The trick everyone misses: you don't need to keep the blocklist in RAM. Store the domains as sorted 40-bit hashes in flash and binary-search them. 140,000+ domains fit in ~0.7 MB of flash and are matched in ~10 ms, using ~50 KB of RAM.
Why 40 bits? It's the sweet spot for this flash budget. Collisions follow the birthday bound — at 141k domains you get ~0, at 537k about 1 (i.e. one unlucky domain gets over-blocked). Dropping to 32 bits would save 20% of the flash but cost ~7 collisions at 250k; going to 64 bits wastes 3 bytes per domain to solve a problem you don't have.
The same trick works on bigger chips — it isn't a C3 workaround. On a 16 MB ESP32-S3 these hashes hold ~2.7M domains vs ~466k for strings in 8 MB of PSRAM. Hashes in flash beat strings in PSRAM basically everywhere; the C3 just makes it undeniable.
