Migrate the coach fetch onto runFetchAsync

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

internal/session/roles.go

@@ -357,16 +357,12 @@ func (c *Controller) RequestCoach(intent string) error {
 	c.mu.Unlock()
 	c.notify()
 
-	go func() {
-		ctx, cancel := context.WithTimeout(context.Background(), coachTimeout)
-		defer cancel()
-		prop, err := coach.Coach(ctx, intent, grounding)
-
-		c.mu.Lock()
-		if gen != c.coachGen || c.runtimeState != domain.RuntimePlanning {
-			c.mu.Unlock()
-			return // stale or left planning: discard
-		}
+	var prop ai.Proposal
+	var err error
+	c.runFetchAsync(coachTimeout,
+		func(ctx context.Context) { prop, err = coach.Coach(ctx, intent, grounding) },
+		func() bool { return gen != c.coachGen || c.runtimeState != domain.RuntimePlanning },
+		func() {
 			if err != nil {
 				c.coachStatus = coachError
 				c.coachErr = coachErrorMessage(err)
@@ -376,9 +372,7 @@ func (c *Controller) RequestCoach(intent string) error {
 				c.coachProposal = &prop
 				c.coachErr = ""
 			}
-		c.mu.Unlock()
-		c.notify()
-	}()
+		})
 	return nil
 }