Fork tasks from snapshots; snapshot only when text follows tool calls

internal/agents/guidance.go

@@ -59,12 +59,26 @@ func (m *Manager) bounceProseQuestion(l *live) claude.HookFunc {
 	}
 }
 
-func taskGuidance(task api.Task) string {
-	if task.TodoItem == nil {
-		return guidance
+func (m *Manager) taskGuidance(ctx context.Context, task api.Task) (string, error) {
+	g := guidance
+	if task.TodoItem != nil {
+		g += fmt.Sprintf("\n- This task was started from the item %q in %s at the repo root. When the work is done, remove that item from %s in this worktree, so the removal lands in the same merge as the work.",
+			*task.TodoItem, todo.File, todo.File)
 	}
-	return guidance + fmt.Sprintf("\n- This task was started from the item %q in %s at the repo root. When the work is done, remove that item from %s in this worktree, so the removal lands in the same merge as the work.",
-		*task.TodoItem, todo.File, todo.File)
+	if task.ForkedFrom == nil {
+		return g, nil
+	}
+	src, err := m.store.GetTask(ctx, *task.ForkedFrom)
+	if err != nil {
+		return "", err
+	}
+	return g + forkGuidance(task, src), nil
+}
+
+func forkGuidance(task, src api.Task) string {
+	return fmt.Sprintf("\n- This conversation was forked from byre task %q at its snapshot %d, into a task of its own: branch %s, worktree %s, which held that snapshot's files when the fork was made. "+
+		"Everything before the fork happened in %s, which belongs to the other task: from now on read and change files only in %s, never in the other worktree, and use paths under it.",
+		src.Title, *task.ForkedAt, task.Branch, task.WorktreePath, src.WorktreePath, task.WorktreePath)
 }
 
 func remindGuidance(text string) claude.HookFunc {