fix(elk): scope rounded edge curve to ELK layout only

[knsv-bot]

Summary

Scopes the fix from #7425 (issue #7213) so that the rounded curve is only applied when the ELK layout algorithm is used, rather than changing the global default for all flowcharts.

• Reverts the global flowchart.curve default from 'rounded' back to 'basis'
• Sets edge.curve = 'rounded' on each ELK edge right before insertEdge, ensuring ELK's orthogonal routes render with right-angle segments and rounded corners
• Non-ELK layouts are completely unaffected

Resolves #7213

Test plan

• Unit tests pass (973 flowchart + edge tests)
• Config type verification passes
• Build passes (no TS errors)
• Visual verification — ELK edges route orthogonally with rounded corners
• Cypress e2e snapshots
• CI passes (lint, unit, e2e, type-check)

🤖 Generated with Claude Code

[changeset-bot]

⚠️ No Changeset found

Latest commit: 4c968e2

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[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 3.53%. Comparing base (547e6d5) to head (4c968e2).
⚠️ Report is 448 commits behind head on master.

Files with missing lines	Patch %	Lines
packages/mermaid-layout-elk/src/render.ts	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##           master   #7454      +/-   ##
=========================================
- Coverage    3.59%   3.53%   -0.06%     
=========================================
  Files         475     493      +18     
  Lines       47191   49010    +1819     
  Branches      735     769      +34     
=========================================
+ Hits         1696    1734      +38     
- Misses      45495   47276    +1781     

Flag	Coverage Δ
unit	3.53% <0.00%> (-0.06%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
packages/mermaid-layout-elk/src/render.ts	0.12% <0.00%> (-0.01%)	⬇️

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[ashishjain0512]

[sisyphus-bot]

Clean, focused fix — this is exactly the right scope for the ELK edge curve issue.

Note: PR targets master. This appears to be an intentional hotfix by the maintainer. Also note that PR #7452 covers this same fix bundled with other changes — worth clarifying which PR supersedes the other.

What's working well

🎉 [praise] Excellent scoping — the fix is isolated to just 3 files with no collateral changes. Reverting the global default to basis in config.schema.yaml:2160 and setting edge.curve = 'rounded' only in the ELK render path (render.ts:1073) is the cleanest possible approach.

🎉 [praise] Good explanatory comment on the edge.curve = 'rounded' line — "ELK produces orthogonal edge routes" explains the why, not just the what.

🎉 [praise] The changeset correctly scopes to both mermaid and @mermaid-js/mermaid-layout-elk packages with patch bumps. The description clearly communicates what changed and what's unaffected.

Things to address

🟡 [important] The PR checklist shows unchecked items for Cypress e2e snapshots and CI. Since this changes the rendering behavior of ELK edges, visual regression verification is important — especially to confirm that the original issue (#7213, curved ELK edges) is resolved and that non-ELK flowcharts are visually unchanged. It would be great to confirm CI passes cleanly before merge.

💡 [suggestion] Consider adding a Cypress e2e test case using the reproduction diagram from issue #7213 (the flowchart with subgraphs G1/G2 and repeated N11 --- N22 edges). This would prevent regression of this specific fix and serve as documentation that ELK edge routing is intentionally orthogonal.

Security

No XSS or injection issues. This PR only modifies a config default value and sets a string property (edge.curve) on an internal edge object. No user input handling, DOM manipulation, or sanitization changes.

Self-check

• At least one 🎉 [praise] item exists (3)
• No duplicate comments
• Severity tally: 0 🔴 blocking / 1 🟡 important / 0 🟢 nit / 1 💡 suggestion / 3 🎉 praise
• Verdict: COMMENT (1 🟡 — e2e verification pending)
• Not a draft PR
• No inline comments used
• Tone check: constructive, appreciative

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Build	Status	Details	Updated (UTC)
default (Inspect)	👍 Changes approved	401 changed	Mar 5, 2026, 3:55 PM

[knsv]

The e2e test is there already

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