fix: keep native Antigravity hook for unusable Bash

.antigravity-plugin/hooks/ensure-monk-agent.ps1

@@ -12,9 +12,41 @@ $ErrorActionPreference = "SilentlyContinue"
 # Drain stdin so Antigravity's writer never blocks, even though we ignore it.
 [Console]::In.ReadToEnd() | Out-Null
 
-# If bash is available the .sh sibling handles this; bow out silently so the two
-# hooks never both emit JSON (Antigravity runs every hook in the list).
-if (Get-Command bash -ErrorAction SilentlyContinue) { exit 0 }
+# If a usable bash is available the .sh sibling handles this; bow out silently
+# so the two hooks never both emit JSON (Antigravity runs every hook in the
+# list). Command presence alone is insufficient: Windows can expose the legacy
+# WSL bash.exe launcher even when no distro contains /bin/bash, in which case
+# the POSIX sibling cannot run and this native hook still needs to handle the
+# invocation.
+$BashUsable = $false
+$BashCommand = Get-Command bash -ErrorAction SilentlyContinue
+if ($BashCommand -and $BashCommand.CommandType -eq "Application") {
+  $BashProbe = New-Object System.Diagnostics.Process
+  try {
+    $BashProbe.StartInfo.FileName = $BashCommand.Source
+    $BashProbe.StartInfo.Arguments = '-lc "exit 0"'
+    $BashProbe.StartInfo.UseShellExecute = $false
+    $BashProbe.StartInfo.RedirectStandardOutput = $true
+    $BashProbe.StartInfo.RedirectStandardError = $true
+    $BashProbe.StartInfo.CreateNoWindow = $true
+    if ($BashProbe.Start()) {
+      # Drain redirected streams asynchronously so a broken launcher cannot
+      # block while reporting its own startup failure.
+      $null = $BashProbe.StandardOutput.ReadToEndAsync()
+      $null = $BashProbe.StandardError.ReadToEndAsync()
+      if ($BashProbe.WaitForExit(2000)) {
+        $BashUsable = $BashProbe.ExitCode -eq 0
+      } else {
+        $BashProbe.Kill()
+      }
+    }
+  } catch {
+    $BashUsable = $false
+  } finally {
+    $BashProbe.Dispose()
+  }
+}
+if ($BashUsable) { exit 0 }
 
 $Port = if ($env:MONK_AGENT_PORT) { $env:MONK_AGENT_PORT } else { "7419" }
 $AgentHost = if ($env:MONK_AGENT_HOST) { $env:MONK_AGENT_HOST } else { "127.0.0.1" }

tests/antigravity-ensure-unusable-bash-stub.ps1

@@ -0,0 +1,105 @@
+$ErrorActionPreference = "Stop"
+
+$RepoRoot = Split-Path -Parent $PSScriptRoot
+$Hook = Join-Path $RepoRoot ".antigravity-plugin\hooks\ensure-monk-agent.ps1"
+$PowerShell = Join-Path $env:SystemRoot "System32\WindowsPowerShell\v1.0\powershell.exe"
+$TempRoot = Join-Path ([IO.Path]::GetTempPath()) ("monk-antigravity-bash-stub-" + [Guid]::NewGuid().ToString("N"))
+
+New-Item -ItemType Directory -Force -Path $TempRoot | Out-Null
+try {
+  # Model the legacy Windows/WSL bash.exe launcher when WSL is installed but
+  # no usable /bin/bash exists. Get-Command succeeds; execution does not.
+  $BashStub = Join-Path $TempRoot "bash.exe"
+  $BashSource = Join-Path $TempRoot "fake-bash.cs"
+  @"
+using System;
+using System.Threading;
+class Program {
+  static int Main() {
+    int delay;
+    if (int.TryParse(Environment.GetEnvironmentVariable("FAKE_BASH_DELAY_MS"), out delay) && delay > 0) {
+      Thread.Sleep(delay);
+    }
+    int exitCode;
+    return int.TryParse(Environment.GetEnvironmentVariable("FAKE_BASH_EXIT"), out exitCode) ? exitCode : 1;
+  }
+}
+"@ | Set-Content $BashSource
+
+  $Csc = Join-Path $env:WINDIR "Microsoft.NET\Framework64\v4.0.30319\csc.exe"
+  if (-not (Test-Path $Csc)) {
+    $Csc = Get-ChildItem "$env:WINDIR\Microsoft.NET\Framework64" -Filter csc.exe -Recurse |
+      Select-Object -First 1 -ExpandProperty FullName
+  }
+  if (-not $Csc) {
+    throw "csc.exe not found; cannot build the fake Bash launcher"
+  }
+  & $Csc /nologo /out:$BashStub $BashSource | Out-Null
+  if (-not (Test-Path $BashStub)) {
+    throw "failed to compile fake Bash launcher"
+  }
+
+  $OldPath = $env:PATH
+  $OldAgentPath = $env:MONK_AGENT_PATH
+  $OldPort = $env:MONK_AGENT_PORT
+  $OldBashExit = $env:FAKE_BASH_EXIT
+  $OldBashDelay = $env:FAKE_BASH_DELAY_MS
+  try {
+    $env:PATH = "$TempRoot;$env:SystemRoot\System32"
+    $env:MONK_AGENT_PATH = Join-Path $TempRoot "missing-monk-agent.exe"
+    $env:MONK_AGENT_PORT = "65534"
+    $env:FAKE_BASH_EXIT = "1"
+    $env:FAKE_BASH_DELAY_MS = "0"
+
+    $SelectedBash = Get-Command bash -ErrorAction Stop
+    if ($SelectedBash.Source -ne $BashStub) {
+      throw "fixture setup failed: expected $BashStub, got $($SelectedBash.Source)"
+    }
+
+    $Output = "{}" | & $PowerShell -NoProfile -ExecutionPolicy Bypass -File $Hook
+    if ($LASTEXITCODE -ne 0) {
+      throw "ensure hook exited with status $LASTEXITCODE"
+    }
+
+    $Text = [string]::Join("`n", @($Output))
+    if (-not $Text.Contains("monk-agent is not installed")) {
+      throw "FAIL: unusable bash command made the native Antigravity hook exit without its install guidance; stdout='$Text'"
+    }
+
+    # Preserve the intended de-duplication behavior when Bash is actually
+    # runnable: the native hook should yield to the concurrently registered
+    # POSIX sibling and emit nothing itself.
+    $env:FAKE_BASH_EXIT = "0"
+    $DelegatedOutput = "{}" | & $PowerShell -NoProfile -ExecutionPolicy Bypass -File $Hook
+    if ($LASTEXITCODE -ne 0) {
+      throw "ensure hook exited with status $LASTEXITCODE for a usable Bash command"
+    }
+    if (@($DelegatedOutput).Count -ne 0) {
+      throw "usable Bash command should suppress the native Antigravity hook; stdout='$DelegatedOutput'"
+    }
+
+    # A launcher that never returns must not consume the host's entire hook
+    # budget. The bounded probe should fall back to native guidance promptly.
+    $env:FAKE_BASH_DELAY_MS = "10000"
+    $Timer = [Diagnostics.Stopwatch]::StartNew()
+    $HungOutput = "{}" | & $PowerShell -NoProfile -ExecutionPolicy Bypass -File $Hook
+    $Timer.Stop()
+    $HungText = [string]::Join("`n", @($HungOutput))
+    if (-not $HungText.Contains("monk-agent is not installed")) {
+      throw "hung Bash command suppressed native install guidance; stdout='$HungText'"
+    }
+    if ($Timer.Elapsed.TotalSeconds -gt 6) {
+      throw "hung Bash liveness probe exceeded its bounded fallback time: $($Timer.Elapsed.TotalSeconds)s"
+    }
+  } finally {
+    $env:PATH = $OldPath
+    $env:MONK_AGENT_PATH = $OldAgentPath
+    $env:MONK_AGENT_PORT = $OldPort
+    $env:FAKE_BASH_EXIT = $OldBashExit
+    $env:FAKE_BASH_DELAY_MS = $OldBashDelay
+  }
+} finally {
+  Remove-Item -Recurse -Force $TempRoot -ErrorAction SilentlyContinue
+}
+
+Write-Output "PASS: unusable bash command does not suppress the native Antigravity ensure hook"