Improve graph visualization for multi-parent (AND-join) node dependencies

[Hong-Sung]

Problem

Currently, when using add_edge(["b_2", "c"], "d") to define that node d should only run after both b_2 and c complete, the visual representation shows two independent arrows: b_2 → d and c → d.

This creates confusion because it visually resembles two independent triggers (OR behavior), suggesting that d might run after either b_2 or c, even though the actual behavior is correct (AND-join).

Why it matters

• This can easily mislead users who rely on the diagram to understand execution logic.
• It is especially problematic when explaining workflows to teams, debugging or onboarding new engineers.
• Visuals should match execution semantics.

Suggestion

Consider one of the following enhancements:

1. Visual join indicator:
   Use an intermediate visual "join" node or a converging edge to show that d depends on both parents together.

2. Annotated labels:
   Allow an option to render small notes like d (waits for: b_2, c) directly in the graph.

3. Strict mode drawing:
   Introduce a flag in graph.get_graph().draw() or draw_ascii() like strict=True, which shows compound dependencies more clearly.

Example

Given:

builder.add_edge(["b_2", "c"], "d")
The current diagram:

b_2 → d
c   → d
Should be replaced with something like:

b_2 ─┐
     ├─▶ [AND] ─▶ d
c   ─┘
Or annotated accordingly.

Final note
This is a visual-only concern — execution is currently correct.
But improving this would help avoid misunderstanding, especially in production workflows and educational contexts.