Adding dash to the gap from the left doesn't work

[AlexeyGirin]

Steps to Reproduce

1. Go to Macro - Sequence mode (clean canvas)
2. Load from HELM: RNA1{R(A)P.R(A)P.R(A)}|RNA2{R(U)}|RNA3{R(U)}$RNA1,RNA2,2:pair-2:pair|RNA1,RNA3,8:pair-2:pair$$$V2.0
   
3. Turn it to edit mode (sync mode on) move cursor the left from the gap in antisense
   
4. Press - key

Actual behavior
Nothing happens

Expected behavior
Dash (i.e. bond) should appear (i.e. established)

ADDITIONAL CASE: RNA1{R(A)P.R(A)}|RNA2{R(U)}|RNA3{R(U)}$RNA1,RNA2,2:pair-2:pair|RNA1,RNA3,5:pair-2:pair$$$V2.0

As per requirement:

3.4. The lines can only be added left of a gap. When the user exits "Edit" mode, if the line(s) do not connect monomer symbols, all lines should be deleted. If the lines(s) connect monomer symbols, a new backbone should be established.

Versions

• Ketcher Version 3.2.0-rc.4 Build at 2025-03-25; 16:50:39
• Indigo Version 1.30.0-rc.4.0-g552c98211-wasm32-wasm-clang-19.0.0
• Chrome Version 134.0.6998.178 (Official Build) (64-bit)
• Win10

Issue found while testing: #6254

[SefaBilgii]

This issue is reproducible

Ketcher Version: 3.6.0-rc.1
OS: MacOs Sequoia Version 15.5
Browser : Chrome Version 138.0.7204.169