Watch-history decryption previously ordered the matching cipher family
first but kept the other family as a *fallback*. The opposite family can
never decrypt a given ciphertext (NIP-04 always carries a literal "?iv="
marker; NIP-44 is plain base64), so that fallback was a guaranteed-wasted
decrypt attempt. Under a NIP-46 remote signer every decrypt is a
*published* relay RPC routed through the serial 250ms request queue, so a
transient failure on the correct family triggered a second wasted RPC
that burned the queue and pushed cold loads toward the relay rate limit
("noting too much") — the symptom users hit.
determineWatchHistoryDecryptionOrder now filters the attempt set to the
single family implied by the ciphertext shape (trusting the ciphertext
over a possibly-misleading "encrypted" tag), with a safety fallback to
the full ordered list when nothing matches so the only available
decryptor is never stranded. This mirrors the list-decrypt routing
already shipped for userBlocks / subscriptions / hashtags (slice A).
Test: a NIP-44 ciphertext mislabeled with an ["encrypted","nip04"] tag,
against a signer exposing both decryptors where nip04 returns decoy data.
Asserts nip04 is never attempted and the nip44 plaintext is used.
Mutation-verified: removing the filter fails the test.
Co-Authored-By: Claude Opus 4.8 <[email protected]>
