fix: connect manual pcbPath vias on both layers

[seveibar]

Summary

• emit an aligned wire point on each side of every manual pcbPath via
• make consecutive via entries produce the intended intervening copper segment
• reuse explicit same-position wire points so the documented workaround remains compatible without zero-length duplicates
• reject a manual via whose fromLayer disagrees with the current path layer before malformed copper is emitted

Why

A pcbPath containing consecutive vias previously serialized as wire -> via -> via -> wire. There was no wire on the layer between those vias, so Gerber output omitted the intended connecting copper while the source still looked fully specified.

This was reproduced while fixing the reviewed USB-C fan-in in tscircuit/quick-configure. The shared validation companion, tscircuit/checks#232, makes malformed raw Circuit JSON fail closed; this PR fixes the producing path in core.

Compatibility

Existing paths that already place ordinary points at the via coordinates keep the same effective route. Exact same-position/same-layer wire points are deduplicated, while distinct corners and layer changes are preserved.

Validation

• bun test --timeout 9999999 — 1,432 pass, 40 skip, 0 fail
• focused manual pcbPath suite — 4 pass, 0 fail
• snapshots for consecutive vias, explicit-wire compatibility, and invalid via direction
• bunx tsc --noEmit
• bun run build

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Project	Deployment	Actions	Updated (UTC)
tscircuit-core-benchmarks	Ready	Preview	Aug 22, 2026 7:48am

[github-actions]

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