diff --git a/apps/multiplatform/common/src/desktopMain/kotlin/chat/simplex/common/views/helpers/AppUpdater.kt b/apps/multiplatform/common/src/desktopMain/kotlin/chat/simplex/common/views/helpers/AppUpdater.kt
index c4c34a1db9..783c438f66 100644
--- a/apps/multiplatform/common/src/desktopMain/kotlin/chat/simplex/common/views/helpers/AppUpdater.kt
+++ b/apps/multiplatform/common/src/desktopMain/kotlin/chat/simplex/common/views/helpers/AppUpdater.kt
@@ -29,6 +29,7 @@ import java.net.Proxy
 import java.nio.file.Files
 import java.nio.file.StandardCopyOption
 import kotlin.math.min
+import kotlin.system.exitProcess
 
 data class SemVer(
   val major: Int,
@@ -315,6 +316,10 @@ private suspend fun downloadAsset(asset: GitHubAsset) {
     call.execute().use { response ->
       response.body?.use { body ->
         body.byteStream().use { stream ->
+          // On Windows the install path exits the app before it can delete the downloaded file, so a
+          // previous update's installer can be left in the temp dir; remove it here at the next
+          // download instead of letting it accumulate. Other platforms delete the file after install.
+          if (desktopPlatform.isWindows()) File(tmpDir, asset.name).delete()
           createTmpFileAndDelete { file ->
             // It's important to close output stream (with use{}), otherwise, Windows cannot rename the file
             file.outputStream().use { output ->
@@ -433,19 +438,12 @@ private suspend fun installAppUpdate(file: File) = withContext(Dispatchers.IO) {
       }
     }
     desktopPlatform.isWindows() -> {
-      val process = Runtime.getRuntime().exec("msiexec /i ${file.absolutePath}"/* /qb */).onExit().join()
-      val startedInstallation = process.exitValue() == 0
-      if (!startedInstallation) {
-        Log.e(TAG, "Error starting installation: ${process.inputReader().use { it.readLines().joinToString("\n") }}${process.errorStream.use { String(it.readAllBytes()) }}")
-        // Failed to start installation. show directory with the file for manual installation
-        desktopOpenDir(file.parentFile)
-      } else {
-        AlertManager.shared.showAlertMsg(
-          title = generalGetString(MR.strings.app_check_for_updates_installed_successfully_title),
-          text = generalGetString(MR.strings.app_check_for_updates_installed_successfully_desc)
-        )
-        file.delete()
-      }
+      // Launch the installer, then exit so our files are no longer locked. While the app runs it
+      // holds SimpleX.exe/JRE/DLLs open, which forces the MSI to defer replacement to a reboot and
+      // corrupts the upgrade (the app then fails to launch). Array form passes the path as a single
+      // argument so a space in the temp path does not break the command.
+      Runtime.getRuntime().exec(arrayOf("msiexec", "/i", file.absolutePath))
+      exitProcess(0)
     }
     desktopPlatform.isMac() -> {
       // Default mount point if no other DMGs were mounted before
diff --git a/plans/2026-06-23-fix-windows-msi-update-running-app.md b/plans/2026-06-23-fix-windows-msi-update-running-app.md
new file mode 100644
index 0000000000..d276dbfe6f
--- /dev/null
+++ b/plans/2026-06-23-fix-windows-msi-update-running-app.md
@@ -0,0 +1,83 @@
+# Fix: Windows desktop fails to launch after in-app MSI update
+
+Issue: https://github.com/simplex-chat/simplex-chat/issues/7105
+
+## Symptom
+
+After updating SimpleX Desktop on Windows via the in-app updater (MSI), the MSI reports
+success but `SimpleX.exe` never launches afterwards — no window, no process in Task Manager,
+and it persists across a reboot. No application crash is logged. Reported on Windows 11
+(6.5.4 → 7.0.0), and the reporter saw it on a prior update too.
+
+Event Viewer shows the cause: RestartManager 10010 (`SimpleX.exe … cannot be restarted -
+Application SID does not match Conductor SID`) followed by MsiInstaller 1038
+(`requires a system restart … Reason for Restart: 1` = files in use).
+
+## Root cause
+
+The Windows branch of `installAppUpdate` (`AppUpdater.kt`) ran the MSI **while the app was
+still running** and waited for it (`Runtime.getRuntime().exec("msiexec /i …").onExit().join()`).
+The desktop MSI is a per-machine major upgrade (`desktop/build.gradle.kts`:
+`perUserInstall = false`, fixed `upgradeUuid`), so it must replace `SimpleX.exe`, the bundled
+JRE and the app DLLs in `C:\Program Files\SimpleX`. The running JVM holds those files open, so
+the installer cannot replace them: Restart Manager can't close the app across the
+user/elevated security boundary (the "SID does not match" event), the locked files are
+deferred to `PendingFileRenameOperations`, and a reboot is requested. At reboot the deferred
+uninstall-then-install operations leave the install directory inconsistent, so the executable
+never starts.
+
+macOS and Linux are unaffected because those kernels allow a running executable's file to be
+replaced by inode; Windows locks open files, so the app must release its locks before the MSI
+replaces them.
+
+## Fix
+
+Launch the installer and **exit the app immediately** instead of waiting, so the files are
+unlocked before the MSI reaches its file-replacement phase (which happens only after UAC
+elevation and the installer's costing phase — well after the JVM is gone). With no running
+instance there are no locked files, no reboot deferral and no Restart Manager conflict.
+
+Two small changes, both confined to the Windows path:
+
+1. `installAppUpdate` Windows branch: replace the `msiexec … .onExit().join()` + result
+   handling with `Runtime.getRuntime().exec(arrayOf("msiexec", "/i", file.absolutePath))`
+   followed by `exitProcess(0)`. The array form also fixes a latent bug where a space in the
+   path broke the single-string `exec`.
+2. `downloadAsset`: before downloading, `if (desktopPlatform.isWindows()) File(tmpDir,
+   asset.name).delete()`. Because the app now exits before it can delete the installer, a
+   leftover MSI is removed at the next download instead of accumulating in the temp dir.
+
+The user reopens the updated app from the Start Menu (the MSI recreates the shortcut) — the
+same hand-off the updater already uses for the `.deb` path and all failure branches.
+
+## Alternatives considered
+
+- **Helper script that waits for exit, installs, then relaunches** — adds a generated batch
+  with PID-polling, relaunch and self-delete; its only benefit over exiting is auto-relaunch,
+  which is not worth the complexity and platform-specific fragility.
+- **Register the app with Restart Manager** so the elevated MSI can close/restart it —
+  jpackage apps don't register RM, the SID mismatch shows RM can't manage the process across
+  the elevation boundary anyway, and it is far more code.
+- **Keep the app running with `REBOOT=ReallySuppress` / repair flags** — does not address the
+  lock; in-use files still defer to a reboot.
+
+## Scope / out of scope
+
+- In scope: the Windows branch of `installAppUpdate` and a Windows-guarded cleanup in
+  `downloadAsset`. macOS, Linux AppImage and `.deb` paths are unchanged.
+- Trade-off accepted: the app no longer shows its own "installed successfully" dialog (it has
+  exited); msiexec shows its own progress UI and the relaunched app is the success signal.
+- Out of scope (separate follow-ups): the macOS install branch ignores `renameTo` results;
+  download failures are only logged with no user-facing error; no signature/SHA verification
+  of the downloaded artifact.
+
+## Test plan (Windows VM)
+
+1. Install a per-machine MSI built at a version below the latest release.
+2. Settings → Check for updates → download + Install the newer MSI.
+3. Before the fix: RestartManager 10010 + MsiInstaller 1038 (Reason 1) appear and the app
+   fails to launch after reboot (reproduces #7105).
+4. After the fix: the app exits, the MSI installs with no reboot request, and the new version
+   launches normally from the Start Menu; `C:\Program Files\SimpleX` is a complete install
+   with no queued `PendingFileRenameOperations`.
+5. Re-run with a user profile path containing a space to confirm the array-form `exec` fix.