feat(chat): resolve message capabilities and stage edits optimistically - #1392
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Groundwork for editing and deleting chat messages. No UI yet. Two seams, both in `:apps:flipcash:shared:chat`: `resolveCapabilities` answers what the viewer may do to a message — copy, reply, edit, delete — from the message and a `MessagePolicy`. Call sites read the set; they do not re-derive it. Group roles become another argument here rather than another branch at each menu. Cash is deliberately neither editable nor deletable, and an unconfirmed message resolves to nothing because `expected_event_sequence` is validated `>= 1`, so no valid request can be built for one. `PendingMutation` is the overlay shown between sending a mutation and the server answering. It lives in memory, never in the database, so a rollback is dropping a map entry rather than a compensating write. `ChatMessage.applying` retires an overlay as soon as the stored row carries a higher `eventSequence`, which lets `MessagingDelegate` persist the server's answer before it drops the overlay without flashing the pre-edit text in between. A conflict does not retry. The edit was written against a version that no longer exists, so re-applying it would clobber whoever got there first; instead the message is re-read and stored, and the caller is left to tell the user. Transport was already in place — `ChatMessagingController.editMessage` and `deleteMessage`, the `Deleted` content type, and the `event_sequence` and `last_edited_ts_epoch_ms` columns all exist. No proto or schema change.
This was referenced Sep 2, 2026
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Editing and deleting a chat message need three things the Android transcript did not have: a single
answer to what the viewer may do to a message, a way to show the result before the server confirms
it, and a mutation path on the coordinator. This adds all three; nothing calls them yet.
resolveCapabilitiesis the one place edit and delete availability is decided. It takes the messageand a
MessagePolicy(today just the edit window) and returns aSet<MessageCapability>. Grouproles, when they arrive, become another input to that function rather than another branch at every
menu site — which is why the policy is a parameter and not a constant.
PendingMutationis the optimistic overlay.ChatMessage.applying(mutation)returns the message asthe user should already see it, and it no-ops once
eventSequencehas moved past the sequence themutation was staged against, so a server update that has already landed wins over a stale local one.
MessagingDelegatestages a mutation before the RPC, reconciles it against the response, and dropsit on failure, so a rejected edit rolls back to the stored text rather than sticking.
The RPCs and the storage this needs were already in place —
Deletedcontent,event_sequenceandlast_edited_ts_epoch_msall exist in the published contract package and in Room — so there is noproto or migration change here.
Rules the tests pin down:
eventSequence == 0) offers nothing until it lands