fix(powershell): display search stderr (#3146)

This shows stderr output from `atuin search -i` in PowerShell:

The output looks like this:
<img width="628" height="149" alt="image"
src="https://github.com/user-attachments/assets/c0a4bc9a-5d57-415f-a5b4-9c497744c6e0"
/>


Currently reproducible with the following config:
```toml
[keymap.emacs]
"foo" = "bar"
"=" = "bar"
```

I started by using `Start-Process` in the first commit, but then rewrote
it entirely as using a `Process` object directly should be more stable
(`Start-Process` already [caused
issues](https://github.com/atuinsh/atuin/pull/2543#issuecomment-2647555114)
in the past).

This fixes the PowerShell part of #3134

## Checks
- [x] I am happy for maintainers to push small adjustments to this PR,
to speed up the review cycle
- [x] I have checked that there are no existing pull requests for the
same thing

1 files changed, 30 insertions, 8 deletions

diff --git a/crates/atuin/src/shell/atuin.ps1 b/crates/atuin/src/shell/atuin.ps1
index 33c2ba5f..7f6ad8cf 100644
--- a/crates/atuin/src/shell/atuin.ps1
+++ b/crates/atuin/src/shell/atuin.ps1
@@ -135,16 +135,40 @@ New-Module -Name Atuin -ScriptBlock {
 
         $previousOutputEncoding = [System.Console]::OutputEncoding
         $resultFile = New-TemporaryFile
+        $suggestion = ""
+        $errorOutput = ""
 
         try {
             [System.Console]::OutputEncoding = [System.Text.Encoding]::UTF8
 
-            # Atuin is started through Start-Process to avoid interfering with the current shell.
-            $env:ATUIN_SHELL = "powershell"
-            $env:ATUIN_QUERY = Get-CommandLine
-            $argString = "search -i --result-file ""$resultFile"" $ExtraArgs"
-            Start-Process -PassThru -NoNewWindow -FilePath atuin -ArgumentList $argString | Wait-Process
-            $suggestion = (Get-Content -Raw $resultFile -Encoding UTF8 | Out-String).Trim()
+            # Start-Process does some crazy stuff, just use the Process class directly to have more control.
+            $process = New-Object System.Diagnostics.Process
+            $process.StartInfo.FileName = "atuin"
+            $process.StartInfo.Arguments = "search -i --result-file ""$resultFile"" $ExtraArgs"
+            $process.StartInfo.UseShellExecute = $false
+            $process.StartInfo.RedirectStandardError = $true
+            $process.StartInfo.StandardErrorEncoding = [System.Text.Encoding]::UTF8
+            $process.StartInfo.EnvironmentVariables["ATUIN_SHELL"] = "powershell"
+            $process.StartInfo.EnvironmentVariables["ATUIN_QUERY"] = Get-CommandLine
+
+            try {
+                $process.Start() | Out-Null
+
+                # A single stream is redirected, so we can read it synchronously, but we have to start reading it
+                # before waiting for the process to exit, otherwise the buffer could fill up and cause a deadlock.
+                $errorOutput = $process.StandardError.ReadToEnd().Trim()
+                $process.WaitForExit()
+
+                $suggestion = (Get-Content -Raw $resultFile -Encoding UTF8 | Out-String).Trim()
+            }
+            catch {
+                $errorOutput = $_
+            }
+
+            if ($errorOutput) {
+                Write-Host -ForegroundColor Red "Atuin error:"
+                Write-Host -ForegroundColor DarkRed $errorOutput
+            }
 
             # If no shell prompt offset is set, initialize it from the current prompt line count.
             if ($null -eq $env:ATUIN_POWERSHELL_PROMPT_OFFSET) {
@@ -179,8 +203,6 @@ New-Module -Name Atuin -ScriptBlock {
         }
         finally {
             [System.Console]::OutputEncoding = $previousOutputEncoding
-            $env:ATUIN_SHELL = $null
-            $env:ATUIN_QUERY = $null
             Remove-Item $resultFile
         }
     }