feat(tools): add exec tool enhancement with background execution and PTY support (#1752)

- Unified exec tool with actions: run/list/poll/read/write/send-keys/kill
- PTY support using creack/pty library
- Process session management with background execution
- Process group kill for cleaning up child processes
- Session cleanup: 30-minute TTL for old sessions
- Output buffer: 100MB limit with truncation

Actions:
- run: execute command (sync or background)
- list: list all sessions
- poll: check session status
- read: read session output
- write: send input to session stdin
- send-keys: send special keys (up, down, ctrl-c, enter, etc.)
- kill: terminate session

Tests:
- PTY: allowed commands, write/read, poll, kill, process group kill
- Non-PTY: background execution, list, read, write, poll, kill, process group kill
- Session management: add/get/remove/list/cleanup

pkg/tools/session_test.go

@@ -0,0 +1,99 @@
+package tools
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestSessionManager_AddGet(t *testing.T) {
+	sm := NewSessionManager()
+	session := &ProcessSession{
+		ID:        "test-1",
+		Command:   "echo hello",
+		Status:    "running",
+		StartTime: 1000,
+	}
+
+	sm.Add(session)
+
+	got, err := sm.Get("test-1")
+	require.NoError(t, err)
+	require.Equal(t, "test-1", got.ID)
+}
+
+func TestSessionManager_Remove(t *testing.T) {
+	sm := NewSessionManager()
+	session := &ProcessSession{
+		ID:        "test-1",
+		Command:   "echo hello",
+		Status:    "running",
+		StartTime: 1000,
+	}
+	sm.Add(session)
+	sm.Remove("test-1")
+
+	_, err := sm.Get("test-1")
+	require.ErrorIs(t, err, ErrSessionNotFound)
+}
+
+func TestSessionManager_List(t *testing.T) {
+	sm := NewSessionManager()
+	sm.Add(&ProcessSession{
+		ID:        "test-1",
+		Command:   "echo hello",
+		Status:    "running",
+		StartTime: 1000,
+	})
+	sm.Add(&ProcessSession{
+		ID:        "test-2",
+		Command:   "echo world",
+		Status:    "running",
+		StartTime: 1001,
+	})
+	sm.Add(&ProcessSession{
+		ID:        "test-3",
+		Command:   "echo done",
+		Status:    "done",
+		StartTime: 1002,
+	})
+
+	sessions := sm.List()
+	require.Len(t, sessions, 3)
+
+	ids := make(map[string]bool)
+	for _, s := range sessions {
+		ids[s.ID] = true
+	}
+	require.True(t, ids["test-1"])
+	require.True(t, ids["test-2"])
+	require.True(t, ids["test-3"])
+}
+
+func TestProcessSession_IsDone(t *testing.T) {
+	session := &ProcessSession{Status: "running"}
+	require.False(t, session.IsDone())
+
+	session.Status = "done"
+	require.True(t, session.IsDone())
+
+	session.Status = "exited"
+	require.True(t, session.IsDone())
+}
+
+func TestProcessSession_ToSessionInfo(t *testing.T) {
+	session := &ProcessSession{
+		ID:        "test-1",
+		PID:       12345,
+		Command:   "echo hello",
+		Status:    "running",
+		StartTime: 1000,
+	}
+
+	info := session.ToSessionInfo()
+	require.Equal(t, "test-1", info.ID)
+	require.Equal(t, "echo hello", info.Command)
+	require.Equal(t, "running", info.Status)
+	require.Equal(t, 12345, info.PID)
+	require.Equal(t, int64(1000), info.StartedAt)
+}