autopilot: start threading contexts through

The `GraphSource` interface in the `autopilot` package is directly
implemented by the `graphdb.KVStore` and so we will eventually thread
contexts through to this interface. So in this commit, we start updating
the autopilot system to thread contexts through in preparation for
passing the context through to any calls made to the GraphSource.

Two context.TODOs are added here which will be addressed in follow up
commits.

autopilot/manager.go

@@ -1,11 +1,13 @@
 package autopilot
 
 import (
+	"context"
 	"fmt"
 	"sync"
 
 	"github.com/btcsuite/btcd/btcec/v2"
 	"github.com/btcsuite/btcd/wire"
+	"github.com/lightningnetwork/lnd/fn/v2"
 	graphdb "github.com/lightningnetwork/lnd/graph/db"
 	"github.com/lightningnetwork/lnd/lnwallet"
 	"github.com/lightningnetwork/lnd/lnwire"
@@ -53,8 +55,9 @@ type Manager struct {
 	// disabled.
 	pilot *Agent
 
-	quit chan struct{}
-	wg   sync.WaitGroup
+	quit   chan struct{}
+	wg     sync.WaitGroup
+	cancel fn.Option[context.CancelFunc]
 	sync.Mutex
 }
 
@@ -80,6 +83,7 @@ func (m *Manager) Stop() error {
 			log.Errorf("Unable to stop pilot: %v", err)
 		}
 
+		m.cancel.WhenSome(func(fn context.CancelFunc) { fn() })
 		close(m.quit)
 		m.wg.Wait()
 	})
@@ -96,7 +100,7 @@ func (m *Manager) IsActive() bool {
 
 // StartAgent creates and starts an autopilot agent from the Manager's
 // config.
-func (m *Manager) StartAgent() error {
+func (m *Manager) StartAgent(ctx context.Context) error {
 	m.Lock()
 	defer m.Unlock()
 
@@ -104,6 +108,8 @@ func (m *Manager) StartAgent() error {
 	if m.pilot != nil {
 		return nil
 	}
+	ctx, cancel := context.WithCancel(ctx)
+	m.cancel = fn.Some(cancel)
 
 	// Next, we'll fetch the current state of open channels from the
 	// database to use as initial state for the auto-pilot agent.
@@ -119,7 +125,7 @@ func (m *Manager) StartAgent() error {
 		return err
 	}
 
-	if err := pilot.Start(); err != nil {
+	if err := pilot.Start(ctx); err != nil {
 		return err
 	}
 
@@ -163,6 +169,8 @@ func (m *Manager) StartAgent() error {
 				return
 			case <-m.quit:
 				return
+			case <-ctx.Done():
+				return
 			}
 		}
 
@@ -233,6 +241,8 @@ func (m *Manager) StartAgent() error {
 				return
 			case <-m.quit:
 				return
+			case <-ctx.Done():
+				return
 			}
 		}
 	}()