On the last page, Elara wrote a dedication she had never noticed before, hidden under the index: “For the curious. May you learn why, then learn how.”

And on her own workbench, behind the oscilloscope and the spool of lead-free solder, sat the same 4th Edition. Open. Coffee-stained. Annotated in two handwritings.

Leo thought back to a YouTube video she’d half-watched. “Heat. And reverse voltage.”

They turned to page 287. A real photograph of a burned PCB. Next to it, a flowchart: Troubleshooting a Non-Functioning Motor Drive. Step 3 was underlined in red pen: Check the filter capacitor for bulging or leakage.