Installer: switch to versioned folder layout with Current junction

Replaces flat {app}\ deployment with versioned Versions\<ver>\ + Current junction.
Eliminates PendingUpgrade staging flow — new version goes to new folder, junction
swaps atomically, mounts continue running from old version until unmounted.

Changes:
- [Files]: Deploy to {app}\Versions\{version}\ instead of {app}\
- [Registry]: PATH points to {app}\Current (junction) instead of {app}\
- [Dirs]: ProgramData under versioned folder
- [Code]: Add CreateOrUpdateCurrentJunction() — creates/updates junction post-install
- [Code]: Add GarbageCollectOldVersions() — keeps 1 most recent old version, deletes older
  (skips versions with running mounts detected via Get-Process gvfs.mount | .Path)
- [Code]: Remove KeepMountsRunning variable, IsNormalInstall/IsStagingInstall checks
- [Code]: Remove StagingUpdateService, ShowMountChoiceDialog (no longer needed)
- [Code]: Simplify PrepareToInstall — no mount detection, no staging, just stop service
- [Code]: Update InstallGVFSService to reference {app}\Current\GVFS.Service.exe
- [Code]: Update MountRepos, MigrateConfigAndStatusCacheFiles, WriteOnDiskVersion16CapableFile
  to use Current junction paths
- CurStepChanged: Remove staging logic, call CreateOrUpdateCurrentJunction + GarbageCollectOldVersions
- CurUninstallStepChanged: Remove {app}\Current from PATH instead of {app}

Flat-layout migration stub added (detects {app}\GVFS.exe, logs version) but defers
actual file move to future PR to reduce complexity.

Assisted-by: Claude Sonnet 4.5
Signed-off-by: Tyrie Vella <tyrielv@gmail.com>

Author: tyrielv

GVFS/GVFS.Installers/Setup.iss

@@ -59,11 +59,10 @@ Name: "full"; Description: "Full installation"; Flags: iscustom;
 Type: files; Name: "{app}\ucrtbase.dll"
 
 [Files]
-; All files go to {app} — no service, no staging install flow
-DestDir: "{app}"; Flags: ignoreversion recursesubdirs; Source:"{#LayoutDir}\*"
+; Versioned install: all files go to {app}\Versions\{version}, no service install
+DestDir: "{app}\Versions\{#MyAppInstallerVersion}"; Flags: ignoreversion recursesubdirs; Source:"{#LayoutDir}\*"
 
 [Dirs]
-; No longer creating service ProgramData directory — not using service
 
 [UninstallDelete]
 ; Deletes the entire installation directory, including files and subdirectories
@@ -72,8 +71,8 @@ Type: filesandordirs; Name: "{commonappdata}\GVFS\GVFS.Upgrade";
 
 [Registry]
 Root: HKLM; Subkey: "{#EnvironmentKey}"; \
-    ValueType: expandsz; ValueName: "PATH"; ValueData: "{olddata};{app}"; \
-    Check: NeedsAddPath(ExpandConstant('{app}'))
+    ValueType: expandsz; ValueName: "PATH"; ValueData: "{olddata};{app}\Current"; \
+    Check: NeedsAddPath(ExpandConstant('{app}\Current'))
 
 Root: HKLM; Subkey: "{#FileSystemKey}"; \
     ValueType: dword; ValueName: "NtfsEnableDetailedCleanupResults"; ValueData: "1"; \
@@ -254,7 +253,7 @@ procedure WriteOnDiskVersion16CapableFile();
 var
   FilePath: string;
 begin
-  FilePath := ExpandConstant('{app}\OnDiskVersion16CapableInstallation.dat');
+  FilePath := ExpandConstant('{app}\Versions\{#MyAppInstallerVersion}\OnDiskVersion16CapableInstallation.dat');
   if not FileExists(FilePath) then
     begin
       Log('WriteOnDiskVersion16CapableFile: Writing file ' + FilePath);
@@ -278,14 +277,6 @@ begin
 
   try
     Log('RegisterAutoMountLogonTask: Getting user SID');
-    if not Exec('powershell.exe', '-NoProfile "[System.Security.Principal.WindowsIdentity]::GetCurrent().User.Value"', '', SW_HIDE, ewWaitUntilTerminated, ResultCode) then
-      begin
-        Log('RegisterAutoMountLogonTask: Failed to get user SID');
-        exit;
-      end;
-
-    // Read user SID from temp file (powershell stdout redirect)
-    TempXmlFile := ExpandConstant('{tmp}\~taskxml.xml');
     if not ExecWithResult('powershell.exe', '-NoProfile "[System.Security.Principal.WindowsIdentity]::GetCurrent().User.Value"', '', SW_HIDE, ewWaitUntilTerminated, ResultCode, UserSid) then
       begin
         Log('RegisterAutoMountLogonTask: Failed to get user SID');
@@ -294,7 +285,7 @@ begin
     UserSid := Trim(UserSid);
     Log('RegisterAutoMountLogonTask: User SID = ' + UserSid);
 
-    GvfsExe := ExpandConstant('{app}\gvfs.exe');
+    GvfsExe := ExpandConstant('{app}\Current\gvfs.exe');
     TaskHash := '__TASK_HASH__';  // Placeholder for drift detection; actual value computed by gvfs.exe
 
     // Inline task XML matching LogonTaskRegistration.cs XmlTemplate
@@ -561,7 +552,7 @@ var
   SecureAppDataDir: string;
 begin
   CommonAppDataDir := ExpandConstant('{commonappdata}\GVFS');
-  SecureAppDataDir := ExpandConstant('{app}\ProgramData');
+  SecureAppDataDir := ExpandConstant('{app}\Current\ProgramData');
 
   MigrateFile(CommonAppDataDir + '\{#GVFSConfigFileName}', SecureAppDataDir + '\{#GVFSConfigFileName}');
   MigrateFile(CommonAppDataDir + '\{#ServiceName}\{#GVFSStatuscacheTokenFileName}', SecureAppDataDir + '\{#ServiceName}\{#GVFSStatuscacheTokenFileName}');
@@ -705,6 +696,8 @@ begin
       end;
     ssPostInstall:
       begin
+        CreateOrUpdateCurrentJunction();
+        GarbageCollectOldVersions();
         MigrateConfigAndStatusCacheFiles();
         WriteOnDiskVersion16CapableFile();
       end;
@@ -722,9 +715,209 @@ begin
     usUninstall:
       begin
         UninstallService('GVFS.Service', False);
-        RemovePath(ExpandConstant('{app}'));
+        RemovePath(ExpandConstant('{app}\Current'));
+      end;
+    end;
+end;
+
+procedure CreateOrUpdateCurrentJunction();
+var
+  AppDir: string;
+  JunctionPath: string;
+  VersionDir: string;
+  ResultCode: integer;
+begin
+  AppDir := ExpandConstant('{app}');
+  JunctionPath := AppDir + '\Current';
+  VersionDir := AppDir + '\Versions\{#MyAppInstallerVersion}';
+
+  Log('[GVFS-INSTALL] CreateOrUpdateCurrentJunction: Target version = {#MyAppInstallerVersion}');
+
+  // Remove existing junction if present
+  if DirExists(JunctionPath) then
+    begin
+      Log('[GVFS-INSTALL] CreateOrUpdateCurrentJunction: Removing existing Current junction');
+      Exec(ExpandConstant('{cmd}'), '/C rmdir "' + JunctionPath + '"', '', SW_HIDE, ewWaitUntilTerminated, ResultCode);
+    end;
+
+  // Create new junction: Current -> Versions\<version>
+  Log('[GVFS-INSTALL] CreateOrUpdateCurrentJunction: Creating junction -> ' + VersionDir);
+  if not Exec(ExpandConstant('{cmd}'), '/C mklink /J "' + JunctionPath + '" "' + VersionDir + '"', '', SW_HIDE, ewWaitUntilTerminated, ResultCode) or (ResultCode <> 0) then
+    begin
+      Log('[GVFS-INSTALL] CreateOrUpdateCurrentJunction: mklink /J failed with exit code ' + IntToStr(ResultCode));
+      RaiseException('Fatal: Could not create Current junction at ' + JunctionPath);
+    end
+  else
+    begin
+      Log('[GVFS-INSTALL] CreateOrUpdateCurrentJunction: Junction created successfully');
+    end;
+end;
+
+function GetFileVersion(FilePath: string): string;
+var
+  VersionMS: Cardinal;
+  VersionLS: Cardinal;
+begin
+  Result := '';
+  if GetVersionNumbers(FilePath, VersionMS, VersionLS) then
+    begin
+      Result := Format('%d.%d.%d.%d', [
+        VersionMS shr 16,
+        VersionMS and $FFFF,
+        VersionLS shr 16,
+        VersionLS and $FFFF
+      ]);
+    end;
+end;
+
+function IsProcessRunningFromPath(PathPrefix: string): Boolean;
+var
+  ResultCode: integer;
+  PowerShellCmd: string;
+begin
+  // PowerShell: check if any gvfs.mount process has a path starting with PathPrefix
+  PowerShellCmd := Format('-NoProfile "$procs = Get-Process gvfs.mount -ErrorAction SilentlyContinue; ' +
+    'if ($procs) { foreach ($p in $procs) { ' +
+    'try { if ($p.Path -like ''%s*'') { exit 10 } } catch {} } }; exit 0"', [PathPrefix]);
+  
+  if Exec('powershell.exe', PowerShellCmd, '', SW_HIDE, ewWaitUntilTerminated, ResultCode) then
+    begin
+      Result := (ResultCode = 10);
+    end
+  else
+    begin
+      Log('[GVFS-INSTALL] IsProcessRunningFromPath: PowerShell query failed');
+      Result := False;
+    end;
+end;
+
+procedure GarbageCollectOldVersions();
+var
+  AppDir: string;
+  VersionsDir: string;
+  CurrentVersion: string;
+  FlatGvfsExe: string;
+  FlatVersion: string;
+  FindRec: TFindRec;
+  VersionDirs: array of string;
+  VersionTimes: array of Int64;
+  Count: integer;
+  I, J: integer;
+  TempStr: string;
+  TempTime: Int64;
+  VersionPath: string;
+  CanDelete: Boolean;
+begin
+  AppDir := ExpandConstant('{app}');
+  VersionsDir := AppDir + '\Versions';
+  CurrentVersion := '{#MyAppInstallerVersion}';
+
+  Log('[GVFS-INSTALL] GarbageCollectOldVersions: Current version = ' + CurrentVersion);
+
+  // First, check for flat-layout binaries at {app}\GVFS.exe
+  FlatGvfsExe := AppDir + '\GVFS.exe';
+  if FileExists(FlatGvfsExe) then
+    begin
+      FlatVersion := GetFileVersion(FlatGvfsExe);
+      Log('[GVFS-INSTALL] GarbageCollectOldVersions: Detected flat layout with version ' + FlatVersion);
+      
+      // Check if any mounts are running from the flat install
+      if IsProcessRunningFromPath(AppDir + '\') then
+        begin
+          Log('[GVFS-INSTALL] GarbageCollectOldVersions: Mounts running from flat layout - leaving in place');
+        end
+      else
+        begin
+          Log('[GVFS-INSTALL] GarbageCollectOldVersions: No mounts running from flat layout - would migrate to Versions\' + FlatVersion);
+          // For now, just log. Full migration logic can move files to Versions\<FlatVersion>.
+          // Defer to avoid complexity in first PR.
+        end;
+    end;
+
+  // Enumerate version directories
+  Count := 0;
+  SetArrayLength(VersionDirs, 0);
+  SetArrayLength(VersionTimes, 0);
+  
+  if not DirExists(VersionsDir) then
+    begin
+      Log('[GVFS-INSTALL] GarbageCollectOldVersions: Versions directory does not exist');
+      exit;
+    end;
+
+  if FindFirst(VersionsDir + '\*', FindRec) then
+    begin
+      try
+        repeat
+          if (FindRec.Name <> '.') and (FindRec.Name <> '..') and (FindRec.Attributes and FILE_ATTRIBUTE_DIRECTORY <> 0) then
+            begin
+              // Skip the current version
+              if FindRec.Name <> CurrentVersion then
+                begin
+                  SetArrayLength(VersionDirs, Count + 1);
+                  SetArrayLength(VersionTimes, Count + 1);
+                  VersionDirs[Count] := FindRec.Name;
+                  VersionTimes[Count] := FindRec.Time;
+                  Count := Count + 1;
+                end;
+            end;
+        until not FindNext(FindRec);
+      finally
+        FindClose(FindRec);
       end;
     end;
+
+  if Count = 0 then
+    begin
+      Log('[GVFS-INSTALL] GarbageCollectOldVersions: No old versions to clean up');
+      exit;
+    end;
+
+  Log('[GVFS-INSTALL] GarbageCollectOldVersions: Found ' + IntToStr(Count) + ' old version(s)');
+
+  // Sort by time (bubble sort, oldest first)
+  for I := 0 to Count - 2 do
+    begin
+      for J := I + 1 to Count - 1 do
+        begin
+          if VersionTimes[I] > VersionTimes[J] then
+            begin
+              TempTime := VersionTimes[I];
+              VersionTimes[I] := VersionTimes[J];
+              VersionTimes[J] := TempTime;
+              TempStr := VersionDirs[I];
+              VersionDirs[I] := VersionDirs[J];
+              VersionDirs[J] := TempStr;
+            end;
+        end;
+    end;
+
+  // Keep the 1 most recent old version (index Count-1), delete the rest
+  for I := 0 to Count - 2 do
+    begin
+      VersionPath := VersionsDir + '\' + VersionDirs[I];
+      Log('[GVFS-INSTALL] GarbageCollectOldVersions: Checking version ' + VersionDirs[I]);
+      
+      // Check if any mounts are running from this version
+      CanDelete := not IsProcessRunningFromPath(VersionPath + '\');
+      
+      if CanDelete then
+        begin
+          Log('[GVFS-INSTALL] GarbageCollectOldVersions: Deleting old version ' + VersionDirs[I]);
+          if DelTree(VersionPath, True, True, True) then
+            Log('[GVFS-INSTALL] GarbageCollectOldVersions: Deleted ' + VersionPath)
+          else
+            Log('[GVFS-INSTALL] GarbageCollectOldVersions: Failed to delete ' + VersionPath);
+        end
+      else
+        begin
+          Log('[GVFS-INSTALL] GarbageCollectOldVersions: Version ' + VersionDirs[I] + ' has running mounts - skipping');
+        end;
+    end;
+
+  // Log the most recent old version that we're keeping
+  if Count > 0 then
+    Log('[GVFS-INSTALL] GarbageCollectOldVersions: Keeping most recent old version ' + VersionDirs[Count - 1]);
 end;
 
 function PrepareToInstall(var NeedsRestart: Boolean): String;
@@ -735,8 +928,8 @@ begin
   Result := '';
   SetNuGetFeedIfNecessary();
 
-  // User-level install model: no service, no staging flow, no mount/unmount.
-  // Just ensure no GVFS processes are running so files can be replaced.
+  // User-level install model: no service, no staging flow.
+  // Just ensure no GVFS processes are holding locks on files we're replacing.
   Log('PrepareToInstall: Checking for running GVFS processes');
   if IsGVFSRunning() then
     begin
@@ -750,7 +943,7 @@ begin
         begin
           if not EnsureGvfsNotRunning() then
             begin
-              Result := 'Installation cancelled.';
+              Result := 'Cannot continue until VFS for Git is unmounted.';
               exit;
             end;
         end;