Eliminate conhost.exe from git.exe and hooks process launches

GVFS launches git.exe processes with CreateNoWindow=true (or
CREATE_NO_WINDOW in native code). Despite the name, this flag tells
Windows to create a new hidden console for each child process, which
allocates a conhost.exe instance. For frequent, small git operations
(e.g., during prefetch), the per-process conhost creation/teardown
overhead is disproportionately large.

Changes:

- GitProcess.cs: Set CreateNoWindow=false. With UseShellExecute=false
  and stdout/stderr redirected to pipes, the child inherits the
  parent's console state. Since GVFS.Mount runs as a service with no
  console, the child gets no console and no conhost. Also remove the
  unused redirectStandardError parameter (all callers pass true).

- ProcessHelper.cs: Set CreateNoWindow=false unconditionally. When
  redirectOutput is true, I/O goes through pipes so no console is
  needed. When redirectOutput is false, the child inherits the
  parent's console handles, which is correct for terminal contexts
  and harmless in service contexts (output was already going to an
  invisible hidden console).

- GitHooksLoader.cpp: Use DETACHED_PROCESS instead of
  CREATE_NO_WINDOW in the no-console branch. Explicitly detaches
  from any console without allocating a new one. The console branch
  (user terminal) is unchanged.

Verified with edge-case tests across terminal, hidden-console, and
fully-detached (DETACHED_PROCESS) parent contexts. All git status,
git fetch (prefetch hook), and gvfs health scenarios pass.

Assisted-by: Tyrie Vella <tyrielv@gmail.com>
Assisted-by: Claude Opus 4.6
Signed-off-by: Tyrie Vella <tyrielv@gmail.com>

Author: Nathan Baird

GVFS/GVFS.Common/Git/GitProcess.cs

@@ -815,16 +815,24 @@ public Result MultiPackIndexRepack(string gitObjectDirectory, string batchSize)
             return this.InvokeGitAgainstDotGitFolder($"-c pack.threads=1 -c repack.packKeptObjects=true multi-pack-index repack --object-dir=\"{gitObjectDirectory}\" --batch-size={batchSize} --no-progress");
         }
 
-        public Process GetGitProcess(string command, string workingDirectory, string dotGitDirectory, bool useReadObjectHook, bool redirectStandardError, string gitObjectsDirectory, bool usePreCommandHook)
+        public Process GetGitProcess(string command, string workingDirectory, string dotGitDirectory, bool useReadObjectHook, string gitObjectsDirectory, bool usePreCommandHook)
         {
             ProcessStartInfo processInfo = new ProcessStartInfo(this.gitBinPath);
             processInfo.WorkingDirectory = workingDirectory;
             processInfo.UseShellExecute = false;
             processInfo.RedirectStandardInput = true;
             processInfo.RedirectStandardOutput = true;
-            processInfo.RedirectStandardError = redirectStandardError;
+            processInfo.RedirectStandardError = true;
             processInfo.WindowStyle = ProcessWindowStyle.Hidden;
-            processInfo.CreateNoWindow = true;
+
+            // CreateNoWindow=false avoids allocating a hidden conhost.exe per child
+            // process. This is safe because both stdout and stderr are redirected via
+            // pipes, so the child never needs a console for I/O. If a future change
+            // stops redirecting either stream (to forward output to the parent console
+            // instead), CreateNoWindow must be set to true for that case — otherwise
+            // the non-redirected stream inherits the parent's console handle, which
+            // may be absent when running as a service, causing lost output.
+            processInfo.CreateNoWindow = false;
 
             processInfo.StandardOutputEncoding = UTF8NoBOM;
             processInfo.StandardErrorEncoding = UTF8NoBOM;
@@ -903,7 +911,7 @@ protected virtual Result InvokeGitImpl(
                 // From https://msdn.microsoft.com/en-us/library/system.diagnostics.process.standardoutput.aspx
                 // To avoid deadlocks, use asynchronous read operations on at least one of the streams.
                 // Do not perform a synchronous read to the end of both redirected streams.
-                using (this.executingProcess = this.GetGitProcess(command, workingDirectory, dotGitDirectory, useReadObjectHook, redirectStandardError: true, gitObjectsDirectory: gitObjectsDirectory, usePreCommandHook: usePreCommandHook))
+                using (this.executingProcess = this.GetGitProcess(command, workingDirectory, dotGitDirectory, useReadObjectHook, gitObjectsDirectory: gitObjectsDirectory, usePreCommandHook: usePreCommandHook))
                 {
                     StringBuilder output = new StringBuilder();
                     StringBuilder errors = new StringBuilder();

GVFS/GVFS.Common/ProcessHelper.cs

@@ -18,7 +18,16 @@ public static ProcessResult Run(string programName, string args, bool redirectOu
             processInfo.RedirectStandardOutput = redirectOutput;
             processInfo.RedirectStandardError = redirectOutput;
             processInfo.WindowStyle = ProcessWindowStyle.Hidden;
-            processInfo.CreateNoWindow = redirectOutput;
+
+            // CreateNoWindow=false avoids allocating a hidden conhost.exe per child
+            // process. When redirectOutput is true, I/O goes through pipes so no
+            // console is needed. When redirectOutput is false, the child inherits the
+            // parent's console handles — this works when the parent has a console
+            // (e.g., GVFS.Hooks invoked from a terminal), but output is silently lost
+            // when the parent has no console (e.g., service context). This is
+            // acceptable because CreateNoWindow=true would only send that output to
+            // an invisible hidden console instead.
+            processInfo.CreateNoWindow = false;
             processInfo.Arguments = args;
 
             return Run(processInfo);

GVFS/GitHooksLoader/GitHooksLoader.cpp

@@ -129,7 +129,7 @@ int ExecuteHook(const std::wstring &applicationName, wchar_t *hookName, int argc
         /* Git disallows stdin from hooks */
         si.dwFlags = STARTF_USESTDHANDLES;
 
-        creationFlags |= CREATE_NO_WINDOW;
+        creationFlags |= DETACHED_PROCESS;
     }
 
     ZeroMemory(&pi, sizeof(pi));