Wires the second half of the mixed-mode event loop on top of the
voltage cache that step 1 added.
Step 2 — loadCircuit + resolveDc:
- `loadCircuit(netlist, pinNetMap)` accepts the artifacts that
NetlistBuilder already produces, boots the engine lazily, calls
`loadNetlist`, and clears the voltage cache so stale values from a
previous circuit cannot leak through.
- `resolveDc()` runs `op` and walks the pinNetMap, calling readVec for
each non-ground net and publishVoltage for each pin. Ground pins
short-circuit to 0 V without an extra round-trip. Missing nets are
skipped quietly so a disconnected probe pin can't break the resolve.
Step 3 — onMcuPinChange:
- Issues `alter V_<board>_<pin> dc <volts>` and re-resolves. Caller
decides the volts: `state ? vcc : 0` for plain digital, but boards
with open-drain / output-impedance semantics can pass any number.
- Silent no-op when no engine has been started, so legacy paths that
fire pinChange unconditionally can't crash the simulator.
NgSpiceClient interface added and exported so unit tests can inject a
fake engine that records alter() calls and returns canned readVec
values — `__setSchedulerEngineFactoryForTests`. 7 new tests cover the
load → resolve → alter → republish loop end-to-end without booting
the real WASM worker.
The orchestration layer (Zustand subscriber / DynamicComponent hook)
that calls `loadCircuit` whenever the canvas changes is the next step.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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