diff --git a/backend/internal/adapters/runtime/tmux/tmux.go b/backend/internal/adapters/runtime/tmux/tmux.go
index 5fbbafb25..ba7524ed8 100644
--- a/backend/internal/adapters/runtime/tmux/tmux.go
+++ b/backend/internal/adapters/runtime/tmux/tmux.go
@@ -3,6 +3,8 @@ package tmux
 
 import (
 	"context"
+	"crypto/sha256"
+	"encoding/hex"
 	"errors"
 	"fmt"
 	"os"
@@ -12,6 +14,7 @@ import (
 	"strings"
 	"time"
 
+	"github.com/aoagents/agent-orchestrator/backend/internal/domain"
 	"github.com/aoagents/agent-orchestrator/backend/internal/ports"
 )
 
@@ -61,14 +64,14 @@ func New(opts Options) *Runtime {
 		shellPath = os.Getenv("SHELL")
 	}
 	if shellPath == "" {
-		shellPath = "/bin/zsh"
+		shellPath = "/bin/sh"
 	}
 	return &Runtime{binary: binary, timeout: timeout, shell: shellPath, runner: execRunner{}}
 }
 
 func (r *Runtime) Create(ctx context.Context, cfg ports.RuntimeConfig) (ports.RuntimeHandle, error) {
-	id := string(cfg.SessionID)
-	if err := validateSessionID(id); err != nil {
+	id, err := tmuxSessionName(cfg.SessionID)
+	if err != nil {
 		return ports.RuntimeHandle{}, err
 	}
 	if cfg.WorkspacePath == "" {
@@ -94,14 +97,11 @@ func (r *Runtime) Destroy(ctx context.Context, handle ports.RuntimeHandle) error
 	if err != nil {
 		return err
 	}
-	alive, err := r.IsAlive(ctx, handle)
-	if err != nil {
-		return err
-	}
-	if !alive {
-		return nil
-	}
 	if _, err := r.run(ctx, killSessionArgs(id)...); err != nil {
+		var exitErr *exec.ExitError
+		if errors.As(err, &exitErr) {
+			return nil
+		}
 		return fmt.Errorf("tmux runtime: destroy session %s: %w", id, err)
 	}
 	return nil
@@ -205,6 +205,43 @@ func (r *Runtime) run(ctx context.Context, args ...string) ([]byte, error) {
 	return out, nil
 }
 
+func tmuxSessionName(id domain.SessionID) (string, error) {
+	raw := string(id)
+	if raw == "" {
+		return "", errors.New("tmux runtime: session id is required")
+	}
+	if sessionIDPattern.MatchString(raw) {
+		return raw, nil
+	}
+	return sanitizedSessionName(raw), nil
+}
+
+func sanitizedSessionName(raw string) string {
+	var b strings.Builder
+	lastDash := false
+	for _, r := range raw {
+		valid := (r >= 'a' && r <= 'z') || (r >= 'A' && r <= 'Z') || (r >= '0' && r <= '9') || r == '_' || r == '-'
+		if valid {
+			b.WriteRune(r)
+			lastDash = false
+			continue
+		}
+		if !lastDash {
+			b.WriteByte('-')
+			lastDash = true
+		}
+	}
+	base := strings.Trim(b.String(), "-")
+	if base == "" {
+		base = "session"
+	}
+	if len(base) > 40 {
+		base = strings.TrimRight(base[:40], "-")
+	}
+	sum := sha256.Sum256([]byte(raw))
+	return base + "-" + hex.EncodeToString(sum[:4])
+}
+
 func validateSessionID(id string) error {
 	if id == "" {
 		return errors.New("tmux runtime: session id is required")
diff --git a/backend/internal/adapters/runtime/tmux/tmux_test.go b/backend/internal/adapters/runtime/tmux/tmux_test.go
index 1d4616099..cb56db35f 100644
--- a/backend/internal/adapters/runtime/tmux/tmux_test.go
+++ b/backend/internal/adapters/runtime/tmux/tmux_test.go
@@ -12,6 +12,14 @@ import (
 	"github.com/aoagents/agent-orchestrator/backend/internal/ports"
 )
 
+func TestNewDefaultsToPortableShell(t *testing.T) {
+	t.Setenv("SHELL", "")
+	r := New(Options{})
+	if got, want := r.shell, "/bin/sh"; got != want {
+		t.Fatalf("default shell = %q, want %q", got, want)
+	}
+}
+
 func TestCommandBuilders(t *testing.T) {
 	if got, want := newSessionArgs("sess-1", "/tmp/ws", "/bin/zsh", "echo hi"), []string{"new-session", "-d", "-s", "sess-1", "-c", "/tmp/ws", "/bin/zsh", "-lc", "echo hi"}; !reflect.DeepEqual(got, want) {
 		t.Fatalf("newSessionArgs = %#v, want %#v", got, want)
@@ -33,6 +41,22 @@ func TestExactTargets(t *testing.T) {
 	}
 }
 
+func TestTmuxSessionNameSanitizesIssueRefs(t *testing.T) {
+	got, err := tmuxSessionName("repo/issue#42.1")
+	if err != nil {
+		t.Fatalf("tmuxSessionName: %v", err)
+	}
+	if err := validateSessionID(got); err != nil {
+		t.Fatalf("sanitized id %q is invalid: %v", got, err)
+	}
+	if !strings.HasPrefix(got, "repo-issue-42-1-") {
+		t.Fatalf("sanitized id = %q, want readable prefix", got)
+	}
+	if got == "repo/issue#42.1" {
+		t.Fatal("sanitized id still contains raw unsafe characters")
+	}
+}
+
 func TestValidateSessionID(t *testing.T) {
 	valid := []string{"sess-1", "S_2", "abc123"}
 	for _, id := range valid {
@@ -104,6 +128,30 @@ func TestCreateRunsNewSessionAndDisablesStatus(t *testing.T) {
 	}
 }
 
+func TestCreateNormalizesUnsafeSessionID(t *testing.T) {
+	fr := &fakeRunner{}
+	r := New(Options{Binary: "tmux-test", Timeout: time.Second, Shell: "/bin/sh"})
+	r.runner = fr
+
+	handle, err := r.Create(context.Background(), ports.RuntimeConfig{
+		SessionID:     "repo/issue#42",
+		WorkspacePath: "/tmp/ws",
+		LaunchCommand: "echo ready",
+	})
+	if err != nil {
+		t.Fatalf("Create: %v", err)
+	}
+	if err := validateSessionID(handle.ID); err != nil {
+		t.Fatalf("handle id %q invalid: %v", handle.ID, err)
+	}
+	if handle.ID == "repo/issue#42" {
+		t.Fatal("handle kept unsafe raw session id")
+	}
+	if got := fr.calls[0].args[3]; got != handle.ID {
+		t.Fatalf("tmux session arg = %q, want handle id %q", got, handle.ID)
+	}
+}
+
 func TestSendMessageUsesLiteralForShortInput(t *testing.T) {
 	fr := &fakeRunner{}
 	r := New(Options{Timeout: time.Second})
@@ -164,8 +212,8 @@ func TestDestroyIsIdempotentWhenSessionMissing(t *testing.T) {
 	if err := r.Destroy(context.Background(), ports.RuntimeHandle{ID: "sess-1", RuntimeName: runtimeName}); err != nil {
 		t.Fatalf("Destroy: %v", err)
 	}
-	if len(fr.calls) != 1 || fr.calls[0].args[0] != "has-session" {
-		t.Fatalf("calls = %#v, want only has-session", fr.calls)
+	if len(fr.calls) != 1 || fr.calls[0].args[0] != "kill-session" {
+		t.Fatalf("calls = %#v, want only kill-session", fr.calls)
 	}
 }