ngspice not found: install it and ensure it's on PATH.
macOS: brew install ngspice
Ubuntu: sudo apt install -y ngspice
Windows: install Spice64 and add the bin to PATH
Binary RAW: Binary RAW not supported yet → we force ASCII in our runner, but if you
run NGSpice manually, set set filetype=ascii in a .control block or use -r.
Unconnected port: connect every component port to a Net or another Port before building.
Missing .model for switches: add directives with circuit.add_directive(".model ...").
AC analysis looks flat or phase missing: ensure you use small-signal sources (VA/Iac),
or reconstruct complex traces with ac_gain_phase which handles re/im or mag/phase.