Refactor Windows installer update process for improved file handling

- Introduced new macros `tryRenameProbe` and `waitForInstallDirWritable` to enhance the update process by ensuring files are accessible before replacement.
- Updated the `swapUpdateStaging` macro to include checks for file locks and implement a retry mechanism for directory removal, improving reliability during updates.
- Enhanced detail logging for better visibility during the update process.

packaging/windows/installer.nsh

@@ -121,8 +121,74 @@ Var FinalInstDir
   ${EndIf}
 !macroend
 
+; Returns 0 in $R9 when $R8 can be renamed (file unlocked / path free).
+; _ID must be unique per insert so labels do not collide.
+!macro tryRenameProbe _ID
+  StrCpy $R9 1
+  ${IfNot} ${FileExists} "$R8"
+    StrCpy $R9 0
+    Goto try_rename_probe_done_${_ID}
+  ${EndIf}
+
+  ClearErrors
+  Rename "$R8" "$R8.updating"
+  ${If} ${Errors}
+    Goto try_rename_probe_done_${_ID}
+  ${EndIf}
+
+  ; Leave the .updating name — the whole tree is about to be deleted.
+  StrCpy $R9 0
+  try_rename_probe_done_${_ID}:
+!macroend
+
+; Wait until the live install directory is released by the quitting app.
+!macro waitForInstallDirWritable
+  !insertmacro progressStatus "Waiting for Farm Control to release install files..."
+  DetailPrint "Waiting for install directory to become writable..."
+
+  StrCpy $R7 0
+  wait_install_writable:
+    ; Probe the main binaries — rename fails while the process still holds them.
+    StrCpy $R8 "$FinalInstDir\bin\FarmControl.exe"
+    !insertmacro tryRenameProbe farmcontrol
+    ${If} $R9 != 0
+      Goto wait_install_writable_retry
+    ${EndIf}
+
+    StrCpy $R8 "$FinalInstDir\bin\launcher.exe"
+    !insertmacro tryRenameProbe launcher
+    ${If} $R9 != 0
+      Goto wait_install_writable_retry
+    ${EndIf}
+
+    ; Also probe creating a temp file in the install root.
+    ClearErrors
+    FileOpen $R8 "$FinalInstDir\.farmcontrol-write-probe" w
+    ${If} $R8 == ""
+      Goto wait_install_writable_retry
+    ${EndIf}
+    FileClose $R8
+    Delete "$FinalInstDir\.farmcontrol-write-probe"
+    Goto wait_install_writable_done
+
+    wait_install_writable_retry:
+      IntOp $R7 $R7 + 1
+      ${If} $R7 < 60
+        Sleep 500
+        Goto wait_install_writable
+      ${EndIf}
+      !insertmacro progressFailure "Could not access the previous Farm Control installation."
+      Abort
+
+  wait_install_writable_done:
+!macroend
+
 !macro swapUpdateStaging
   !insertmacro progressPhase "Applying update"
+
+  ${If} ${FileExists} "$FinalInstDir"
+    !insertmacro waitForInstallDirWritable
+
     !insertmacro progressStatus "Replacing Farm Control with the new version..."
     DetailPrint "Replacing Farm Control with staged update..."
 
@@ -138,6 +204,10 @@ Var FinalInstDir
         !insertmacro progressFailure "Could not remove the previous Farm Control installation."
         Abort
       ${EndIf}
+  ${EndIf}
+
+  !insertmacro progressStatus "Activating new Farm Control installation..."
+  DetailPrint "Activating staged update..."
 
   ClearErrors
   Rename "$INSTDIR" "$FinalInstDir"