fix(tidy-tree): keep mindmap edges connected to a non-circular root

[knsv-bot]

Summary

Resolves #7572

In the tidy-tree layout, calculateEdgePositions only added an intermediate routing point for source/target nodes whose section was 'left' or 'right'. For root-sourced edges (section === 'root') no intermediate was pushed, so the post-loop intersection recompute used the child's center as the reference and could land the start anchor on the root's top/bottom edge — visually disconnecting the link from the root. The cloud root only appeared correct by coincidence of its rounded silhouette.

• Added 'root' branches to both the source and target intermediate-point blocks in calculateEdgePositions. The root-side intermediate is placed on the side of the root facing the other node's section (left → -x, right → +x), at y = root.y.
• Added a unit test that asserts root-sourced edges include the side-facing intermediate (with both generic sign-agreement and exact-coordinate checks).
• Added an E2E imgSnapshotTest using the exact reproduction from the issue.

Classification

• Change type: layout algorithm (@mermaid-js/layout-tidy-tree)
• Breaking change: no — internal function; the rendered diff is the bug fix itself
• Shared code touched: no — change is contained in the tidy-tree layout package

Verification

• TDD: test failed before fix (expected -30 to be 20), passes after
• Lint: passed
• Unit tests: passed (pnpm vitest run packages/mermaid-layout-tidy-tree — 14/14)
• E2E snapshot test: added in cypress/integration/rendering/mindmap-tidy-tree.spec.js (5-tidy-tree)
• comp-review-changes: passed (0 blockers, 0 warnings, 1 info — expected Argos diff for non-circle-root tidy-tree mindmaps; this is the intent of the fix)
• Visual spot-check: not run locally — geometric correctness is asserted directly by the unit test; Argos provides visual confirmation in CI
• Full e2e: not run locally — deferred to CI
• Changeset: generated (patch) for @mermaid-js/layout-tidy-tree and mermaid

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🦋 Changeset detected

Latest commit: 81be6af

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

This PR includes changesets to release 2 packages

Name	Type
@mermaid-js/layout-tidy-tree	Patch
mermaid	Patch

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commit: 81be6af

[codecov]

Codecov Report

❌ Patch coverage is 0% with 24 lines in your changes missing coverage. Please review.
✅ Project coverage is 3.31%. Comparing base (5969033) to head (81be6af).
⚠️ Report is 5 commits behind head on develop.

Files with missing lines	Patch %	Lines
packages/mermaid-layout-tidy-tree/src/layout.ts	0.00%	24 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           develop   #7639      +/-   ##
==========================================
- Coverage     3.31%   3.31%   -0.01%     
==========================================
  Files          539     540       +1     
  Lines        56664   56699      +35     
  Branches       824     824              
==========================================
  Hits          1880    1880              
- Misses       54784   54819      +35     

Flag	Coverage Δ
unit	3.31% <0.00%> (-0.01%)	⬇️

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Files with missing lines	Coverage Δ
packages/mermaid-layout-tidy-tree/src/types.ts	100.00% <ø> (ø)
packages/mermaid-layout-tidy-tree/src/layout.ts	0.21% <0.00%> (-0.02%)	⬇️

... and 1 file with indirect coverage changes

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Build	Status	Details	Updated (UTC)
default (Inspect)	👍 Changes approved	5 changed, 1 added	Apr 21, 2026, 9:25 AM