Keep duplicated ports on finite shared region edges

[AnasSarkiz]

Duplicating a congested port between offset rectangles used a direction perpendicular to their centers. That direction can leave the shared edge, and an offset near its endpoint can leave the finite boundary entirely.

Compute the shared edge from the intersection of the region bounds and place duplicates along its available length. This preserves both region membership and distinct port positions without changing routing thresholds.

Before / after

Actual output from the regression test on main 7745c91 and this branch; the gray line marks the shared edge.

Before: duplicate leaves the boundary	After: duplicate stays on the shared edge

Validation

• All 127 tests pass; the new regression fails on main.
• Regression covers horizontal and vertical boundaries, including an exact endpoint and a point near it.
• Typecheck, format check and build pass.

Extracted as an independent fix from #193. This PR does not claim to resolve all SRJ18 Pipeline 9 failures; downstream DRC and same-machine benchmark validation remain necessary.

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Project	Deployment	Actions	Updated
tiny-hypergraph	Ready	Preview	Sep 17, 2026 7:11pm UTC

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