actual Symcon kernel.
+
+Evidence on the test host:
+`/srv/agent/netplan-v4-application-build/class-loading-fix/TEST_RESULTS.json` and
+`FIX_RESULT.json`. The test harness and exact candidate source are retained there.
diff --git a/examples/V4ApplicationData/application-class-loading.patch b/examples/V4ApplicationData/application-class-loading.patch
new file mode 100644
index 0000000..5b39d69
--- /dev/null
+++ b/examples/V4ApplicationData/application-class-loading.patch
@@ -0,0 +1,71 @@
+--- a/install.php
++++ b/install.php
+@@ -19,6 +19,8 @@
+     }
+     $before=json_decode(IPS_GetConfiguration($manager),true,128,JSON_THROW_ON_ERROR);
+     $report['files']=v4StageInstall(__DIR__,'/var/lib/symcon/modules/Enelix-EMS');
++    require_once __DIR__.'/installed_capture_bootstrap.php';
++    $report['classLoading']=v4ApplicationLoadInstalledCapture('/var/lib/symcon/modules/Enelix-EMS',__DIR__.'/MANIFEST.json');
+     $controls=[];
+     foreach (IPS_GetModuleList() as $mid) if ((IPS_GetModule($mid)['Prefix']??'')==='MC') $controls=array_merge($controls,IPS_GetInstanceListByModuleID($mid));
+     if (count($controls)!==1||!function_exists('MC_ReloadModule')) throw new RuntimeException('Module Control nicht eindeutig.');
+@@ -38,7 +40,7 @@
+         $marker=$dir.'/observer-import.json';
+         if (!is_file($marker)&&!IPS_GetProperty($manager,'NetzfahrplanV4MessdatenAktiv')) {
+             if (glob($dir.'/raw-*.jsonl')!==[]) throw new RuntimeException('Messdaten ohne Importabschluss vorhanden; nicht doppelt importieren.');
+-            require_once __DIR__.'/source/libs/NetzfahrplanV4Messaufnahme.php';
++            // Reuse the hash-checked installed class; never load the staged copy.
+             $count=0;$last=0;$cutoff=time()-172800;
+             $files=glob('/srv/agent/netplan-v4-separated-observer-stage/data/raw-*.jsonl');sort($files,SORT_STRING);
+             foreach ($files as $file) {
+--- /dev/null
++++ b/installed_capture_bootstrap.php
+@@ -0,0 +1,48 @@
++<?php
++
++declare(strict_types=1);
++
++/** Installer-only bootstrap. Load the same files the installed Manager uses.
++ * No IPS calls, source edits, state changes, or autoload of an unknown class.
++ */
++function v4ApplicationLoadInstalledCapture(string $target, string $manifestFile): array
++{
++    if (is_link($target) || realpath($target) !== $target || !is_dir($target)) {
++        throw new RuntimeException('Unerwartetes Modulverzeichnis.');
++    }
++    $manifest = json_decode((string) file_get_contents($manifestFile), true, 64, JSON_THROW_ON_ERROR);
++    if (($manifest['mode'] ?? null) !== 'data_application_only') {
++        throw new RuntimeException('Unerwarteter Installationsumfang.');
++    }
++    $classes = [
++        'Belevo\\EnelixEMS\\NetzfahrplanV4Bilanzierung' => 'libs/NetzfahrplanV4Bilanzierung.php',
++        'Belevo\\EnelixEMS\\NetzfahrplanV4Messaufnahme' => 'libs/NetzfahrplanV4Messaufnahme.php',
++    ];
++    // Check BOTH origins before loading either file, including the transitive dependency.
++    foreach ($classes as $class => $relative) {
++        $path = $target . '/' . $relative;
++        $expected = $manifest['files'][$relative]['after'] ?? null;
++        if (!is_string($expected) || !preg_match('/^[a-f0-9]{64}$/D', $expected)
++            || is_link($path) || !is_file($path) || realpath($path) !== $path
++            || hash_file('sha256', $path) !== $expected) {
++            throw new RuntimeException('Installierte Messbibliothek weicht vom geprueften Paket ab: ' . $relative);
++        }
++        if (class_exists($class, false)) {
++            $origin = (new ReflectionClass($class))->getFileName();
++            if ($origin !== $path) {
++                throw new RuntimeException('Messbibliothek bereits aus anderem Pfad geladen. Installationsaufruf separat ausfuehren, ohne weitere Sammler-Includes.');
++            }
++        }
++    }
++    foreach ($classes as $class => $relative) {
++        $path = $target . '/' . $relative;
++        if (!class_exists($class, false)) {
++            require_once $path;
++        }
++        if (!class_exists($class, false) || (new ReflectionClass($class))->getFileName() !== $path) {
++            throw new RuntimeException('Installierte Messbibliothek konnte nicht eindeutig geladen werden.');
++        }
++    }
++    return ['source' => 'installed_module_only', 'stagedClassesLoaded' => false,
++        'files' => array_values($classes)];
++}