pcbPath chooses top when a plated-hole start connects to an explicit bottom via port

Environment: @tscircuit/core 0.0.1892, @tscircuit/props 0.0.649, circuit-json 0.0.484, Bun 1.4.2, Linux.

A manual pcbPath from a plated contact to an explicit via .bottom port is emitted entirely on top. Reversing the same endpoints emits it on bottom. In a two-layer board this silently changed saved bottom crossings into top copper shorts. Our independent saved-route comparison and native KiCad DRC caught it.

Expected: choose a layer available at both endpoint ports (bottom in this case), or reject an incompatible path. An explicit trace-level pcbLayer would also make PTH-to-PTH layer selection possible without adding a physical via.

Reproduction (bun repro.tsx):

import React from 'react'
import {Circuit} from '@tscircuit/core'
import {writeFileSync} from 'node:fs'

for(const reverse of [false,true]){
 const circuit=new Circuit()
 circuit.add(<board width={10} height={10} layers={2} schematicDisabled>
  <net name="SIGNAL"/>
  <chip name="J1" pcbX={-2} pinLabels={{pin1:['SIGNAL']}} footprint={<footprint>
   <platedhole portHints={['1']} shape="circle" outerDiameter={1.4} holeDiameter={.8}/>
  </footprint>}/>
  <via name="V1" pcbX={2} holeDiameter={.3} outerDiameter={.6} fromLayer="top" toLayer="bottom" connectsTo="net.SIGNAL"/>
  <trace from="J1.pin1" to="net.SIGNAL"/>
  <trace name="PATH" from={reverse?'.V1 > .bottom':'J1.pin1'} to={reverse?'J1.pin1':'.V1 > .bottom'}
   pcbPath={[{x:reverse?-2:2,y:1}]} thickness={.25}/>
 </board>)
 await circuit.renderUntilSettled()
 const data=circuit.getCircuitJson()
 const source=data.find((r:any)=>r.type==='source_trace'&&r.name==='PATH') as any
 const trace=data.find((r:any)=>r.type==='pcb_trace'&&r.source_trace_id===source.source_trace_id) as any
 const layers=[...new Set(trace.route.filter((p:any)=>p.route_type==='wire').map((p:any)=>p.layer))]
 console.log(JSON.stringify({reverse,layers}))
 writeFileSync(new URL(reverse?'via-first.json':'pth-first.json',import.meta.url),JSON.stringify(data,null,2)+'\n')
}

Actual output:

{"reverse":false,"layers":["top"]}
{"reverse":true,"layers":["bottom"]}

In the installed core implementation, manual path emission initializes currentLayer from anchorPort.getAvailablePcbLayers()[0]; the explicit bottom endpoint does not constrain that selection. Current props expose no trace-level layer override.

Local workaround: begin bottom paths at an explicit via bottom port, and restructure the bottom tree to avoid PTH-to-PTH edges. Saved route geometry/layer checks now fail closed before native export. This workaround is implemented locally; no upstream implementation PR yet.

Run bun repro.tsx and inspect the manual path emission where currentLayer is initialized from anchorPort.getAvailablePcbLayers()[0]. Add regression coverage for both endpoint orders, then verify that compatible endpoints use the shared layer or that incompatible paths are rejected, without changing the reported saved-route expectations.