Previous flashes on macOS shipped the USB with NO wifi_creds.json at all — so every freshly-flashed stick booted a device that couldn't connect to any of the 4 standard presets the Linux oven/ac-os path bakes in, and re-flashes wiped out any user-added networks from the prior session. Two-step mirror of ac_media_write_global_wifi_creds + ac_media_merge_wifi_creds from scripts/media-layout.sh: 1. Preset list, inlined in the script (kept in sync with the JSON in media-layout.sh:140 — aesthetic.computer / ATT2AWTpcr / GettyLink / Tondo_Guest). Written on every flash even for a never-flashed stick. 2. Before the partitioning wipe, read the existing wifi_creds.json off the target (if present) into /tmp/ac-wifi-preserve.*.json. After mount, merge preset + preserved with Python one-liner: dedupe by SSID, preserved entries override presets for the same SSID (so user-saved passwords survive a re-flash). Both partitions (ACBOOT + ACEFI) get the same merged file. If the caller stages their own wifi_creds.json at ${SRC_DIR}/wifi_creds.json (e.g. /tmp/ac-os-pull/wifi_creds.json) that file wins as source-of-truth and neither preset nor preserved merge is applied. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>