diff --git a/backend/internal/session_manager/manager.go b/backend/internal/session_manager/manager.go
index 39e591614..bb7a6ff2a 100644
--- a/backend/internal/session_manager/manager.go
+++ b/backend/internal/session_manager/manager.go
@@ -1427,18 +1427,39 @@ func restoreArgv(ctx context.Context, agent ports.Agent, id domain.SessionID, wo
 // lookPath (exec.LookPath in prod) before any runtime work happens. Adapters
 // that can't resolve their binary now return ports.ErrAgentBinaryNotFound from
 // GetLaunchCommand directly; this guard is a defense-in-depth for adapters
-// that return an argv[0] like "claude" without verifying.
+// that return an argv[0] like "claude" without verifying. Some adapters prefix
+// their command with `env KEY=value`; in that case validate the first real
+// executable after the environment assignments.
 func (m *Manager) validateAgentBinary(argv []string) error {
 	if len(argv) == 0 {
 		return fmt.Errorf("agent: empty launch argv: %w", ports.ErrAgentBinaryNotFound)
 	}
-	bin := argv[0]
+	bin, ok := launchBinary(argv)
+	if !ok {
+		return fmt.Errorf("agent: launch argv missing binary: %w", ports.ErrAgentBinaryNotFound)
+	}
 	if _, err := m.lookPath(bin); err != nil {
 		return fmt.Errorf("agent binary %q: %w", bin, ports.ErrAgentBinaryNotFound)
 	}
 	return nil
 }
 
+func launchBinary(argv []string) (string, bool) {
+	if len(argv) == 0 {
+		return "", false
+	}
+	if filepath.Base(argv[0]) != "env" {
+		return argv[0], true
+	}
+	for _, arg := range argv[1:] {
+		if strings.Contains(arg, "=") {
+			continue
+		}
+		return arg, true
+	}
+	return "", false
+}
+
 func (m *Manager) validateRuntimePrerequisites() error {
 	if runtime.GOOS == "windows" {
 		return nil
diff --git a/backend/internal/session_manager/manager_test.go b/backend/internal/session_manager/manager_test.go
index 3685b9be7..2ccaaea2b 100644
--- a/backend/internal/session_manager/manager_test.go
+++ b/backend/internal/session_manager/manager_test.go
@@ -8,6 +8,7 @@ import (
 	"log/slog"
 	"os"
 	"path/filepath"
+	"reflect"
 	"runtime"
 	"strings"
 	"testing"
@@ -202,6 +203,15 @@ func (fakeAgent) SessionInfo(context.Context, ports.SessionRef) (ports.SessionIn
 	return ports.SessionInfo{}, false, nil
 }
 
+type launchArgvAgent struct {
+	fakeAgent
+	argv []string
+}
+
+func (a launchArgvAgent) GetLaunchCommand(context.Context, ports.LaunchConfig) ([]string, error) {
+	return a.argv, nil
+}
+
 // fakeAgents resolves every harness to the same fakeAgent.
 type fakeAgents struct{}
 
@@ -1452,6 +1462,103 @@ func TestSpawn_RejectsMissingAgentBinary(t *testing.T) {
 	requireNoPromptDir(t, dataDir, "mer-1")
 }
 
+func TestSpawn_ValidatesBinaryAfterEnvPrefix(t *testing.T) {
+	st := newFakeStore()
+	st.projects["mer"] = domain.ProjectRecord{ID: "mer", Config: testRoleAgents()}
+	rt := &fakeRuntime{}
+	ws := &fakeWorkspace{}
+	lookedUp := []string{}
+	lookPath := func(name string) (string, error) {
+		lookedUp = append(lookedUp, name)
+		switch name {
+		case "tmux":
+			return "/bin/tmux", nil
+		case "opencode":
+			return "/usr/local/bin/opencode", nil
+		default:
+			return "", fmt.Errorf("exec: %q: not found", name)
+		}
+	}
+	agent := launchArgvAgent{argv: []string{"env", "OPENCODE_CONFIG=/tmp/ao/opencode.json", "opencode", "--agent", "ao-mer-1"}}
+	m := New(Deps{Runtime: rt, Agents: singleAgent{agent: agent}, Workspace: ws, Store: st, Messenger: &fakeMessenger{}, Lifecycle: &fakeLCM{store: st}, LookPath: lookPath})
+
+	if _, err := m.Spawn(ctx, ports.SpawnConfig{ProjectID: "mer", Kind: domain.KindWorker}); err != nil {
+		t.Fatalf("Spawn: %v", err)
+	}
+	if !reflect.DeepEqual(lookedUp, []string{"tmux", "opencode"}) {
+		t.Fatalf("lookups = %#v, want tmux then opencode", lookedUp)
+	}
+	if rt.created != 1 {
+		t.Fatalf("runtime.Create calls = %d, want 1", rt.created)
+	}
+	if !reflect.DeepEqual(rt.lastCfg.Argv, agent.argv) {
+		t.Fatalf("runtime argv = %#v, want original argv %#v", rt.lastCfg.Argv, agent.argv)
+	}
+}
+
+func TestSpawn_RejectsMissingBinaryAfterEnvPrefix(t *testing.T) {
+	st := newFakeStore()
+	st.projects["mer"] = domain.ProjectRecord{ID: "mer", Config: testRoleAgents()}
+	rt := &fakeRuntime{}
+	ws := &fakeWorkspace{}
+	lookedUp := []string{}
+	lookPath := func(name string) (string, error) {
+		lookedUp = append(lookedUp, name)
+		if name == "tmux" {
+			return "/bin/tmux", nil
+		}
+		return "", fmt.Errorf("exec: %q: not found", name)
+	}
+	agent := launchArgvAgent{argv: []string{"env", "OPENCODE_CONFIG=/tmp/ao/opencode.json", "opencode", "--agent", "ao-mer-1"}}
+	m := New(Deps{Runtime: rt, Agents: singleAgent{agent: agent}, Workspace: ws, Store: st, Messenger: &fakeMessenger{}, Lifecycle: &fakeLCM{store: st}, LookPath: lookPath})
+
+	_, err := m.Spawn(ctx, ports.SpawnConfig{ProjectID: "mer", Kind: domain.KindWorker})
+	if !errors.Is(err, ports.ErrAgentBinaryNotFound) {
+		t.Fatalf("err = %v, want ports.ErrAgentBinaryNotFound", err)
+	}
+	if !reflect.DeepEqual(lookedUp, []string{"tmux", "opencode"}) {
+		t.Fatalf("lookups = %#v, want tmux then opencode", lookedUp)
+	}
+	if rt.created != 0 {
+		t.Fatal("runtime.Create must NOT run when the env-prefixed agent binary is missing")
+	}
+	if ws.destroyed != 1 {
+		t.Fatal("workspace must be torn down when the pre-launch binary check fails")
+	}
+	if rec, present := st.sessions["mer-1"]; present {
+		t.Fatalf("seed row must be deleted before a runtime handle is live, got %+v", rec)
+	}
+}
+
+func TestSpawn_RejectsEnvPrefixWithoutBinary(t *testing.T) {
+	st := newFakeStore()
+	st.projects["mer"] = domain.ProjectRecord{ID: "mer", Config: testRoleAgents()}
+	rt := &fakeRuntime{}
+	ws := &fakeWorkspace{}
+	agent := launchArgvAgent{argv: []string{"env", "OPENCODE_CONFIG=/tmp/ao/opencode.json"}}
+	m := New(Deps{
+		Runtime: rt, Agents: singleAgent{agent: agent}, Workspace: ws, Store: st,
+		Messenger: &fakeMessenger{}, Lifecycle: &fakeLCM{store: st},
+		LookPath: func(name string) (string, error) {
+			if name == "tmux" {
+				return "/bin/tmux", nil
+			}
+			return "/bin/" + name, nil
+		},
+	})
+
+	_, err := m.Spawn(ctx, ports.SpawnConfig{ProjectID: "mer", Kind: domain.KindWorker})
+	if !errors.Is(err, ports.ErrAgentBinaryNotFound) {
+		t.Fatalf("err = %v, want ports.ErrAgentBinaryNotFound", err)
+	}
+	if rt.created != 0 {
+		t.Fatal("runtime.Create must NOT run when env-prefixed argv has no binary")
+	}
+	if ws.destroyed != 1 {
+		t.Fatal("workspace must be torn down when env-prefixed argv has no binary")
+	}
+}
+
 func TestSpawn_RejectsMissingTmuxBeforeSessionRow(t *testing.T) {
 	if runtime.GOOS == "windows" {
 		t.Skip("Windows uses ConPTY, not tmux")