diff --git a/cli/cmd/serve.go b/cli/cmd/serve.go
index e40d57b1e0..e8f48eb5b4 100644
--- a/cli/cmd/serve.go
+++ b/cli/cmd/serve.go
@@ -100,6 +100,9 @@ environment variable (the --host-key flag takes precedence).`,
   onyx-cli serve --host 0.0.0.0 --port 2222
   onyx-cli serve --idle-timeout 30m --max-session-timeout 2h`,
 		RunE: func(cmd *cobra.Command, args []string) error {
+			// Sessions here belong to remote clients; keep them off the host filesystem.
+			tui.RemoteMode = true
+
 			serverCfg := config.Load()
 			if serverCfg.ServerURL == "" {
 				return exitcodes.New(exitcodes.NotConfigured, "server URL is not configured\n  Run: onyx-cli chat to complete first-time setup")
diff --git a/cli/internal/tui/commands.go b/cli/internal/tui/commands.go
index ed026654dc..ce64c1242c 100644
--- a/cli/internal/tui/commands.go
+++ b/cli/internal/tui/commands.go
@@ -267,6 +267,10 @@ func cmdSelectModel(m Model, idxStr string) (Model, tea.Cmd) {
 }
 
 func cmdAttach(m Model, pathStr string) (Model, tea.Cmd) {
+	if RemoteMode {
+		m.viewport.addWarning("/attach is disabled over SSH: paths resolve on the server host, not yours.")
+		return m, nil
+	}
 	if pathStr == "" {
 		m.viewport.addWarning("Usage: /attach <file_path>")
 		return m, nil
diff --git a/cli/internal/tui/commands_test.go b/cli/internal/tui/commands_test.go
index 7c880765a8..4893b17619 100644
--- a/cli/internal/tui/commands_test.go
+++ b/cli/internal/tui/commands_test.go
@@ -1,6 +1,8 @@
 package tui
 
 import (
+	"os"
+	"path/filepath"
 	"strings"
 	"testing"
 
@@ -279,6 +281,43 @@ func TestSelectAgentFromPickerUsesIDWhenNameMatches(t *testing.T) {
 	}
 }
 
+func TestAttachRefusedInRemoteMode(t *testing.T) {
+	RemoteMode = true
+	t.Cleanup(func() { RemoteMode = false })
+
+	m := NewModel(config.DefaultConfig(), nil)
+	m, cmd := cmdAttach(m, "/etc/passwd")
+
+	if cmd != nil {
+		t.Fatal("expected no upload command in remote mode")
+	}
+	if len(m.viewport.entries) == 0 {
+		t.Fatal("expected a warning entry")
+	}
+	got := m.viewport.entries[len(m.viewport.entries)-1].content
+	if !strings.Contains(got, "disabled over SSH") {
+		t.Errorf("warning = %q, want a refusal mentioning SSH", got)
+	}
+}
+
+func TestDetectFileDropIgnoredInRemoteMode(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "secret.txt")
+	if err := os.WriteFile(path, []byte("secret"), 0o600); err != nil {
+		t.Fatalf("write temp file: %v", err)
+	}
+
+	if got := detectFileDrop(path); got != path {
+		t.Fatalf("local detectFileDrop = %q, want %q", got, path)
+	}
+
+	RemoteMode = true
+	t.Cleanup(func() { RemoteMode = false })
+
+	if got := detectFileDrop(path); got != "" {
+		t.Errorf("remote detectFileDrop = %q, want no match", got)
+	}
+}
+
 func TestSelectModelInvalidIndex(t *testing.T) {
 	m := NewModel(config.DefaultConfig(), nil)
 	m, _ = cmdSelectModel(m, "5")
diff --git a/cli/internal/tui/input.go b/cli/internal/tui/input.go
index 6496542c8a..5dbd7863ad 100644
--- a/cli/internal/tui/input.go
+++ b/cli/internal/tui/input.go
@@ -204,8 +204,12 @@ type fileDropMsg struct {
 	path string
 }
 
-// detectFileDrop checks if the text looks like a file path.
+// detectFileDrop checks if the text looks like a file path. It never matches
+// in remote mode, where the path would resolve on the server host.
 func detectFileDrop(text string) string {
+	if RemoteMode {
+		return ""
+	}
 	cleaned := strings.Trim(text, "'\"")
 	if cleaned == "" {
 		return ""
diff --git a/cli/internal/tui/sshauth.go b/cli/internal/tui/sshauth.go
index 402ed2b8c6..0a51a84c7c 100644
--- a/cli/internal/tui/sshauth.go
+++ b/cli/internal/tui/sshauth.go
@@ -14,6 +14,11 @@ const (
 	MaxAPIKeyRetries = 5
 )
 
+// RemoteMode marks this process as serving the TUI to remote clients.
+// Commands that touch the host filesystem are refused while it is set,
+// because those paths resolve on the operator's machine, not the client's.
+var RemoteMode bool
+
 // --- auth prompt (bubbletea model) ---
 
 type authState int