Fetch today's tasks asynchronously on entering planning

The controller fetches the Marvin task list when entering planning,
mirroring the planning coach: generation-guarded goroutine, status enum
(idle/pending/ready/error), projected into State only while planning and
only when a provider is set. nil provider degrades to no tasks view.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

internal/session/session_test.go

@@ -13,6 +13,7 @@ import (
 	"antidrift/internal/domain"
 	"antidrift/internal/evidence"
 	"antidrift/internal/store"
+	"antidrift/internal/tasks"
 )
 
 func newTestController(t *testing.T) (*Controller, string) {
@@ -772,3 +773,73 @@ func TestRecentTitlesRingCapsAtTen(t *testing.T) {
 		t.Fatalf("ring should drop oldest first, got first=%q", titles[0])
 	}
 }
+
+type fakeProvider struct {
+	list []tasks.Task
+	err  error
+	gate chan struct{} // if non-nil, Today blocks until it receives
+}
+
+func (f *fakeProvider) Today(ctx context.Context) ([]tasks.Task, error) {
+	if f.gate != nil {
+		<-f.gate
+	}
+	return f.list, f.err
+}
+
+// waitTasksStatus polls until the tasks view reaches want, or fails after 2s.
+func waitTasksStatus(t *testing.T, c *Controller, want string) State {
+	t.Helper()
+	deadline := time.Now().Add(2 * time.Second)
+	for time.Now().Before(deadline) {
+		st := c.State()
+		if st.Tasks != nil && st.Tasks.Status == want {
+			return st
+		}
+		time.Sleep(5 * time.Millisecond)
+	}
+	t.Fatalf("tasks status never reached %q (last: %+v)", want, c.State().Tasks)
+	return State{}
+}
+
+func TestEnterPlanningFetchesTasks(t *testing.T) {
+	c, _ := newTestController(t)
+	c.SetTasks(&fakeProvider{list: []tasks.Task{{ID: "a", Title: "Write spec", Day: "2026-05-31"}}})
+	if err := c.EnterPlanning(); err != nil {
+		t.Fatalf("enter planning: %v", err)
+	}
+	st := waitTasksStatus(t, c, "ready")
+	if len(st.Tasks.Tasks) != 1 || st.Tasks.Tasks[0].Title != "Write spec" {
+		t.Fatalf("tasks list wrong: %+v", st.Tasks)
+	}
+}
+
+func TestTasksFetchError(t *testing.T) {
+	c, _ := newTestController(t)
+	c.SetTasks(&fakeProvider{err: errors.New("am down")})
+	if err := c.EnterPlanning(); err != nil {
+		t.Fatalf("enter planning: %v", err)
+	}
+	st := waitTasksStatus(t, c, "error")
+	if len(st.Tasks.Tasks) != 0 {
+		t.Fatalf("error state should carry no tasks: %+v", st.Tasks)
+	}
+}
+
+func TestNoProviderNoTasksView(t *testing.T) {
+	c, _ := newTestController(t)
+	if err := c.EnterPlanning(); err != nil {
+		t.Fatalf("enter planning: %v", err)
+	}
+	if c.State().Tasks != nil {
+		t.Fatalf("nil provider should yield no tasks view: %+v", c.State().Tasks)
+	}
+}
+
+func TestTasksViewAbsentOutsidePlanning(t *testing.T) {
+	c, _ := newTestController(t)
+	c.SetTasks(&fakeProvider{list: []tasks.Task{{ID: "a", Title: "x"}}})
+	if c.State().Tasks != nil {
+		t.Fatalf("no tasks view while Locked: %+v", c.State().Tasks)
+	}
+}