Detect connected source ports missing PCB mappings

[AnasSarkiz]

Summary

• add checkSourcePortsHavePcbPorts to placement validation
• report pcb_port_not_matched_error when a connected, PCB-backed source port lacks an owner-matched PCB port
• follow internal pin connectivity while avoiding cascades for known footprint-load failures
• export and document the checker, with regression coverage for mapping and false-positive edge cases

Root cause

The existing routing checks begin from pcb_port records or filter out source ports without a PCB mapping. Removing a pcb_port therefore also removed the evidence those checks needed, so runAllPlacementChecks returned no error.

Impact

Placement validation now diagnoses missing physical port mappings before routing. Unconnected ports, source-only circuits, and components with explicit footprint-load failures remain unaffected.

Testing

• bun test — 186 passed, 0 failed
• bun run build
• Biome check on changed TypeScript files
• git diff --check

[imrishabh18]

IIUC this is a core bug if you see this issue

[seveibar]

Visual Snapshot? This does not seem like a user bug but a core bug?

[AnasSarkiz]

Moved the Core-owned producer invariant to tscircuit/core#3354 based on this review and the natural MangoPi repro.

The trace confirmed that the imported thermalpad alias is erased by the generated wrapper's prop spread before Core receives the <chip>, so Core cannot reconstruct pin 89/9 without heuristic pad-order inference. The Core PR now reports the canonical error after port matching settles and blocks autorouting. The importer generator still needs a separate per-pin alias merge.

This draft should not merge unchanged alongside core#3354 because both implementations would emit the same placement diagnostic.