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Two events published in the same second reliably lose one of them. The receiver stores the kind:445 and produces nothing from it -- no inner event, no chat line, no error anybody sees, because MarmotGroupEvent is written before the message is decrypted and so survives while everything downstream silently does not. Observed as a FROST signing session that never started on the receiver: proposeSigning publishes the proposal and then the proposer's own nonce, the relay handed them back in the other order, and the proposal was dropped. The nonce is still sitting there filed against a session that will never exist. The same bug ate a dialect earlier, which then took out the artifact referencing it via a foreign key. MLS is specified to tolerate this. RFC 9420 says a receiver that gets generation N+1 before N keeps the intermediate keys so the older message can still be read, and quartz's SecretTree does exactly that, in a private skippedKeys map. What it does not do is persist it: exportSenderStates() returns the ratchet positions only, so saveState() drops the cache. NostrDao rebuilt the group from stored state for every inbound event, so the cache was empty every single time, and generation N arriving after N+1 failed `require(generation >= applicationGeneration)` and was swallowed. Terminal -- the key is derived from a ratchet that has moved past it, and nothing asks the sender to resend. This keeps the instance alive instead. MlsGroupCache holds one MlsGroup per room, and the inbound path goes through it, so skippedKeys survives from one message to the next. That covers the case that actually bites -- a burst arriving in one sync, decrypted one after another against the same tree -- which is what every bursty flow needs: proposeRitual sends two, addArtifact sends two, and addChapter sends one per paragraph plus one, of which only the ones arriving in ascending generation order survived. Reuse is conditional on the stored state still being exactly what the cache last wrote. Sending a message advances the sender ratchet and saves; so does adding a member. When that happens the cache rebuilds rather than carrying on from a group that has been overtaken -- which is what keeps this from being worse than no cache at all: the fallback is always the old behaviour, never a diverged ratchet. One lock per room, not one overall, because the group is mutable and decryption advances it: two events for the same room decrypted at once would corrupt the tree, and a busy room should not hold up a quiet one. **This is a mitigation, not the fix.** It does not survive a restart, and it does not survive another writer, so a long enough reorder still loses the message. The fix belongs in quartz -- carry skippedKeys through saveState/restore -- and quartz is a mavenCentral binary, not a fork, so it cannot be made here. docs/mls-skipped-keys.md has the analysis, the patch, the migration constraint on the persisted state format, and the three ways to actually land it. Not verified end to end: the proposal that exposed this cannot be recovered, since its generation is already past, so confirming the fix needs a fresh burst. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
mantra docs
Notes on the parts of this app whose behaviour is not recoverable by reading the code alone — where the reasoning lives in a protocol, a failure mode that is silent, or a decision that looked arbitrary and was not.
| document | covers |
|---|---|
| shared-key-ceremony.md | ChillDKG over NIP-17: the rounds, the approval gates, the chat transcript, participant ordering |
| shared-key-derivation.md | deriving further keys from the group's threshold key with FROST tweaks — why not BIP32, why no chain code, and the one rule that must not be broken |
| marmot-membership.md | how members join an MLS group, and the epoch race that makes a missing member look like a successful invite |
| mls-skipped-keys.md | why a group event that arrives a moment late is dropped for good, which flows trigger it, the quartz fix, and the partial mitigation in this app |
Start with the ceremony if you are new to this area; the other two both assume it. Read the skipped-keys note before debugging any "the other device never got it" report — it is silent, and it looks like every other kind of delivery failure.