ELK layout with mergeEdges enabled does not render correctly in subgraphs

[raijinsetsu]

Describe the bug
When using mermaid.ai, setting the configuration, as described below, does not merge the edges subgraphs.

To Reproduce
Use this chart:

---
config:
    layout: elk
    elk:
        mergeEdges: true
---
flowchart TD
    %% first workaround attempt
    A
    B
    C

    subgraph S1
        A & B --> C
    end

    %% second workaround attempt
    subgraph S2
        D
        E
        F
    end

    D & E -->  F

Expected behavior
The the subgraphs should render the same as:

---
config:
    layout: elk
    elk:
        mergeEdges: true
---
flowchart TD
    A & B --> C

    D & E -->  F

Desktop (please complete the following information):

• OS: MacOS
• Browser: Chrome
• Version: 147.0.7727.57

[rajat-ht]

@raijinsetsu, Thanks for reporting this issue and for providing a detailed reproduction example. Since this appears to be related to the open-source Mermaid renderer, I’ve duplicated the issue in the open-source repository for further investigation by the team.