6638:sequence diagram additional messages

[omkarht]

📑 Summary

This PR introduces enhanced arrowhead support in sequence diagrams, following Option B of the proposed syntax. The updates include:

• New arrowhead type: Solid half and Stick half, represented using -| and -\ and its variants.
• Support for half arrows:
  • Solid half arrows:
    • Top: -|\
    • Bottom: -|/
    • Reverse top: /|-
    • Reverse bottom: \|-

• Stick half arrows:
  • Top: -\\
  • Bottom: -//
  • Reverse top: //-
  • Reverse bottom: \\-

• Central connection circle support: append () after the arrow to indicate a central lifeline connection (e.g., ->(), -->>(), -|\(), etc.)
  

These enhancements improve visual expressiveness and maintain compatibility with our DSL, bringing us closer to parity with tools like PlantUML and Mermaid.

Resolves #6638

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• 📖 have read the contribution guidelines
• 💻 have added necessary unit/e2e tests.
• 📓 have added documentation. Make sure MERMAID_RELEASE_VERSION is used for all new features.
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[changeset-bot]

🦋 Changeset detected

Latest commit: b75dcb8

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

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commit: b75dcb8

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Build	Status	Details	Updated (UTC)
default (Inspect)	👍 Changes approved	1 changed, 24 added	Sep 23, 2025, 7:22 AM

[codecov]

Codecov Report

❌ Patch coverage is 0% with 315 lines in your changes missing coverage. Please review.
✅ Project coverage is 3.55%. Comparing base (d5c4eff) to head (b75dcb8).
⚠️ Report is 40 commits behind head on develop.

Files with missing lines	Patch %	Lines
.../mermaid/src/diagrams/sequence/sequenceRenderer.ts	0.00%	209 Missing ⚠️
packages/mermaid/src/diagrams/sequence/svgDraw.js	0.00%	71 Missing ⚠️
...ckages/mermaid/src/diagrams/sequence/sequenceDb.ts	0.00%	35 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           develop   #6789      +/-   ##
==========================================
- Coverage     3.57%   3.55%   -0.03%     
==========================================
  Files          473     474       +1     
  Lines        47139   47453     +314     
  Branches       730     730              
==========================================
  Hits          1687    1687              
- Misses       45452   45766     +314     

Flag	Coverage Δ
unit	3.55% <0.00%> (-0.03%)	⬇️

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Files with missing lines	Coverage Δ
packages/mermaid/src/diagrams/sequence/types.ts	100.00% <ø> (ø)
...ckages/mermaid/src/diagrams/sequence/sequenceDb.ts	0.00% <0.00%> (ø)
packages/mermaid/src/diagrams/sequence/svgDraw.js	0.00% <0.00%> (ø)
.../mermaid/src/diagrams/sequence/sequenceRenderer.ts	0.06% <0.00%> (-0.01%)	⬇️

... and 1 file with indirect coverage changes

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[sidharthv96]

Alignment of the right arrowhead or dotted line is incorrect

[omkarht]

Alignment of the right arrowhead or dotted line is incorrect

@sidharthv96 , I have resolved this one in e3ef5e4