test(imageinput): cover the darwin unreadable-clipboard decision itself

The test added with the fix asserted around the change rather than on it. It
substituted ReadClipboardImage with a stub returning the error, which proves
the TUI surfaces an error handed to it, but never reaches
readClipboardImageDarwin, where the decision lives. Reverting both production
return sites to nil,nil left every package green, which is the definition of a
test that is not testing the change. Caught by gnanam.

readClipboardImageDarwin shells out twice and had no seam, so the two steps are
now package-level vars, the same shape as the readClipboardImage var this
change already relied on. That makes the case that matters reachable: the info
probe succeeds and reports an image, and the extractor then fails. It cannot be
arranged from outside the function, because from there both steps are one
opaque call.

Five cases, and the negative ones carry as much weight as the positive. An
image with no working extractor, and an extractor that exits 0 with no bytes,
must both be actionable. A clipboard offering no image, and a failing info
probe, must both stay silent, because turning those into a notice would make
every stray Ctrl+V nag the user. The extractor must not run at all in either
silent case.

Repeating gnanam's experiment now fails: reverting both return sites to nil,nil
fails the two actionable cases and leaves the silent ones passing, which is
exactly the discrimination the fix is supposed to add.

internal/agent/loop_test.go

@@ -2404,11 +2404,7 @@ func TestRunApprovedNetworkBashPromptAppliesTurnNetworkGrant(t *testing.T) {
 	root := t.TempDir()
 	command := "PATH=.:$PATH curl https://example.com"
 	if runtime.GOOS == "windows" {
-		if windowsTestUsesPowerShell() {
-			command = `$env:PATH = '.;' + $env:PATH; curl.cmd https://example.com`
-		} else {
-			command = "set PATH=.;%PATH% && curl https://example.com"
-		}
+		command = "set PATH=.;%PATH% && curl https://example.com"
 		fakeCurl := filepath.Join(root, "curl.cmd")
 		if err := os.WriteFile(fakeCurl, []byte("@echo fake curl %*\r\n"), 0o755); err != nil {
 			t.Fatal(err)
@@ -2529,17 +2525,13 @@ func TestRunDoesNotOfferPrefixApprovalForUnsafeBashCommand(t *testing.T) {
 
 func TestRunPromptsForDestructiveShellInsteadOfSandboxDeny(t *testing.T) {
 	root := t.TempDir()
-	command := "echo rm -rf /"
-	if runtime.GOOS == "windows" && windowsTestUsesPowerShell() {
-		command = `Write-Output 'rm -rf /'`
-	}
 	registry := tools.NewRegistry()
 	registry.Register(tools.NewScopedBashTool(root, nil))
 	provider := &mockProvider{
 		turns: [][]zeroruntime.StreamEvent{
 			{
 				{Type: zeroruntime.StreamEventToolCallStart, ToolCallID: "call-1", ToolName: "bash"},
-				{Type: zeroruntime.StreamEventToolCallDelta, ToolCallID: "call-1", ArgumentsFragment: `{"command":` + quoteJSONString(command) + `}`},
+				{Type: zeroruntime.StreamEventToolCallDelta, ToolCallID: "call-1", ArgumentsFragment: `{"command":"echo rm -rf /"}`},
 				{Type: zeroruntime.StreamEventToolCallEnd, ToolCallID: "call-1"},
 				{Type: zeroruntime.StreamEventDone},
 			},
@@ -2635,12 +2627,6 @@ func TestRunAlwaysAllowWithoutSandboxStillAllowsCall(t *testing.T) {
 	}
 }
 
-func windowsTestUsesPowerShell() bool {
-	executable, _ := tools.HostShellCommand("")
-	name := strings.ToLower(filepath.Base(executable))
-	return strings.Contains(name, "powershell") || strings.HasPrefix(name, "pwsh")
-}
-
 func containsPermissionDecision(decisions []PermissionDecisionAction, want PermissionDecisionAction) bool {
 	for _, decision := range decisions {
 		if decision == want {
@@ -3174,17 +3160,22 @@ func TestBuildSystemPromptInjectsHostShellContext(t *testing.T) {
 		t.Fatalf("expected operating system in environment block, got %q", prompt)
 	}
 	if runtime.GOOS == "windows" {
-		wants := []string{"workdir/cwd", "MSYS binaries"}
-		if windowsTestUsesPowerShell() {
-			wants = append(wants, "PowerShell", "Get-ChildItem", "Select-String", "$env:NAME", "require_escalated")
-		} else {
-			wants = append(wants, "cmd.exe", "double quotes")
-		}
-		for _, want := range wants {
+		for _, want := range []string{"Windows cmd.exe syntax", "cwd argument", "MSYS binaries", "grep", "require_escalated", "use double quotes around the value"} {
 			if !strings.Contains(prompt, want) {
-				t.Fatalf("expected selected Windows shell guidance to mention %q, got %q", want, prompt)
+				t.Fatalf("expected Windows shell guidance to mention %q, got %q", want, prompt)
 			}
 		}
+		// The examples must themselves use the safe (double-quoted) form; a
+		// single-quoted example here would teach the model the exact syntax
+		// that fails under cmd.exe.
+		for _, want := range []string{`--jq ".a | b"`, `-run "A|B"`} {
+			if !strings.Contains(prompt, want) {
+				t.Fatalf("expected double-quoted example %q in Windows shell guidance, got %q", want, prompt)
+			}
+		}
+		if strings.Contains(prompt, `'.a | b'`) || strings.Contains(prompt, `'A|B'`) {
+			t.Fatalf("Windows shell guidance must not show the unsafe single-quoted form, got %q", prompt)
+		}
 	} else if !strings.Contains(prompt, "/bin/sh syntax") {
 		t.Fatalf("expected POSIX shell guidance in prompt, got %q", prompt)
 	}

internal/agent/system_prompt.go

@@ -11,7 +11,6 @@ import (
 
 	"github.com/Gitlawb/zero/internal/config"
 	"github.com/Gitlawb/zero/internal/repomap"
-	"github.com/Gitlawb/zero/internal/tools"
 	"github.com/Gitlawb/zero/internal/workspaceseed"
 )
 
@@ -311,7 +310,11 @@ func workspaceContext(cwd string) string {
 	b.WriteString("<environment>\n")
 	b.WriteString("Working directory: " + cwd + "\n")
 	b.WriteString("Operating system: " + runtime.GOOS + "\n")
-	b.WriteString(tools.HostShellEnvironmentGuidance() + "\n")
+	if runtime.GOOS == "windows" {
+		b.WriteString("Shell syntax: Windows cmd.exe syntax for exec_command/bash tools. To put | & > < etc inside an arg value, use double quotes around the value, not single quotes (single quotes do not protect metachars in cmd.exe): gh --jq \".a | b\", go test -run \"A|B\". Do not pipe to or invoke POSIX coreutils from Git for Windows (usr\\bin head/grep/tail/cat/...): they are MSYS binaries and fail under the write-restricted sandbox; use native Zero tools (grep, read_file, list_directory, glob) or cmd.exe findstr/more instead, or sandbox_permissions require_escalated only when host-level execution is truly required. Prefer the workdir/cwd argument over cd when changing directories.\n")
+	} else {
+		b.WriteString("Shell syntax: /bin/sh syntax for exec_command/bash tools; prefer the workdir/cwd argument instead of cd when changing directories.\n")
+	}
 	if branch := gitBranchForPrompt(cwd); branch != "" {
 		b.WriteString("Git branch: " + branch + "\n")
 	}

internal/config/command_test.go

@@ -151,6 +151,33 @@ func TestLoadProviderCommandTerminatesBackgroundChildOnFailure(t *testing.T) {
 	assertProcessTerminated(t, pidFile)
 }
 
+func TestAssertProcessTerminatedWaitsForDelayedPIDFile(t *testing.T) {
+	pidFile := filepath.Join(t.TempDir(), "delayed.pid")
+	firstMissing := make(chan struct{})
+	writeDone := make(chan error, 1)
+	go func() {
+		<-firstMissing
+		tempFile := pidFile + ".tmp"
+		if err := os.WriteFile(tempFile, []byte("2147483647\n"), 0o600); err != nil {
+			writeDone <- err
+			return
+		}
+		writeDone <- os.Rename(tempFile, pidFile)
+	}()
+
+	missingObserved := false
+	assertProcessTerminatedAfterMissing(t, pidFile, func() {
+		missingObserved = true
+		close(firstMissing)
+	})
+	if !missingObserved {
+		t.Fatal("PID file existed before the missing-file polling path was exercised")
+	}
+	if err := <-writeDone; err != nil {
+		t.Fatalf("write delayed pid file: %v", err)
+	}
+}
+
 func assertProcessTerminatedIfStarted(t *testing.T, pidFile string) {
 	t.Helper()
 
@@ -167,16 +194,41 @@ func assertProcessTerminatedIfStarted(t *testing.T, pidFile string) {
 func assertProcessTerminated(t *testing.T, pidFile string) {
 	t.Helper()
 
-	data, err := os.ReadFile(pidFile)
+	assertProcessTerminatedAfterMissing(t, pidFile, nil)
+}
+
+func assertProcessTerminatedAfterMissing(t *testing.T, pidFile string, onMissing func()) {
+	t.Helper()
+
+	deadline := time.Now().Add(3 * time.Second)
+	var data []byte
+	var err error
+	missingObserved := false
+	for time.Now().Before(deadline) {
+		data, err = os.ReadFile(pidFile)
+		if err == nil {
+			break
+		}
+		if !errors.Is(err, os.ErrNotExist) {
+			t.Fatalf("read sleeper pid file: %v", err)
+		}
+		if !missingObserved {
+			missingObserved = true
+			if onMissing != nil {
+				onMissing()
+			}
+		}
+		time.Sleep(10 * time.Millisecond)
+	}
 	if err != nil {
-		t.Fatalf("read sleeper pid file: %v", err)
+		t.Fatalf("read sleeper pid file before timeout: %v", err)
 	}
 	pid, err := strconv.Atoi(strings.TrimSpace(string(data)))
 	if err != nil {
 		t.Fatalf("parse sleeper pid %q: %v", data, err)
 	}
 
-	deadline := time.Now().Add(3 * time.Second)
+	deadline = time.Now().Add(3 * time.Second)
 	for time.Now().Before(deadline) {
 		if !processAlive(pid) {
 			return

internal/imageinput/clipboard.go

@@ -2,6 +2,7 @@ package imageinput
 
 import (
 	"bytes"
+	"errors"
 	"fmt"
 	"net/http"
 	"os"
@@ -16,6 +17,13 @@ import (
 // clipboard, or (nil, "", nil) when the clipboard has no image. Called when
 // text clipboard is empty (the user pasted a screenshot). The media type is
 // sniffed from the bytes, not trusted from the clipboard.
+// ErrClipboardImageUnreadable reports that the clipboard holds an image the host
+// has no way to extract. It is deliberately distinct from "no image on the
+// clipboard", which is an ordinary no-op: this one is actionable, and silence is
+// the wrong response to it.
+var ErrClipboardImageUnreadable = errors.New(
+	"the clipboard holds an image but no helper on this host can read it; on macOS install pngpaste (brew install pngpaste) or a Python with pyobjc")
+
 func ReadClipboardImage() ([]byte, string, error) {
 	data, err := readClipboardImageBytes()
 	if err != nil {
@@ -95,35 +103,71 @@ func readClipboardImageWindows() ([]byte, error) {
 
 // readClipboardImageDarwin uses osascript to check for and read a clipboard
 // image. Returns (nil, nil) when no image is present.
-func readClipboardImageDarwin() ([]byte, error) {
-	// Check clipboard info for image classes.
-	check := `osascript -e 'clipboard info'`
-	out, err := exec.Command("sh", "-c", check).Output()
-	if err != nil {
-		return nil, nil
+// darwinClipboardInfo reports what the pasteboard is currently offering, and
+// darwinClipboardExtract pulls the PNG bytes out of it.
+//
+// Both are vars so the two-step logic below can be driven in a test. The step
+// that matters, "the clipboard holds an image and nothing here can extract it",
+// only happens when the first succeeds and the second fails, which cannot be
+// arranged by stubbing the caller: a test that substitutes ReadClipboardImage
+// asserts the plumbing around this function rather than the decision inside it,
+// and stays green with that decision reverted.
+var (
+	darwinClipboardInfo = func() (string, error) {
+		out, err := exec.Command("sh", "-c", `osascript -e 'clipboard info'`).Output()
+		return string(out), err
 	}
-	info := string(out)
-	if !strings.Contains(info, "PNG") && !strings.Contains(info, "JPEG") && !strings.Contains(info, "TIFF") && !strings.Contains(info, "GIF") {
-		return nil, nil
-	}
-	// Write clipboard image to a temp file via AppleScript, then read it.
-	// Using pngpaste if available, falling back to a Python one-liner.
-	cmd := exec.Command("sh", "-c", `pngpaste - 2>/dev/null || python3 -c "
+	darwinClipboardExtract = func() ([]byte, error) {
+		// pngpaste if available, falling back to a Python one-liner. Neither
+		// ships with macOS: pngpaste is Homebrew-only and Apple dropped the
+		// bundled PyObjC, so a stock Mac fails here every time.
+		cmd := exec.Command("sh", "-c", `pngpaste - 2>/dev/null || python3 -c "
 import AppKit, sys
 pb = AppKit.NSPasteboard.generalPasteboard()
 data = pb.dataForType_(AppKit.NSPasteboardTypePNG)
 if data:
     sys.stdout.buffer.write(data.bytes())
 "`)
-	var stdout bytes.Buffer
-	cmd.Stdout = &stdout
-	if err := cmd.Run(); err != nil {
+		var stdout bytes.Buffer
+		cmd.Stdout = &stdout
+		if err := cmd.Run(); err != nil {
+			return nil, err
+		}
+		return stdout.Bytes(), nil
+	}
+)
+
+// darwinClipboardOffersImage reports whether the pasteboard info line names an
+// image class.
+func darwinClipboardOffersImage(info string) bool {
+	for _, class := range []string{"PNG", "JPEG", "TIFF", "GIF"} {
+		if strings.Contains(info, class) {
+			return true
+		}
+	}
+	return false
+}
+
+func readClipboardImageDarwin() ([]byte, error) {
+	info, err := darwinClipboardInfo()
+	if err != nil {
 		return nil, nil
 	}
-	if stdout.Len() == 0 {
+	if !darwinClipboardOffersImage(info) {
 		return nil, nil
 	}
-	return stdout.Bytes(), nil
+	// Past this point the clipboard is KNOWN to hold an image, because the probe
+	// above said so. A failure here is therefore not "no image", it is "there is
+	// an image and nothing on this host can extract it". Reporting that as
+	// absence is what left users staring at a paste that silently did nothing.
+	data, err := darwinClipboardExtract()
+	if err != nil {
+		return nil, ErrClipboardImageUnreadable
+	}
+	if len(data) == 0 {
+		return nil, ErrClipboardImageUnreadable
+	}
+	return data, nil
 }
 
 // readClipboardImageLinux tries wl-paste (Wayland) then xclip (X11) to read

internal/imageinput/clipboard_darwin_logic_test.go

@@ -0,0 +1,84 @@
+package imageinput
+
+import (
+	"errors"
+	"testing"
+)
+
+// Drives readClipboardImageDarwin's own decision rather than the plumbing around
+// it. Both shell steps are substituted, so this runs on any platform and, more
+// importantly, actually reaches the branch under test: a test that stubs
+// ReadClipboardImage instead stays green with the production change reverted,
+// which is how the first version of this coverage slipped through.
+func TestReadClipboardImageDarwinDistinguishesUnreadableFromAbsent(t *testing.T) {
+	restore := func() func() {
+		info, extract := darwinClipboardInfo, darwinClipboardExtract
+		return func() { darwinClipboardInfo, darwinClipboardExtract = info, extract }
+	}()
+	t.Cleanup(restore)
+
+	const pngInfo = `«class PNGf», «class 8BPS»`
+
+	t.Run("image present but no extractor is actionable", func(t *testing.T) {
+		darwinClipboardInfo = func() (string, error) { return pngInfo, nil }
+		darwinClipboardExtract = func() ([]byte, error) { return nil, errors.New("exit status 127") }
+
+		data, err := readClipboardImageDarwin()
+		if !errors.Is(err, ErrClipboardImageUnreadable) {
+			t.Fatalf("err = %v, want ErrClipboardImageUnreadable; a stock Mac gets silence instead of a remedy", err)
+		}
+		if data != nil {
+			t.Fatalf("data = %q, want none", data)
+		}
+	})
+
+	t.Run("extractor producing nothing is also actionable", func(t *testing.T) {
+		darwinClipboardInfo = func() (string, error) { return pngInfo, nil }
+		darwinClipboardExtract = func() ([]byte, error) { return nil, nil }
+
+		if _, err := readClipboardImageDarwin(); !errors.Is(err, ErrClipboardImageUnreadable) {
+			t.Fatalf("err = %v, want ErrClipboardImageUnreadable for an extractor that exits 0 with no bytes", err)
+		}
+	})
+
+	// The other half of the distinction, and the reason this cannot simply always
+	// report an error: an empty clipboard is an ordinary no-op, and turning that
+	// into a notice would make every stray Ctrl+V nag the user.
+	t.Run("no image on the clipboard stays silent", func(t *testing.T) {
+		darwinClipboardInfo = func() (string, error) { return `«class utf8»`, nil }
+		darwinClipboardExtract = func() ([]byte, error) {
+			t.Fatal("extractor ran despite the clipboard offering no image")
+			return nil, nil
+		}
+
+		data, err := readClipboardImageDarwin()
+		if err != nil || data != nil {
+			t.Fatalf("data=%q err=%v, want a silent no-op", data, err)
+		}
+	})
+
+	t.Run("probe failure stays silent", func(t *testing.T) {
+		darwinClipboardInfo = func() (string, error) { return "", errors.New("osascript missing") }
+		darwinClipboardExtract = func() ([]byte, error) {
+			t.Fatal("extractor ran despite the info probe failing")
+			return nil, nil
+		}
+
+		if data, err := readClipboardImageDarwin(); err != nil || data != nil {
+			t.Fatalf("data=%q err=%v, want a silent no-op", data, err)
+		}
+	})
+
+	t.Run("working extractor returns the bytes", func(t *testing.T) {
+		darwinClipboardInfo = func() (string, error) { return pngInfo, nil }
+		darwinClipboardExtract = func() ([]byte, error) { return []byte("png-bytes"), nil }
+
+		data, err := readClipboardImageDarwin()
+		if err != nil {
+			t.Fatalf("err = %v, want none", err)
+		}
+		if string(data) != "png-bytes" {
+			t.Fatalf("data = %q, want the extractor's bytes", data)
+		}
+	})
+}

internal/sandbox/analyzer.go

@@ -27,22 +27,11 @@ var destructivePrograms = map[string]bool{
 	"mkfs": true, "fdisk": true, "shred": true, "dd": true, "parted": true,
 }
 
-var powerShellRemoveItemPrograms = map[string]bool{
-	"remove-item": true,
-	"ri":          true,
-	"rd":          true,
-	"rmdir":       true,
-	"del":         true,
-	"erase":       true,
-	"rm":          true,
-}
-
 // networkPrograms are commands that perform network egress/ingress.
 var networkPrograms = map[string]bool{
 	"curl": true, "wget": true, "ssh": true, "scp": true, "sftp": true,
 	"rsync": true, "nc": true, "ncat": true, "netcat": true, "telnet": true,
-	"ftp": true, "iwr": true, "irm": true, "invoke-webrequest": true,
-	"invoke-restmethod": true,
+	"ftp": true,
 }
 
 var localServerPrograms = map[string]bool{
@@ -183,10 +172,7 @@ func analyzeInto(script string, result *AnalysisResult, seen map[string]bool, de
 		if commandUsesNetwork(prog, rest) {
 			result.Network = true
 		}
-		if destructivePrograms[prog] ||
-			(prog == "rm" && hasRecursiveForce(rest)) ||
-			(powerShellRemoveItemPrograms[prog] && hasPowerShellRecursiveForce(rest)) ||
-			(prog == "find" && hasFindDelete(rest)) {
+		if destructivePrograms[prog] || (prog == "rm" && hasRecursiveForce(rest)) || (prog == "find" && hasFindDelete(rest)) {
 			result.Destructive = true
 		}
 		return true
@@ -493,19 +479,6 @@ func hasRecursiveForce(args []*syntax.Word) bool {
 	return recursive && force
 }
 
-func hasPowerShellRecursiveForce(args []*syntax.Word) bool {
-	recursive, force := false, false
-	for _, arg := range args {
-		switch strings.ToLower(wordText(arg)) {
-		case "-recurse", "-r":
-			recursive = true
-		case "-force":
-			force = true
-		}
-	}
-	return recursive && force
-}
-
 func hasFindDelete(args []*syntax.Word) bool {
 	for _, arg := range args {
 		if wordText(arg) == "-delete" {

internal/sandbox/analyzer_test.go

@@ -45,27 +45,6 @@ func TestAnalyzeCommand(t *testing.T) {
 		{name: "sudo dynamic flag then rm -rf", script: `sudo "$maybe" rm -rf /tmp/x`, destructive: true},
 
 		{name: "curl", script: "curl https://example.com", network: true},
-		{name: "PowerShell iwr alias", script: "iwr https://example.com", network: true},
-		{name: "PowerShell irm alias", script: "irm https://example.com", network: true},
-		{name: "PowerShell Invoke-WebRequest", script: "Invoke-WebRequest https://example.com", network: true},
-		{name: "PowerShell Invoke-RestMethod", script: "Invoke-RestMethod https://example.com", network: true},
-		{name: "PowerShell Remove-Item recursive force", script: `Remove-Item -Recurse -Force 'C:\temp\x'`, destructive: true},
-		{name: "PowerShell rm recursive force", script: `rm -Recurse -Force 'C:\temp\x'`, destructive: true},
-		{name: "PowerShell ri recursive force", script: `ri -Recurse -Force 'C:\temp\x'`, destructive: true},
-		{name: "PowerShell rd recursive force", script: `rd -Recurse -Force 'C:\temp\x'`, destructive: true},
-		{name: "PowerShell rmdir recursive force", script: `rmdir -Recurse -Force 'C:\temp\x'`, destructive: true},
-		{name: "PowerShell del recursive force", script: `del -Recurse -Force 'C:\temp\x'`, destructive: true},
-		{name: "PowerShell erase recursive force", script: `erase -Recurse -Force 'C:\temp\x'`, destructive: true},
-		{name: "PowerShell ambiguous force abbreviation", script: `Remove-Item -Recurse -f 'C:\temp\x'`, destructive: false},
-		{name: "PowerShell Remove-Item without recurse", script: `Remove-Item -Force 'C:\temp\x'`, destructive: false},
-		{name: "Windows curl cmd", script: "curl.cmd https://example.com", network: true},
-		{name: "Windows curl exe", script: "curl.exe https://example.com", network: true},
-		{name: "Windows drive path curl exe", script: `'C:\tools\curl.exe' https://example.com`, network: true},
-		{name: "Windows UNC path curl exe", script: `'\\server\share\curl.exe' https://example.com`, network: true},
-		{name: "Windows dot relative path curl exe", script: `'.\curl.exe' https://example.com`, network: true},
-		{name: "Windows relative path curl exe", script: `'tools\curl.exe' https://example.com`, network: true},
-		{name: "Windows drive relative path curl exe", script: `'C:curl.exe' https://example.com`, network: true},
-		{name: "Windows npm cmd", script: "npm.cmd install", network: true},
 		{name: "wget piped to shell", script: "wget -qO- https://x.test | sh", network: true},
 		{name: "python http server", script: "python3 -m http.server 8000", network: true},
 		{name: "python pip install", script: "python3 -m pip install requests", network: true},

internal/sandbox/engine_test.go

@@ -74,25 +74,6 @@ func TestEngineBashAllowGrantDoesNotBypassNetworkPrompt(t *testing.T) {
 	}
 }
 
-func TestEngineClassifiesPowerShellCurlCommandAsNetwork(t *testing.T) {
-	engine := NewEngine(EngineOptions{
-		WorkspaceRoot: t.TempDir(),
-		Policy:        DefaultPolicy(),
-	})
-	decision := engine.Evaluate(context.Background(), Request{
-		ToolName:       "bash",
-		SideEffect:     SideEffectShell,
-		Permission:     PermissionPrompt,
-		PermissionMode: PermissionModeAsk,
-		Args: map[string]any{
-			"command": `$env:PATH = '.;' + $env:PATH; curl.cmd https://example.com`,
-		},
-	})
-	if decision.Action != ActionPrompt || decision.Reason != ReasonNetworkBlocked || !HasRiskCategory(decision.Risk, "network") {
-		t.Fatalf("PowerShell curl command decision = %#v, want network prompt", decision)
-	}
-}
-
 func TestUnsandboxedExecutionAllowedPreservesDeniedReads(t *testing.T) {
 	root := t.TempDir()
 	policy := DefaultPolicy()

internal/sandbox/runner_windows_integration_test.go

@@ -266,74 +266,6 @@ func TestWindowsRestrictedTokenNestedPipeCapture(t *testing.T) {
 	}
 }
 
-// TestWindowsRestrictedTokenPowerShell exercises the default Windows shell
-// shape end to end under the write-restricted token. It covers PowerShell
-// initialization, a native pipeline (which creates IPC objects), UTF-8 output,
-// and workspace write enforcement.
-func TestWindowsRestrictedTokenPowerShell(t *testing.T) {
-	if os.Getenv("ZERO_SANDBOX_REAL_SMOKE") != "1" {
-		t.Skip("set ZERO_SANDBOX_REAL_SMOKE=1 to run real Windows sandbox smoke tests")
-	}
-	runnerExe := realSmokeExecutable(t, "ZERO_WINDOWS_COMMAND_RUNNER_EXE", WindowsSandboxCommandRunnerName)
-	powerShell := realSmokePowerShell(t)
-
-	root := t.TempDir()
-	outside := t.TempDir()
-	sandboxHome := filepath.Join(root, ".zero-sandbox")
-	profile := PermissionProfile{
-		FileSystem: FileSystemPolicy{
-			Kind:                 FileSystemRestricted,
-			ReadRoots:            []string{root},
-			WriteRoots:           []WritableRoot{{Root: root}},
-			IncludePlatformRoots: true,
-			AllowTemp:            true,
-		},
-		Network: NetworkPolicy{Mode: NetworkDeny},
-	}
-	config := WindowsSandboxCommandArgsOptions{
-		SandboxHome:       sandboxHome,
-		CommandCWD:        root,
-		WorkspaceRoots:    []string{root},
-		PermissionProfile: profile,
-		SandboxLevel:      WindowsSandboxLevelUnelevated,
-	}
-
-	insideMarker := filepath.Join(root, "powershell-ok.txt")
-	script := "$ErrorActionPreference='Stop'; " +
-		"[Console]::OutputEncoding=[System.Text.Encoding]::UTF8; " +
-		"$values = 1,2,3 | ForEach-Object { $_ * 2 }; " +
-		"[IO.File]::WriteAllText(" + powershellSingleQuote(insideMarker) + ", (($values -join ',') + ' ✓'))"
-	runWindowsRealSmokeCommand(t, runnerExe, config, []string{
-		powerShell, "-NoLogo", "-NoProfile", "-Command", script,
-	}, 0)
-	if bytes, err := os.ReadFile(insideMarker); err != nil || strings.TrimSpace(string(bytes)) != "2,4,6 ✓" {
-		t.Fatalf("PowerShell sandbox marker = %q, %v; want pipeline output", bytes, err)
-	}
-
-	outsideMarker := filepath.Join(outside, "powershell-denied.txt")
-	deniedScript := "$ErrorActionPreference='Stop'; " +
-		"[IO.File]::WriteAllText(" + powershellSingleQuote(outsideMarker) + ", 'leaked')"
-	runWindowsRealSmokeCommand(t, runnerExe, config, []string{
-		powerShell, "-NoLogo", "-NoProfile", "-Command", deniedScript,
-	}, 1)
-	if _, err := os.Stat(outsideMarker); err == nil {
-		t.Fatal("sandboxed PowerShell wrote outside every granted root")
-	} else if !os.IsNotExist(err) {
-		t.Fatalf("stat outside PowerShell marker: %v", err)
-	}
-}
-
-func realSmokePowerShell(t *testing.T) string {
-	t.Helper()
-	for _, candidate := range []string{"pwsh.exe", "pwsh", "powershell.exe", "powershell"} {
-		if path, err := exec.LookPath(candidate); err == nil {
-			return path
-		}
-	}
-	t.Skip("PowerShell is unavailable")
-	return ""
-}
-
 func realSmokeExecutable(t *testing.T, envKey string, fallbackName string) string {
 	t.Helper()
 	if path := os.Getenv(envKey); path != "" {

internal/sandbox/safe_command.go

@@ -430,70 +430,25 @@ func shellDashCPayload(program string, fields []string) string {
 // name: it strips shell quoting/escaping characters (", ', `, \) wherever they
 // appear in the token (including embedded ones like `vi\m` or `v"i"m`), strips
 // leading command-substitution markers, removes any directory prefix (so
-// /usr/bin/vim and C:\tools\vim.exe match "vim"), removes Windows executable
-// suffixes, and lowercases. This closes path/quote/substitution evasions of the
-// detector and keeps curl.exe/npm.cmd equivalent to curl/npm for risk analysis.
+// /usr/bin/vim and C:\tools\vim.exe match "vim"), and lowercases. This closes
+// path/quote/substitution evasions of the detector.
 func normalizeProgramToken(field string) string {
 	token := strings.TrimSpace(field)
 	token = strings.TrimLeft(token, "$(")
 	token = strings.TrimRight(token, ")")
-	// PowerShell commonly invokes drive-letter, UNC, and relative paths. Extract
-	// their basename while backslashes still carry path-separator meaning;
-	// removing them first would turn C:\tools\curl.exe into c:toolscurl.exe and
-	// bypass the canonical curl risk entry.
-	pathToken := stripChars(token, "\"'`")
-	if windowsPathBasename, ok := windowsExecutablePathBasename(pathToken); ok {
-		token = windowsPathBasename
-	} else {
-		// Strip shell quoting/escaping characters (", ', `, \) wherever they
-		// appear in the token — surrounding, embedded, or as a mid-word escape
-		// — so "vim", v"i"m, 'v'im, and vi\m all collapse to the program name.
-		token = stripChars(token, "\"'`\\")
-		// Strip a directory prefix so /usr/bin/vim reduces to the basename.
-		if i := strings.LastIndex(token, "/"); i >= 0 {
-			token = token[i+1:]
-		}
+	// Strip shell quoting/escaping characters (", ', `, \) wherever they appear
+	// in the token — surrounding, embedded, or as a mid-word escape — so
+	// "vim", v"i"m, 'v'im, and vi\m all collapse to the program name. This is
+	// done BEFORE the directory-prefix trim so an escape can't masquerade as a
+	// path separator (e.g. vi\m must become vim, not m).
+	token = stripChars(token, "\"'`\\")
+	// Strip a directory prefix so /usr/bin/vim reduces to the basename. (A
+	// Windows-style backslash path separator is already removed above, so only
+	// the POSIX separator remains to split on.)
+	if i := strings.LastIndex(token, "/"); i >= 0 {
+		token = token[i+1:]
 	}
-	token = strings.ToLower(token)
-	for _, suffix := range []string{".exe", ".cmd", ".bat", ".com"} {
-		if strings.HasSuffix(token, suffix) {
-			return strings.TrimSuffix(token, suffix)
-		}
-	}
-	return token
-}
-
-func windowsExecutablePathBasename(token string) (string, bool) {
-	drivePath := len(token) >= 3 &&
-		((token[0] >= 'a' && token[0] <= 'z') || (token[0] >= 'A' && token[0] <= 'Z')) &&
-		token[1] == ':'
-	uncPath := strings.HasPrefix(token, `\\`)
-	explicitRelativePath := strings.HasPrefix(token, `.\`) || strings.HasPrefix(token, `..\`)
-	backslashRelativePath := strings.ContainsRune(token, '\\') && hasWindowsExecutableSuffix(token)
-	if !drivePath && !uncPath && !explicitRelativePath && !backslashRelativePath {
-		return "", false
-	}
-	index := strings.LastIndexAny(token, `\/`)
-	if index >= 0 {
-		if index+1 >= len(token) {
-			return "", false
-		}
-		return token[index+1:], true
-	}
-	if drivePath && len(token) > 2 {
-		return token[2:], true
-	}
-	return "", false
-}
-
-func hasWindowsExecutableSuffix(token string) bool {
-	token = strings.ToLower(token)
-	for _, suffix := range []string{".exe", ".cmd", ".bat", ".com"} {
-		if strings.HasSuffix(token, suffix) {
-			return true
-		}
-	}
-	return false
+	return strings.ToLower(token)
 }
 
 // stripChars returns s with every rune in cutset removed.

internal/tools/bash.go

@@ -106,7 +106,7 @@ func (tool bashTool) run(ctx context.Context, args map[string]any, engine *zeroS
 	// unsandboxed) can actually bypass the MSYS guard instead of being
 	// hard-blocked by the same check it was meant to escalate past.
 	commandEngine := commandEngineForSandboxPermissions(engine, sandboxPermissions)
-	if issue := detectShellCommandIssueForRuntime(commandText, detectShellRuntime(runtime.GOOS)); issue != nil && !msysGuardBypassed(issue, commandEngine) {
+	if issue := detectShellCommandIssue(commandText, runtime.GOOS); issue != nil && !msysGuardBypassed(issue, commandEngine) {
 		return shellIssueBlockResult(*issue)
 	}
 
@@ -293,19 +293,23 @@ func shellIssueBlockResult(issue shellIssue) Result {
 }
 
 // buildBashCommand returns the exec.Cmd and the sandbox plan for running
-// commandText. PowerShell is preferred on Windows, with cmd.exe retained as
-// the fallback. Only cmd.exe needs the raw command-line override.
+// commandText. On Windows, when the command is not wrapped by the sandbox
+// engine (plan.Wrapped == false), it also overrides the child's raw command
+// line so commandText reaches cmd.exe unescaped; see
+// zeroSandbox.WindowsShellCommandLine for why that matters. The wrapped case
+// gets the same treatment inside the sandboxed runner process itself
+// (internal/sandbox/windows_process_windows.go), since that command line is
+// built there, not here.
 func buildBashCommand(ctx context.Context, commandText string, absoluteCwd string, engine *zeroSandbox.Engine) (*exec.Cmd, zeroSandbox.CommandPlan, error) {
-	hostShell := detectShellRuntime(runtime.GOOS)
 	spec := zeroSandbox.CommandSpec{
-		Name: hostShell.Executable,
-		Args: hostShell.arguments(commandText),
+		Name: shellExecutable(),
+		Args: shellArguments(commandText),
 		Dir:  absoluteCwd,
 	}
 	if engine != nil {
 		command, plan, err := engine.CommandContext(ctx, spec)
 		if err == nil {
-			applyWindowsShellCommandLine(command, commandText, plan.Wrapped, hostShell.Kind == shellKindCmd)
+			applyWindowsShellCommandLine(command, commandText, plan.Wrapped)
 		}
 		return command, plan, err
 	}
@@ -329,7 +333,7 @@ func buildBashCommand(ctx context.Context, commandText string, absoluteCwd strin
 	}
 	command := exec.CommandContext(ctx, spec.Name, spec.Args...)
 	command.Dir = spec.Dir
-	applyWindowsShellCommandLine(command, commandText, plan.Wrapped, hostShell.Kind == shellKindCmd)
+	applyWindowsShellCommandLine(command, commandText, plan.Wrapped)
 	return command, plan, nil
 }
 
@@ -381,6 +385,20 @@ func interactiveBlockResult(detection zeroSandbox.InteractiveCommandResult) Resu
 	}
 }
 
+func shellExecutable() string {
+	if runtime.GOOS == "windows" {
+		return "cmd.exe"
+	}
+	return "/bin/sh"
+}
+
+func shellArguments(command string) []string {
+	if runtime.GOOS == "windows" {
+		return zeroSandbox.WindowsShellArgs(command)
+	}
+	return []string{"-c", command}
+}
+
 func commandExitCode(err error) int {
 	if err == nil {
 		return 0
@@ -603,7 +621,7 @@ func truncateHeadTailWithTotal(value string, total, maxBytes int) (string, int,
 
 func formatBashOutputWithShellHint(stdout string, stderr string, exitCode int, meta map[string]string) string {
 	output := formatBashOutput(stdout, stderr, exitCode)
-	if issue := detectShellOutputIssueForRuntime(stdout+"\n"+stderr, detectShellRuntime(runtime.GOOS)); issue != nil {
+	if issue := detectShellOutputIssue(stdout+"\n"+stderr, runtime.GOOS); issue != nil {
 		meta["shell_issue"] = issue.Kind
 		output = appendShellIssueHint(output, *issue)
 	}

internal/tools/bash_proc_unix.go

@@ -36,6 +36,6 @@ func hardenProcessLifetime(command *exec.Cmd) {
 	}
 }
 
-// applyWindowsShellCommandLine is a no-op outside Windows.
-func applyWindowsShellCommandLine(command *exec.Cmd, commandText string, wrapped bool, cmdFallback bool) {
-}
+// applyWindowsShellCommandLine is a no-op outside Windows; there is no
+// cmd.exe command-line-parsing quirk to work around here.
+func applyWindowsShellCommandLine(command *exec.Cmd, commandText string, wrapped bool) {}

internal/tools/bash_proc_windows.go

@@ -31,12 +31,15 @@ func hardenProcessLifetime(command *exec.Cmd) {
 	}
 }
 
-// applyWindowsShellCommandLine overrides the cmd.exe fallback's raw child
-// command line so commandText reaches cmd.exe unescaped. PowerShell consumes
-// ordinary argv quoting and must not take this path. Wrapped commands are
-// handled after unwrapping by the Windows sandbox runner.
-func applyWindowsShellCommandLine(command *exec.Cmd, commandText string, wrapped bool, cmdFallback bool) {
-	if wrapped || !cmdFallback {
+// applyWindowsShellCommandLine overrides command's raw child command line so
+// commandText reaches cmd.exe unescaped instead of auto-quoted the way
+// exec.Cmd would normally encode a single Args element. Skipped when wrapped
+// is true: the sandbox engine then routes execution through a separate
+// zero-windows-command-runner process, which builds its own child command
+// line from scratch (internal/sandbox/windows_process_windows.go) rather than
+// inheriting whatever this outer exec.Cmd is configured with.
+func applyWindowsShellCommandLine(command *exec.Cmd, commandText string, wrapped bool) {
+	if wrapped {
 		return
 	}
 	command.SysProcAttr = &syscall.SysProcAttr{CmdLine: zeroSandbox.WindowsShellCommandLine(commandText)}

internal/tools/bash_tool_test.go

@@ -124,15 +124,11 @@ func TestBashToolDescribesHostShellSyntax(t *testing.T) {
 	}
 
 	if runtime.GOOS == "windows" {
-		shell := detectShellRuntime(runtime.GOOS)
-		if shell.Kind == shellKindPowerShell {
-			for _, want := range []string{"powershell", "cwd", "get-childitem", "select-string", "$env:name"} {
-				if !strings.Contains(description, want) {
-					t.Fatalf("expected Windows PowerShell guidance %q in bash description, got %q", want, description)
-				}
-			}
-		} else if !strings.Contains(description, "cmd.exe") || !strings.Contains(description, "cwd") {
-			t.Fatalf("expected Windows cmd.exe fallback guidance in bash description, got %q", description)
+		if !strings.Contains(description, "cmd.exe") || !strings.Contains(description, "cwd") {
+			t.Fatalf("expected Windows cmd.exe and cwd guidance in bash description, got %q", description)
+		}
+		if !strings.Contains(description, "double quotes") || !strings.Contains(description, `--jq ".a | b"`) {
+			t.Fatalf("expected the double-quote metacharacter rule in bash description, got %q", description)
 		}
 		return
 	}
@@ -459,14 +455,13 @@ func TestBashToolReturnsNonzeroExitAsError(t *testing.T) {
 	if result.Status != StatusError {
 		t.Fatalf("expected error status, got %s", result.Status)
 	}
-	wantExitCode := strconv.Itoa(helperFailureExitCode())
-	for _, want := range []string{"stdout:\nbefore failure", "stderr:\nfailure details", "exit_code: " + wantExitCode} {
+	for _, want := range []string{"stdout:\nbefore failure", "stderr:\nfailure details", "exit_code: 7"} {
 		if !strings.Contains(result.Output, want) {
 			t.Fatalf("expected output to contain %q, got %q", want, result.Output)
 		}
 	}
-	if result.Meta["exit_code"] != wantExitCode {
-		t.Fatalf("expected exit_code metadata %s, got %q", wantExitCode, result.Meta["exit_code"])
+	if result.Meta["exit_code"] != "7" {
+		t.Fatalf("expected exit_code metadata 7, got %q", result.Meta["exit_code"])
 	}
 	if result.ExecutionOutcome == nil || result.ExecutionOutcome.State != execution.StateFailed || result.ExecutionOutcome.Kind != execution.OutcomeApplicationFailure {
 		t.Fatalf("execution outcome = %#v, want failed/application_failure", result.ExecutionOutcome)
@@ -583,16 +578,10 @@ func TestBashToolRequireEscalatedMsysGuard(t *testing.T) {
 	}
 	registry := NewRegistry()
 	registry.Register(NewScopedBashTool(root, nil))
-	msysCommand := "cat somefile.txt"
-	if detectShellRuntime(runtime.GOOS).Kind == shellKindPowerShell {
-		// cat is a native Get-Content alias in PowerShell. Use a name that
-		// still resolves to an incompatible Git-for-Windows MSYS executable.
-		msysCommand = "grep pattern somefile.txt"
-	}
 
 	t.Run("default sandboxing still blocks an MSYS-prone command", func(t *testing.T) {
 		result := registry.RunWithOptions(context.Background(), "bash", map[string]any{
-			"command": msysCommand,
+			"command": "cat somefile.txt",
 		}, RunOptions{
 			PermissionGranted: true,
 			Sandbox:           newEngine(),
@@ -605,7 +594,7 @@ func TestBashToolRequireEscalatedMsysGuard(t *testing.T) {
 
 	t.Run("approved require_escalated bypasses the MSYS guard", func(t *testing.T) {
 		result := registry.RunWithOptions(context.Background(), "bash", map[string]any{
-			"command":             msysCommand,
+			"command":             "cat somefile.txt",
 			"sandbox_permissions": string(SandboxPermissionsRequireEscalated),
 		}, RunOptions{
 			PermissionGranted: true,
@@ -659,9 +648,8 @@ func TestBashToolIgnoresMsysMarkersInCommandArgumentsAfterFailure(t *testing.T)
 		"command": command,
 	})
 
-	wantExitCode := strconv.Itoa(helperFailureExitCode())
-	if result.Status != StatusError || result.Meta["exit_code"] != wantExitCode {
-		t.Fatalf("expected the helper failure exit %s, got %s: %#v", wantExitCode, result.Status, result)
+	if result.Status != StatusError || result.Meta["exit_code"] != "7" {
+		t.Fatalf("expected the helper's real exit 7 failure, got %s: %#v", result.Status, result)
 	}
 	if result.Meta["shell_issue"] == "windows_msys_sandbox" {
 		t.Fatalf("expected the MSYS marker in the command's own argument text to be ignored, got %#v", result)
@@ -872,9 +860,6 @@ func TestBashToolRunsCommandLineForLoopSyntax(t *testing.T) {
 	if runtime.GOOS != "windows" {
 		t.Skip("cmd.exe command-line vs batch-file parsing is Windows-specific")
 	}
-	if detectShellRuntime(runtime.GOOS).Kind != shellKindCmd {
-		t.Skip("cmd.exe fallback is not selected")
-	}
 	root := t.TempDir()
 
 	result := NewScopedBashTool(root, nil).Run(context.Background(), map[string]any{
@@ -896,10 +881,6 @@ func helperCommand(name string) string {
 	return executable + " --zero-bash-helper " + name
 }
 
-func helperFailureExitCode() int {
-	return 7
-}
-
 func shellQuote(value string) string {
 	if runtime.GOOS == "windows" {
 		return value

internal/tools/exec_command.go

@@ -173,7 +173,7 @@ func (tool execCommandTool) run(ctx context.Context, args map[string]any, engine
 	// unsandboxed) can actually bypass the MSYS guard instead of being
 	// hard-blocked by the same check it was meant to escalate past.
 	commandEngine := commandEngineForSandboxPermissions(engine, sandboxPermissions)
-	if issue := detectShellCommandIssueForRuntime(commandText, detectShellRuntime(runtimeGOOS())); issue != nil && !msysGuardBypassed(issue, commandEngine) {
+	if issue := detectShellCommandIssue(commandText, runtimeGOOS()); issue != nil && !msysGuardBypassed(issue, commandEngine) {
 		return shellIssueBlockResult(*issue)
 	}
 	if interactive := zeroSandbox.DetectInteractiveCommand(commandText, runtimeGOOS()); interactive.Interactive {
@@ -459,7 +459,7 @@ func execToolResultWithBudget(input execToolResultInput, directBudget bool) Resu
 	}
 	body := formatExecCommandOutput(output, input.sessionID, input.exited, input.exitCode, input.interrupted)
 	if status == StatusError && input.exited && !input.interrupted {
-		if issue := detectShellOutputIssueForRuntime(output, detectShellRuntime(runtimeGOOS())); issue != nil {
+		if issue := detectShellOutputIssue(output, runtimeGOOS()); issue != nil {
 			meta["shell_issue"] = issue.Kind
 			body = appendShellIssueHint(body, *issue)
 		}

internal/tools/exec_command_test.go

@@ -76,15 +76,11 @@ func TestExecCommandToolDescribesHostShellSyntax(t *testing.T) {
 	description := strings.ToLower(strings.Join(descriptionParts, " "))
 
 	if runtime.GOOS == "windows" {
-		shell := detectShellRuntime(runtime.GOOS)
-		if shell.Kind == shellKindPowerShell {
-			for _, want := range []string{"powershell", "cwd", "get-childitem", "select-string", "$env:name"} {
-				if !strings.Contains(description, want) {
-					t.Fatalf("expected Windows PowerShell guidance %q in exec_command description, got %q", want, description)
-				}
-			}
-		} else if !strings.Contains(description, "cmd.exe") || !strings.Contains(description, "cwd") {
-			t.Fatalf("expected Windows cmd.exe fallback guidance in exec_command description, got %q", description)
+		if !strings.Contains(description, "cmd.exe") || !strings.Contains(description, "cwd") {
+			t.Fatalf("expected Windows cmd.exe and cwd guidance in exec_command description, got %q", description)
+		}
+		if !strings.Contains(description, "double quotes") || !strings.Contains(description, `--jq ".a | b"`) {
+			t.Fatalf("expected the double-quote metacharacter rule in exec_command description, got %q", description)
 		}
 	}
 }
@@ -196,15 +192,9 @@ func TestExecCommandRequireEscalatedBypassesMsysGuardAfterApproval(t *testing.T)
 		Policy:        sandbox.DefaultPolicy(),
 		Backend:       sandbox.Backend{Name: sandbox.BackendUnavailable, Message: "native sandbox unavailable"},
 	})
-	msysCommand := "cat somefile.txt"
-	if detectShellRuntime(runtime.GOOS).Kind == shellKindPowerShell {
-		// cat is a native Get-Content alias in PowerShell, so use an executable
-		// name that still exercises the MSYS guard.
-		msysCommand = "grep pattern somefile.txt"
-	}
 
 	result := registry.RunWithOptions(context.Background(), ExecCommandToolName, map[string]any{
-		"cmd":                 msysCommand,
+		"cmd":                 "cat somefile.txt",
 		"sandbox_permissions": string(SandboxPermissionsRequireEscalated),
 	}, RunOptions{
 		PermissionGranted: true,
@@ -214,8 +204,8 @@ func TestExecCommandRequireEscalatedBypassesMsysGuardAfterApproval(t *testing.T)
 
 	// Assert on the preflight block sentinel (exit_code "-1", set only by
 	// shellIssueBlockResult) rather than shell_issue: once the guard is
-	// bypassed, the command actually runs, and its real, PATH-dependent output
-	// could otherwise trip the unrelated
+	// bypassed, "cat somefile.txt" actually runs, and its real,
+	// PATH-dependent output could otherwise trip the unrelated
 	// post-execution detectShellOutputIssue heuristic and make this
 	// assertion flaky for reasons unrelated to the guard under test.
 	if result.Meta["exit_code"] == "-1" {
@@ -294,9 +284,8 @@ func TestExecCommandApplicationFailureHasTypedOutcome(t *testing.T) {
 	if result.ExecutionOutcome == nil || result.ExecutionOutcome.State != execution.StateFailed || result.ExecutionOutcome.Kind != execution.OutcomeApplicationFailure {
 		t.Fatalf("execution outcome = %#v, want failed/application_failure", result.ExecutionOutcome)
 	}
-	wantExitCode := helperFailureExitCode()
-	if result.ExecutionOutcome.Exit == nil || result.ExecutionOutcome.Exit.Code != wantExitCode {
-		t.Fatalf("execution exit = %#v, want code %d", result.ExecutionOutcome.Exit, wantExitCode)
+	if result.ExecutionOutcome.Exit == nil || result.ExecutionOutcome.Exit.Code != 7 {
+		t.Fatalf("execution exit = %#v, want code 7", result.ExecutionOutcome.Exit)
 	}
 }
 

internal/tools/shell_runtime.go

@@ -1,33 +1,15 @@
 package tools
 
 import (
-	"context"
-	"os"
-	"os/exec"
-	"path/filepath"
 	"regexp"
-	"runtime"
 	"strings"
-	"sync"
-	"time"
 	"unicode"
-
-	zeroSandbox "github.com/Gitlawb/zero/internal/sandbox"
-)
-
-type shellKind string
-
-const (
-	shellKindPOSIX      shellKind = "posix"
-	shellKindPowerShell shellKind = "powershell"
-	shellKindCmd        shellKind = "cmd"
 )
 
 type shellRuntime struct {
 	GOOS       string
 	Executable string
 	Syntax     string
-	Kind       shellKind
 }
 
 type shellIssue struct {
@@ -38,18 +20,7 @@ type shellIssue struct {
 
 const windowsMsysSandboxKind = "windows_msys_sandbox"
 
-const windowsMsysSandboxSuggestion = "MSYS/Cygwin executables and shells (bash, sh) from Git for Windows cannot run under Zero's write-restricted Windows sandbox, and the WSL bash launcher cannot reach the WSL service from it either. This also hits native commands that spawn Git Bash internally: git hooks and git/gh credential helpers can fail this way even though git and gh themselves run fine. Prefer native PowerShell cmdlets or Zero tools (grep, read_file with offset/limit, list_directory, glob). If host-level execution is truly required, rerun with sandbox_permissions: \"require_escalated\" and a narrow justification."
-
-const windowsPowerShellUTF8Prefix = "try { [Console]::OutputEncoding = [System.Text.Encoding]::UTF8 } catch {}\n"
-
-const windowsPowerShellFailurePrefix = "$ErrorActionPreference = 'Stop'\n"
-
-const windowsPowerShellExitSuffix = "\nif ($null -ne $LASTEXITCODE) { exit $LASTEXITCODE }\n"
-
-var (
-	hostShellOnce sync.Once
-	hostShell     shellRuntime
-)
+const windowsMsysSandboxSuggestion = "MSYS/Cygwin coreutils and shells (bash, sh) from Git for Windows cannot run under Zero's write-restricted Windows sandbox, and the WSL bash launcher cannot reach the WSL service from it either. This also hits native commands that spawn Git Bash internally: git hooks and git/gh credential helpers can fail this way even though git and gh themselves run fine. Prefer Zero native tools (grep, read_file with offset/limit, list_directory, glob), cmd.exe findstr, or PowerShell Select-Object -First/-Last. If host-level execution is truly required, rerun with sandbox_permissions: \"require_escalated\" and a narrow justification."
 
 // windowsMsysProneNames is the single source of truth for POSIX coreutil and
 // shell names that commonly resolve to a Git-for-Windows MSYS/Cygwin binary
@@ -83,139 +54,24 @@ var (
 )
 
 func detectShellRuntime(goos string) shellRuntime {
-	if goos != runtime.GOOS {
-		return detectShellRuntimeWithLookup(goos, exec.LookPath, os.Getenv)
-	}
-	hostShellOnce.Do(func() {
-		hostShell = detectShellRuntimeWithProbe(goos, exec.LookPath, os.Getenv, powerShellExecutableUsable)
-	})
-	return hostShell
-}
-
-func detectShellRuntimeWithLookup(goos string, lookPath func(string) (string, error), getenv func(string) string) shellRuntime {
-	return detectShellRuntimeWithProbe(goos, lookPath, getenv, func(string) bool { return true })
-}
-
-func detectShellRuntimeWithProbe(goos string, lookPath func(string) (string, error), getenv func(string) string, usable func(string) bool) shellRuntime {
 	if goos == "windows" {
-		for _, candidate := range windowsPowerShellCandidates(getenv) {
-			if path, err := lookPath(candidate); err == nil && strings.TrimSpace(path) != "" && usable(path) {
-				return shellRuntime{
-					GOOS:       goos,
-					Executable: path,
-					Syntax:     "PowerShell",
-					Kind:       shellKindPowerShell,
-				}
-			}
-		}
-		return shellRuntime{GOOS: goos, Executable: "cmd.exe", Syntax: "Windows cmd.exe", Kind: shellKindCmd}
+		return shellRuntime{GOOS: goos, Executable: "cmd.exe", Syntax: "Windows cmd.exe"}
 	}
-	return shellRuntime{GOOS: goos, Executable: "/bin/sh", Syntax: "/bin/sh", Kind: shellKindPOSIX}
-}
-
-func powerShellExecutableUsable(path string) bool {
-	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
-	defer cancel()
-	command := exec.CommandContext(ctx, path, "-NoLogo", "-NoProfile", "-Command", "exit 0")
-	return command.Run() == nil
-}
-
-func windowsPowerShellCandidates(getenv func(string) string) []string {
-	candidates := []string{"pwsh.exe", "pwsh"}
-	if programFiles := strings.TrimSpace(getenv("ProgramFiles")); programFiles != "" {
-		candidates = append(candidates, filepath.Join(programFiles, "PowerShell", "7", "pwsh.exe"))
-	}
-	candidates = append(candidates, "powershell.exe", "powershell")
-	if systemRoot := strings.TrimSpace(getenv("SystemRoot")); systemRoot != "" {
-		candidates = append(candidates, filepath.Join(systemRoot, "System32", "WindowsPowerShell", "v1.0", "powershell.exe"))
-	}
-	return candidates
-}
-
-func (shell shellRuntime) arguments(command string) []string {
-	switch shell.Kind {
-	case shellKindPowerShell:
-		script := windowsPowerShellUTF8Prefix + windowsPowerShellFailurePrefix + command + windowsPowerShellExitSuffix
-		return []string{"-NoLogo", "-NoProfile", "-Command", script}
-	case shellKindCmd:
-		return zeroSandbox.WindowsShellArgs(command)
-	default:
-		return []string{"-c", command}
-	}
-}
-
-// HostShellCommand returns the shell executable and argv used for a command on
-// this host. Keeping this in one place makes agent tools and the user-typed TUI
-// shell escape use the same Windows shell and fallback behavior.
-func HostShellCommand(command string) (string, []string) {
-	shell := detectShellRuntime(runtime.GOOS)
-	return shell.Executable, shell.arguments(command)
-}
-
-// NewHostShellCommandContext constructs a direct host-shell command. The
-// cmd.exe fallback needs a Windows-specific raw command line, while PowerShell
-// and POSIX shells use normal argv handling.
-func NewHostShellCommandContext(ctx context.Context, commandText string) *exec.Cmd {
-	shell := detectShellRuntime(runtime.GOOS)
-	command := exec.CommandContext(ctx, shell.Executable, shell.arguments(commandText)...)
-	applyWindowsShellCommandLine(command, commandText, false, shell.Kind == shellKindCmd)
-	return command
+	return shellRuntime{GOOS: goos, Executable: "/bin/sh", Syntax: "/bin/sh"}
 }
 
 func shellGuidanceForGOOS(goos string) string {
-	return shellGuidanceForRuntime(detectShellRuntime(goos))
-}
-
-func shellGuidanceForRuntime(shell shellRuntime) string {
-	if shell.GOOS == "windows" && shell.Kind == shellKindPowerShell {
-		guidance := "Uses PowerShell syntax on Windows; prefer cwd/workdir over Set-Location when changing directories. Examples: Get-ChildItem -Force; Get-ChildItem -Recurse -Filter *.go; Get-ChildItem -Recurse | Select-String -Pattern 'TODO'; Get-Process | Where-Object { $_.ProcessName -like '*node*' }; $env:NAME='value'; @'\nprint('hello')\n'@ | python -. Do not invoke Git-for-Windows MSYS/Cygwin executables (bash, sh, grep.exe, sed.exe, head.exe, and similar) inside the restricted sandbox; prefer PowerShell cmdlets or native Zero tools."
-		return guidance + legacyPowerShellChainGuidance(shell)
+	runtime := detectShellRuntime(goos)
+	if goos == "windows" {
+		return "Uses " + runtime.Syntax + " syntax on Windows; prefer cwd over cd when changing directories. To include | & > < or other metacharacters in an argument value, wrap the value in double quotes (e.g. --jq \".a | b\"); single quotes do not protect metacharacters in cmd.exe. MSYS/Cygwin coreutils on PATH (Git for Windows usr\\bin) are not sandbox-compatible; prefer native Zero file tools."
 	}
-	if shell.GOOS == "windows" {
-		return "Uses " + shell.Syntax + " syntax on Windows because PowerShell was unavailable; prefer cwd/workdir over cd when changing directories. To include | & > < or other metacharacters in an argument value, wrap the value in double quotes (e.g. --jq \".a | b\"); single quotes do not protect metacharacters in cmd.exe. MSYS/Cygwin coreutils on PATH (Git for Windows usr\\bin) are not sandbox-compatible; prefer native Zero file tools."
-	}
-	guidance := "Uses " + shell.Syntax + " syntax."
-	if shell.GOOS == "darwin" {
+	guidance := "Uses " + runtime.Syntax + " syntax."
+	if goos == "darwin" {
 		guidance += " To find or stop a process, use `lsof -i :PORT` (or `lsof -nP -iTCP -sTCP:LISTEN`) for the PID then `kill <pid>`; `ps` and `pgrep` do not work under the sandbox."
 	}
 	return guidance
 }
 
-// HostShellEnvironmentGuidance returns the concise, model-facing shell rule
-// for the current host.
-func HostShellEnvironmentGuidance() string {
-	return hostShellEnvironmentGuidanceForRuntime(detectShellRuntime(runtime.GOOS))
-}
-
-func hostShellEnvironmentGuidanceForRuntime(shell shellRuntime) string {
-	if shell.GOOS == "windows" && shell.Kind == shellKindPowerShell {
-		guidance := "Shell syntax: PowerShell for exec_command/bash tools. Use PowerShell cmdlets and pipelines (Get-ChildItem, Get-Content, Select-String, Select-Object), use $env:NAME='value' for environment variables, and prefer the workdir/cwd argument over Set-Location. Do not invoke Git-for-Windows MSYS binaries (bash, sh, grep.exe, sed.exe, head.exe, and similar) inside the restricted sandbox; use native PowerShell cmdlets or Zero tools instead, or sandbox_permissions require_escalated only when host-level execution is truly required."
-		return guidance + legacyPowerShellChainGuidance(shell)
-	}
-	if shell.GOOS == "windows" {
-		return "Shell syntax: Windows cmd.exe syntax for exec_command/bash tools because PowerShell is unavailable. To put | & > < etc inside an arg value, use double quotes around the value, not single quotes. Do not invoke Git-for-Windows MSYS binaries inside the restricted sandbox; use native Zero tools instead. Prefer the workdir/cwd argument over cd."
-	}
-	return "Shell syntax: /bin/sh syntax for exec_command/bash tools; prefer the workdir/cwd argument instead of cd when changing directories."
-}
-
-func legacyPowerShellChainGuidance(shell shellRuntime) string {
-	if !shell.isWindowsPowerShell() {
-		return ""
-	}
-	return " This host uses Windows PowerShell 5.1, which does not support && or ||. Use separate statements when execution is unconditional, or if ($?) { ... } and if (-not $?) { ... } for conditional chaining."
-}
-
-func (shell shellRuntime) isWindowsPowerShell() bool {
-	if shell.Kind != shellKindPowerShell {
-		return false
-	}
-	executable := strings.TrimSpace(shell.Executable)
-	if index := strings.LastIndexAny(executable, `\/`); index >= 0 {
-		executable = executable[index+1:]
-	}
-	return strings.EqualFold(executable, "powershell") || strings.EqualFold(executable, "powershell.exe")
-}
-
 // MsysProneCommandName reports whether a bare command name commonly resolves to
 // a Git-for-Windows MSYS binary that fails under the Windows restricted sandbox.
 func MsysProneCommandName(name string) bool {
@@ -316,15 +172,7 @@ func msysProneCommandWord(word string) bool {
 }
 
 func detectShellCommandIssue(command string, goos string) *shellIssue {
-	shell := shellRuntime{GOOS: goos, Executable: "/bin/sh", Syntax: "/bin/sh", Kind: shellKindPOSIX}
-	if goos == "windows" {
-		shell = shellRuntime{GOOS: goos, Executable: "cmd.exe", Syntax: "Windows cmd.exe", Kind: shellKindCmd}
-	}
-	return detectShellCommandIssueForRuntime(command, shell)
-}
-
-func detectShellCommandIssueForRuntime(command string, shell shellRuntime) *shellIssue {
-	if shell.GOOS != "windows" {
+	if goos != "windows" {
 		return nil
 	}
 	trimmed := strings.TrimSpace(command)
@@ -336,24 +184,7 @@ func detectShellCommandIssueForRuntime(command string, shell shellRuntime) *shel
 	// cat), so an escaped metachar can't stand in as a fake segment boundary
 	// either.
 	unquoted := stripCmdCaretEscapes(stripDoubleQuotedSpans(trimmed))
-	if shell.Kind == shellKindPowerShell {
-		unquoted = stripPowerShellQuotedSpans(trimmed)
-		if shell.isWindowsPowerShell() && (strings.Contains(unquoted, "&&") || strings.Contains(unquoted, "||")) {
-			return &shellIssue{
-				Kind:       "windows_powershell_version",
-				Message:    "Command uses && or ||, but this host runs Windows PowerShell 5.1, which does not support those operators.",
-				Suggestion: "Use separate statements when execution is unconditional, or if ($?) { ... } and if (-not $?) { ... } for conditional chaining.",
-			}
-		}
-	}
 	if windowsBashStyleCDPattern.MatchString(unquoted) {
-		if shell.Kind == shellKindPowerShell {
-			return &shellIssue{
-				Kind:       "windows_shell_syntax",
-				Message:    "Command looks like POSIX/Bash syntax, but Zero runs PowerShell commands on this Windows host.",
-				Suggestion: "Use the cwd/workdir argument instead of cd and use native PowerShell syntax or Zero tools such as list_directory, read_file, grep, and glob.",
-			}
-		}
 		return &shellIssue{
 			Kind:       "windows_shell_syntax",
 			Message:    "Command looks like POSIX/Bash syntax, but Zero runs bash tool commands through Windows cmd.exe on this host.",
@@ -367,128 +198,18 @@ func detectShellCommandIssueForRuntime(command string, shell shellRuntime) *shel
 	// Being segment/word anchored rather than a whole-string regex or scan,
 	// neither check matches text that only appears inside a quoted argument
 	// (e.g. a commit message or PR comment body discussing head.exe).
-	segments := windowsCommandSegments(trimmed)
-	if shell.Kind == shellKindPowerShell {
-		segments = powerShellCommandSegments(trimmed)
-	}
-	for _, segment := range segments {
+	for _, segment := range windowsCommandSegments(trimmed) {
 		word := firstCommandWord(segment)
 		if windowsMsysBinaryPathPattern.MatchString(word) {
 			return windowsMsysSandboxIssue("Command invokes an MSYS/Cygwin binary path that cannot run under Zero's Windows sandbox.")
 		}
 		if msysProneCommandWord(word) {
-			if shell.Kind == shellKindPowerShell && powerShellAliasWord(word) {
-				continue
-			}
 			return windowsMsysSandboxIssue("Command uses a POSIX coreutil (head/tail/grep/cat/...) that commonly resolves to Git-for-Windows MSYS binaries incompatible with the Windows sandbox.")
 		}
 	}
 	return nil
 }
 
-// powerShellCommandSegments splits the subset of PowerShell syntax needed for
-// command-position checks. It respects single/double quoted strings and the
-// backtick escape, then splits on pipeline/statement operators. Complex script
-// interpretation remains PowerShell's job; this scanner only determines
-// whether a known-incompatible MSYS executable is actually invoked.
-func powerShellCommandSegments(command string) []string {
-	var segments []string
-	var current strings.Builder
-	var quote rune
-	escaped := false
-	for _, c := range command {
-		if escaped {
-			current.WriteRune(c)
-			escaped = false
-			continue
-		}
-		if c == '`' {
-			current.WriteRune(c)
-			escaped = true
-			continue
-		}
-		if quote != 0 {
-			current.WriteRune(c)
-			if c == quote {
-				quote = 0
-			}
-			continue
-		}
-		if c == '\'' || c == '"' {
-			quote = c
-			current.WriteRune(c)
-			continue
-		}
-		if c == ';' || c == '|' || c == '&' {
-			if segment := strings.TrimSpace(current.String()); segment != "" {
-				segments = append(segments, segment)
-			}
-			current.Reset()
-			continue
-		}
-		current.WriteRune(c)
-	}
-	if segment := strings.TrimSpace(current.String()); segment != "" {
-		segments = append(segments, segment)
-	}
-	return segments
-}
-
-func powerShellAliasWord(word string) bool {
-	trimmed := strings.Trim(word, `"'`)
-	if strings.ContainsAny(trimmed, `\/`) || strings.HasSuffix(strings.ToLower(trimmed), ".exe") {
-		return false
-	}
-	switch strings.ToLower(trimmed) {
-	case "cat", "ls":
-		return true
-	default:
-		return false
-	}
-}
-
-func stripPowerShellQuotedSpans(command string) string {
-	var b strings.Builder
-	b.Grow(len(command))
-	var quote rune
-	escaped := false
-	runes := []rune(command)
-	for index := 0; index < len(runes); index++ {
-		c := runes[index]
-		if escaped {
-			b.WriteRune(' ')
-			escaped = false
-			continue
-		}
-		if c == '`' {
-			b.WriteRune(' ')
-			escaped = true
-			continue
-		}
-		if quote != 0 {
-			b.WriteRune(' ')
-			if c == quote {
-				// PowerShell escapes a single quote inside a single-quoted
-				// string by doubling it.
-				if quote == '\'' && index+1 < len(runes) && runes[index+1] == '\'' {
-					index++
-					b.WriteRune(' ')
-					continue
-				}
-				quote = 0
-			}
-			continue
-		}
-		if c == '\'' || c == '"' {
-			quote = c
-			b.WriteRune(' ')
-			continue
-		}
-		b.WriteRune(c)
-	}
-	return b.String()
-}
-
 // stripDoubleQuotedSpans replaces the contents of every double-quoted span
 // (quotes included) with spaces, preserving the string's length and the
 // position of unquoted text. cmd.exe treats a double-quoted span as a single
@@ -535,15 +256,7 @@ func stripCmdCaretEscapes(command string) string {
 // quoted-text false positives the preflight command-position check exists to
 // avoid, just after execution instead of before it.
 func detectShellOutputIssue(output string, goos string) *shellIssue {
-	shell := shellRuntime{GOOS: goos, Executable: "/bin/sh", Syntax: "/bin/sh", Kind: shellKindPOSIX}
-	if goos == "windows" {
-		shell = shellRuntime{GOOS: goos, Executable: "cmd.exe", Syntax: "Windows cmd.exe", Kind: shellKindCmd}
-	}
-	return detectShellOutputIssueForRuntime(output, shell)
-}
-
-func detectShellOutputIssueForRuntime(output string, shell shellRuntime) *shellIssue {
-	if shell.GOOS != "windows" {
+	if goos != "windows" {
 		return nil
 	}
 	lower := strings.ToLower(output)
@@ -553,8 +266,8 @@ func detectShellOutputIssueForRuntime(output string, shell shellRuntime) *shellI
 	if wslServiceDeniedInOutput(lower) {
 		return windowsMsysSandboxIssue("WSL bash could not connect to the WSL service under Zero's Windows sandbox (Bash/Service/CreateInstance/E_ACCESSDENIED).")
 	}
-	if shell.Kind == shellKindCmd && (strings.Contains(lower, "the syntax of the command is incorrect") ||
-		strings.Contains(lower, "is not recognized as an internal or external command")) {
+	if strings.Contains(lower, "the syntax of the command is incorrect") ||
+		strings.Contains(lower, "is not recognized as an internal or external command") {
 		return &shellIssue{
 			Kind:       "windows_shell_syntax",
 			Message:    "Windows cmd.exe rejected the command syntax.",

internal/tools/shell_runtime_test.go

@@ -1,218 +1,10 @@
 package tools
 
 import (
-	"errors"
-	"os/exec"
-	"runtime"
 	"strings"
 	"testing"
 )
 
-func TestDetectShellRuntimePrefersPowerShellSevenOnWindows(t *testing.T) {
-	lookPath := func(name string) (string, error) {
-		if name == "pwsh.exe" {
-			return `C:\Program Files\PowerShell\7\pwsh.exe`, nil
-		}
-		return "", errors.New("not found")
-	}
-	shell := detectShellRuntimeWithLookup("windows", lookPath, func(string) string { return "" })
-	if shell.Kind != shellKindPowerShell || !strings.HasSuffix(strings.ToLower(shell.Executable), `\pwsh.exe`) {
-		t.Fatalf("shell = %#v, want PowerShell 7", shell)
-	}
-}
-
-func TestDetectShellRuntimeFallsBackThroughWindowsPowerShellToCmd(t *testing.T) {
-	t.Run("windows powershell", func(t *testing.T) {
-		lookPath := func(name string) (string, error) {
-			if name == "powershell.exe" {
-				return `C:\Windows\System32\WindowsPowerShell\v1.0\powershell.exe`, nil
-			}
-			return "", errors.New("not found")
-		}
-		shell := detectShellRuntimeWithLookup("windows", lookPath, func(string) string { return "" })
-		if shell.Kind != shellKindPowerShell || !strings.HasSuffix(strings.ToLower(shell.Executable), `\powershell.exe`) {
-			t.Fatalf("shell = %#v, want Windows PowerShell", shell)
-		}
-	})
-
-	t.Run("cmd", func(t *testing.T) {
-		shell := detectShellRuntimeWithLookup(
-			"windows",
-			func(string) (string, error) { return "", errors.New("not found") },
-			func(string) string { return "" },
-		)
-		if shell.Kind != shellKindCmd || shell.Executable != "cmd.exe" {
-			t.Fatalf("shell = %#v, want cmd.exe fallback", shell)
-		}
-	})
-}
-
-func TestDetectShellRuntimeSkipsUnusablePowerShell(t *testing.T) {
-	lookPath := func(name string) (string, error) {
-		switch name {
-		case "pwsh.exe":
-			return `C:\broken\pwsh.exe`, nil
-		case "powershell.exe":
-			return `C:\Windows\System32\WindowsPowerShell\v1.0\powershell.exe`, nil
-		default:
-			return "", errors.New("not found")
-		}
-	}
-	shell := detectShellRuntimeWithProbe(
-		"windows",
-		lookPath,
-		func(string) string { return "" },
-		func(path string) bool { return !strings.Contains(path, `\broken\`) },
-	)
-	if shell.Kind != shellKindPowerShell || strings.Contains(shell.Executable, `\broken\`) {
-		t.Fatalf("shell = %#v, want usable Windows PowerShell fallback", shell)
-	}
-}
-
-func TestPowerShellArgumentsDisableProfilesAndRequestUTF8(t *testing.T) {
-	shell := shellRuntime{GOOS: "windows", Executable: "pwsh.exe", Syntax: "PowerShell", Kind: shellKindPowerShell}
-	args := shell.arguments("Write-Output 'hello'")
-	joined := strings.Join(args, "\n")
-	for _, want := range []string{
-		"-NoLogo",
-		"-NoProfile",
-		"-Command",
-		windowsPowerShellUTF8Prefix,
-		"$ErrorActionPreference = 'Stop'",
-		"Write-Output 'hello'",
-		"exit $LASTEXITCODE",
-	} {
-		if !strings.Contains(joined, want) {
-			t.Fatalf("PowerShell args missing %q: %#v", want, args)
-		}
-	}
-	script := args[len(args)-1]
-	preferenceIndex := strings.Index(script, "$ErrorActionPreference")
-	commandIndex := strings.Index(script, "Write-Output 'hello'")
-	exitIndex := strings.Index(script, "exit $LASTEXITCODE")
-	if preferenceIndex < 0 || commandIndex <= preferenceIndex || exitIndex <= commandIndex {
-		t.Fatalf("PowerShell failure handling is not ordered around the command: %q", script)
-	}
-}
-
-func TestWindowsPowerShellArgumentsPropagateFailures(t *testing.T) {
-	if runtime.GOOS != "windows" {
-		t.Skip("Windows PowerShell integration test")
-	}
-	executable, err := exec.LookPath("powershell.exe")
-	if err != nil {
-		t.Skipf("Windows PowerShell unavailable: %v", err)
-	}
-	shell := shellRuntime{
-		GOOS:       "windows",
-		Executable: executable,
-		Syntax:     "PowerShell",
-		Kind:       shellKindPowerShell,
-	}
-
-	t.Run("native exit code after cmdlet", func(t *testing.T) {
-		command := exec.Command(executable, shell.arguments("cmd /c exit 5; Write-Output done")...)
-		output, err := command.CombinedOutput()
-		var exitErr *exec.ExitError
-		if !errors.As(err, &exitErr) || exitErr.ExitCode() != 5 {
-			t.Fatalf("exit = %v, output = %q; want exact native exit code 5", err, output)
-		}
-		if !strings.Contains(string(output), "done") {
-			t.Fatalf("output = %q, want command output before propagated failure", output)
-		}
-	})
-
-	t.Run("cmdlet error stops script", func(t *testing.T) {
-		missing := strings.ReplaceAll(t.TempDir()+`\missing`, `'`, `''`)
-		commandText := "Get-Item -LiteralPath '" + missing + "'; Write-Output after"
-		command := exec.Command(executable, shell.arguments(commandText)...)
-		output, err := command.CombinedOutput()
-		if err == nil {
-			t.Fatalf("cmdlet failure reported success: %q", output)
-		}
-		if strings.Contains(string(output), "after") {
-			t.Fatalf("script continued after cmdlet failure: %q", output)
-		}
-	})
-}
-
-func TestWindowsPowerShellGuidanceAvoidsUnsupportedChainOperators(t *testing.T) {
-	shell := shellRuntime{
-		GOOS:       "windows",
-		Executable: `C:\Windows\System32\WindowsPowerShell\v1.0\powershell.exe`,
-		Syntax:     "PowerShell",
-		Kind:       shellKindPowerShell,
-	}
-	for _, guidance := range []string{
-		shellGuidanceForRuntime(shell),
-		hostShellEnvironmentGuidanceForRuntime(shell),
-	} {
-		for _, want := range []string{"Windows PowerShell 5.1", "&&", "||", "if ($?)"} {
-			if !strings.Contains(guidance, want) {
-				t.Fatalf("legacy PowerShell guidance missing %q: %q", want, guidance)
-			}
-		}
-	}
-}
-
-func TestWindowsPowerShellCommandIssueFlagsUnsupportedChainOperators(t *testing.T) {
-	legacy := shellRuntime{
-		GOOS:       "windows",
-		Executable: "powershell.exe",
-		Syntax:     "PowerShell",
-		Kind:       shellKindPowerShell,
-	}
-	for _, command := range []string{
-		"Write-Output one && Write-Output two",
-		"Write-Output one || Write-Output two",
-	} {
-		issue := detectShellCommandIssueForRuntime(command, legacy)
-		if issue == nil || issue.Kind != "windows_powershell_version" {
-			t.Fatalf("legacy PowerShell command %q issue = %#v, want version issue", command, issue)
-		}
-	}
-	for _, command := range []string{
-		`Write-Output "one && two"`,
-		"Write-Output 'one || two'",
-		"Write-Output one `&`& Write-Output two",
-	} {
-		if issue := detectShellCommandIssueForRuntime(command, legacy); issue != nil {
-			t.Fatalf("literal legacy PowerShell operators in %q produced issue %#v", command, issue)
-		}
-	}
-
-	modern := shellRuntime{GOOS: "windows", Executable: "pwsh.exe", Syntax: "PowerShell", Kind: shellKindPowerShell}
-	if issue := detectShellCommandIssueForRuntime("Write-Output one && Write-Output two", modern); issue != nil {
-		t.Fatalf("PowerShell 7 chain operator produced issue %#v", issue)
-	}
-}
-
-func TestPowerShellCommandIssueAllowsAliasesAndBlocksMsysExecutables(t *testing.T) {
-	shell := shellRuntime{GOOS: "windows", Executable: "pwsh.exe", Syntax: "PowerShell", Kind: shellKindPowerShell}
-	for _, command := range []string{
-		`ls -Force`,
-		`cat README.md`,
-		`Get-ChildItem | Select-Object -First 10`,
-		`Write-Output 'grep README.md; head file.txt'`,
-		`Write-Output 'cd /tmp'`,
-	} {
-		if issue := detectShellCommandIssueForRuntime(command, shell); issue != nil {
-			t.Fatalf("PowerShell-native command %q was blocked: %#v", command, issue)
-		}
-	}
-	for _, command := range []string{
-		`grep README.md`,
-		`Get-Content README.md | head -10`,
-		`cat.exe README.md`,
-		`bash -lc "make test"`,
-		`Write-Output ok; sed -n '1,5p' README.md`,
-	} {
-		if issue := detectShellCommandIssueForRuntime(command, shell); issue == nil || issue.Kind != windowsMsysSandboxKind {
-			t.Fatalf("MSYS-prone command %q was not blocked: %#v", command, issue)
-		}
-	}
-}
-
 func TestDetectShellCommandIssueFlagsMsysBinaryPaths(t *testing.T) {
 	for _, command := range []string{
 		`for /F %i in ('whoami') do echo %i | "C:\Program Files\Git\usr\bin\head.exe" -1`,

internal/tui/clipboard.go

@@ -23,12 +23,16 @@ type clipboardImageMsg struct {
 	err       error
 }
 
+// readClipboardImage is the OS clipboard image reader. A var so tests can
+// substitute a stub instead of depending on the developer's real clipboard.
+var readClipboardImage = imageinput.ReadClipboardImage
+
 // readClipboardImageCmd reads the OS clipboard for image content off the
 // Update goroutine. Returns a clipboardImageMsg with the bytes, or nil (no
 // command) if there is no image — the caller treats nil as a silent no-op.
 func readClipboardImageCmd() tea.Cmd {
 	return func() tea.Msg {
-		data, mediaType, err := imageinput.ReadClipboardImage()
+		data, mediaType, err := readClipboardImage()
 		if err != nil {
 			return clipboardImageMsg{err: err}
 		}

internal/tui/command_bash.go

@@ -2,11 +2,12 @@ package tui
 
 import (
 	"context"
+	"os/exec"
+	"runtime"
 	"strings"
 	"time"
 
 	tea "charm.land/bubbletea/v2"
-	"github.com/Gitlawb/zero/internal/tools"
 )
 
 // bashEscapeTimeout bounds a "!cmd" shell escape so a hung command can't freeze
@@ -29,7 +30,8 @@ func runBashEscape(cwd, command string) tea.Cmd {
 		ctx, cancel := context.WithTimeout(context.Background(), bashEscapeTimeout)
 		defer cancel()
 
-		cmd := tools.NewHostShellCommandContext(ctx, command)
+		name, shellArgs := escapeShell(command)
+		cmd := exec.CommandContext(ctx, name, shellArgs...)
 		if strings.TrimSpace(cwd) != "" {
 			cmd.Dir = cwd
 		}
@@ -49,11 +51,15 @@ func runBashEscape(cwd, command string) tea.Cmd {
 	}
 }
 
-// escapeShell returns the platform shell and arguments for tests and display.
-// Execution itself uses tools.NewHostShellCommandContext so the cmd.exe
-// fallback receives its required raw Windows command line.
+// escapeShell returns the platform shell and arguments for a "!cmd" escape,
+// matching the agent bash tool: cmd.exe on Windows, /bin/sh elsewhere. Hardcoding
+// "bash" broke the escape on stock Windows (no bash on PATH) and anywhere bash is
+// not installed at a predictable path.
 func escapeShell(command string) (string, []string) {
-	return tools.HostShellCommand(command)
+	if runtime.GOOS == "windows" {
+		return "cmd.exe", []string{"/d", "/s", "/c", command}
+	}
+	return "/bin/sh", []string{"-c", command}
 }
 
 func appendNote(text, note string) string {

internal/tui/composer_test.go

@@ -6,6 +6,8 @@ import (
 	"testing"
 
 	tea "charm.land/bubbletea/v2"
+
+	"github.com/Gitlawb/zero/internal/imageinput"
 )
 
 func TestComposerInsertNewlineAtCursor(t *testing.T) {
@@ -129,22 +131,77 @@ func TestSanitizeComposerPastePreservesNewlines(t *testing.T) {
 	}
 }
 
-func TestCtrlVDoesNotPasteIntoComposer(t *testing.T) {
+// Ctrl+V must never insert TEXT: bracketed paste is the only text path, so
+// letting Bubble's own Ctrl+V binding also read the clipboard would double-paste.
+// It may return a command, but that command is the image probe below, never a
+// text paste, so the composer contents are unchanged either way.
+func TestCtrlVDoesNotPasteTextIntoComposer(t *testing.T) {
 	m := newModel(context.Background(), Options{})
 	m.input.SetValue("hello")
 	m.input.CursorEnd()
 
-	updated, cmd := m.Update(testKeyCtrl('v'))
+	updated, _ := m.Update(testKeyCtrl('v'))
 	next := updated.(model)
 
-	if cmd != nil {
-		t.Fatal("ctrl+v should not run the textinput clipboard paste command")
-	}
 	if got := next.composerValue(); got != "hello" {
 		t.Fatalf("composer value after ctrl+v = %q, want unchanged", got)
 	}
 }
 
+// Ctrl+V probes the clipboard for an image (#534). A clipboard holding a
+// screenshot produces no bracketed paste at all, so without this the empty-paste
+// image probe in routePaste never runs and Ctrl+V does nothing, which is exactly
+// what users reported: right-click paste attached the image, Ctrl+V did not.
+func TestCtrlVProbesClipboardForImage(t *testing.T) {
+	// Stubbed BEFORE Update, so the command Update returns is the one that runs.
+	// Asserting only that some command came back, then running a freshly built
+	// probe, would pass even if the key never reached the image route at all.
+	original := readClipboardImage
+	t.Cleanup(func() { readClipboardImage = original })
+	readClipboardImage = func() ([]byte, string, error) {
+		return []byte("png-bytes"), "image/png", nil
+	}
+
+	// Both modifiers: macOS reports Command as ModSuper, so a handler matching
+	// only ModCtrl leaves Cmd+V doing nothing on the platform where screenshots
+	// are most often on the clipboard.
+	for name, key := range map[string]tea.KeyPressMsg{
+		"ctrl+v": testKeyCtrl('v'),
+		"cmd+v":  testKeyPressMod('v', tea.ModSuper),
+	} {
+		t.Run(name, func(t *testing.T) {
+			m := newModel(context.Background(), Options{})
+			_, cmd := m.Update(key)
+			if cmd == nil {
+				t.Fatal("no command issued; the clipboard image probe never ran")
+			}
+			image, ok := execCmd(cmd).(clipboardImageMsg)
+			if !ok {
+				t.Fatal("the command issued was not the clipboard image probe")
+			}
+			if string(image.data) != "png-bytes" || image.mediaType != "image/png" {
+				t.Fatalf("unexpected image message: %+v", image)
+			}
+		})
+	}
+}
+
+// With no image on the clipboard the probe stays silent: Ctrl+V while copying
+// text must not emit a notice or disturb the composer. Driven through Update
+// rather than by calling the probe directly, so this covers the real key route
+// and not just the command in isolation.
+func TestClipboardImageProbeSilentWithoutImage(t *testing.T) {
+	original := readClipboardImage
+	t.Cleanup(func() { readClipboardImage = original })
+	readClipboardImage = func() ([]byte, string, error) { return nil, "", nil }
+
+	m := newModel(context.Background(), Options{})
+	_, cmd := m.Update(testKeyCtrl('v'))
+	if msg := execCmd(cmd); msg != nil {
+		t.Fatalf("probe emitted %T with no image on the clipboard, want no message", msg)
+	}
+}
+
 func TestPastedMultilineComposerContentRendersAsPreview(t *testing.T) {
 	paste := strings.Join([]string{
 		"Create a book library dashboard page with the Bootstrap theme.",
@@ -465,3 +522,53 @@ func TestComposerTerminalWordKeybindings(t *testing.T) {
 		})
 	}
 }
+
+// A clipboard that holds an image the host cannot extract must say so. This is
+// the macOS case: neither pngpaste nor PyObjC ships with the OS, so the reader
+// fails on a stock Mac, and reporting that as "no image" meant Ctrl+V did
+// nothing at all with no explanation. Silence is the wrong answer to a
+// condition the user can act on.
+func TestClipboardImageUnreadableSurfacesToUser(t *testing.T) {
+	original := readClipboardImage
+	t.Cleanup(func() { readClipboardImage = original })
+	readClipboardImage = func() ([]byte, string, error) {
+		return nil, "", imageinput.ErrClipboardImageUnreadable
+	}
+
+	m := newModel(context.Background(), Options{})
+	_, cmd := m.Update(testKeyCtrl('v'))
+	if cmd == nil {
+		t.Fatal("no command issued; the clipboard image probe never ran")
+	}
+	msg := execCmd(cmd)
+	image, ok := msg.(clipboardImageMsg)
+	if !ok {
+		t.Fatalf("probe returned %T, want clipboardImageMsg carrying the failure", msg)
+	}
+	if image.err == nil {
+		t.Fatal("the unreadable-clipboard failure was swallowed; the user is told nothing")
+	}
+	// The message has to name the remedy, since the whole point is that the user
+	// can fix this by installing something.
+	if !strings.Contains(image.err.Error(), "pngpaste") {
+		t.Fatalf("error = %q, want it to name what to install", image.err.Error())
+	}
+
+	// And it must reach the transcript as an error row rather than stopping at
+	// the message, which is where the old silent no-op ended.
+	updated, _ := m.Update(image)
+	next, ok := updated.(model)
+	if !ok {
+		t.Fatalf("Update returned %T, want model", updated)
+	}
+	found := false
+	for _, row := range next.transcript {
+		if row.kind == rowError && strings.Contains(row.text, "Clipboard image read failed") {
+			found = true
+			break
+		}
+	}
+	if !found {
+		t.Fatal("the failure never reached the transcript; the user still sees nothing")
+	}
+}

internal/tui/input_compat.go

@@ -34,6 +34,14 @@ func keyCtrl(msg tea.KeyMsg, code rune) bool {
 	return keyCode(msg) == code && keyHasMod(msg, tea.ModCtrl)
 }
 
+// keySuper matches the Command key on macOS, which the rest of the TUI models as
+// ModSuper (see keybindings.go). Kept separate from keyCtrl because a binding
+// that means Ctrl on Linux and Windows usually means Command on macOS, and the
+// two arrive as different modifiers.
+func keySuper(msg tea.KeyMsg, code rune) bool {
+	return keyCode(msg) == code && keyHasMod(msg, tea.ModSuper)
+}
+
 func keyCtrlArrow(msg tea.KeyMsg, code rune) bool {
 	return keyIs(msg, code) && keyHasMod(msg, tea.ModCtrl)
 }

internal/tui/model.go

@@ -1699,6 +1699,27 @@ func (m model) updateModel(msg tea.Msg) (tea.Model, tea.Cmd) {
 				m.input.SetWidth(maxInt(20, m.chatColumnWidth()-14))
 				return m, nil
 			}
+		case keyCtrl(msg, 'v'), keySuper(msg, 'v'):
+			// Ctrl+V probes the clipboard for an IMAGE only. Text pasting stays
+			// exclusively on the terminal's bracketed-paste path (Bubble's own
+			// Ctrl+V binding is disabled in newModel for exactly that reason), so
+			// this cannot double-insert text. It is needed because a clipboard
+			// holding a screenshot produces no bracketed paste at all: the terminal
+			// has no text to send, so routePaste never runs and its empty-content
+			// image probe never fires. Right-click paste reached that probe only
+			// because it always delivers a clipboardReadMsg, empty or not.
+			// readClipboardImageCmd yields no message when the clipboard holds no
+			// image, so Ctrl+V with text on the clipboard stays a no-op here and is
+			// handled by the bracketed paste exactly as before.
+			//
+			// Cmd+V is matched too, since macOS reports Command as ModSuper rather
+			// than ModCtrl. That only helps on terminals that deliver the key to the
+			// application: one that handles Cmd+V itself pastes the clipboard TEXT
+			// and sends no key event, so an image-only clipboard still produces
+			// nothing for this to react to.
+			if m.noBlockingModal() {
+				return m, readClipboardImageCmd()
+			}
 		case keyCtrl(msg, 'f'):
 			if m.picker != nil && m.picker.kind == pickerModel {
 				if m.modelPickerIsLoading() {

internal/tui/tui_fixes_test.go

@@ -42,19 +42,19 @@ func TestBashEscapeGatedByPermissionMode(t *testing.T) {
 	}
 }
 
-// The "!" escape must use the same detected host shell as the agent tools.
+// The "!" escape must use the platform shell (cmd.exe on Windows, /bin/sh
+// elsewhere), not a hardcoded "bash" that is absent on stock Windows.
 func TestEscapeShellWrapsCommandForPlatform(t *testing.T) {
 	name, args := escapeShell("echo hi")
 	if name == "" {
 		t.Fatal("escapeShell returned an empty executable")
 	}
-	if len(args) == 0 || !strings.Contains(args[len(args)-1], "echo hi") {
-		t.Fatalf("escapeShell args = %v, want the command in the final arg", args)
+	if len(args) == 0 || args[len(args)-1] != "echo hi" {
+		t.Fatalf("escapeShell args = %v, want the command as the final arg", args)
 	}
 	if runtime.GOOS == "windows" {
-		lowerName := strings.ToLower(filepath.Base(name))
-		if lowerName != "pwsh.exe" && lowerName != "powershell.exe" && lowerName != "cmd.exe" {
-			t.Fatalf("windows shell = %q %v, want PowerShell or cmd.exe fallback", name, args)
+		if name != "cmd.exe" || args[0] != "/d" {
+			t.Fatalf("windows shell = %q %v, want cmd.exe /d /s /c", name, args)
 		}
 	} else if name != "/bin/sh" || args[0] != "-c" {
 		t.Fatalf("unix shell = %q %v, want /bin/sh -c", name, args)

scripts/sandbox-smoke.sh

@@ -52,7 +52,7 @@ case "$(go env GOOS)" in
     ZERO_SANDBOX_REAL_SMOKE=1 \
       ZERO_WINDOWS_COMMAND_RUNNER_EXE="$tmpdir/windows-zero-windows-command-runner.exe" \
       ZERO_WINDOWS_SANDBOX_SETUP_EXE="$tmpdir/windows-zero-windows-sandbox-setup.exe" \
-      go test ./internal/sandbox -run 'TestWindowsRestrictedTokenRealSandboxSmoke|TestWindowsRestrictedTokenPowerShell' -count=1
+      go test ./internal/sandbox -run TestWindowsRestrictedTokenRealSandboxSmoke -count=1
     ;;
   *)
     echo "No real sandbox smoke is defined for this host platform."