When a BlueBubbles inbound webhook arrives without `chatGuid`, processMessage
falls back to `resolveChatGuidForTarget` to look it up. The previous fallback
target was:
isGroup && (chatId || chatIdentifier)
? <chat_id or chat_identifier>
: { kind: "handle", address: message.senderId }
That `else` branch quietly covered two very different cases:
1. DM with no chatGuid — resolving via sender handle is correct, the chat
IS the conversation with that handle.
2. **Group with no chatGuid AND no chatId AND no chatIdentifier** — resolving
via sender handle yields *that sender's DM chatGuid*, then the rest of
processMessage uses it for ack reactions, mark-read, outbound reply cache,
typing indicators, and outboundTarget.
Case 2 is reachable: `monitor.webhook.test-helpers.ts` ships a default
`createMessageReactionPayloadForTest` payload with no chatGuid/chatId/
chatIdentifier and `isGroup` defaulted to `false`, mirroring real BlueBubbles
reaction/tapback webhooks. When a group reaction or tapback arrives in that
shape and isGroup is later corrected to true (or the message takes the same
poisoned path), `chatGuidForActions` becomes the sender's DM chatGuid. The
poisoned chatGuid then writes the outbound reply cache (line ~1395) with the
wrong chat, defeating the cross-chat short-id guard added in
9912472289 — a later short id resolved against that cache cannot detect the
mismatch and the agent's reaction/reply silently lands in the DM.
Symptom Chris observed (recurring after 9912472289 baked): group messages
getting reacted to from the agent's side show up in a DM transcript with
that sender, attached to a message GUID the user can no longer locate in
the DM.
Extract the fallback target construction into
`buildBlueBubblesInboundChatResolveTarget` so the rule is testable in
isolation and the wrong fallback can never be reached again:
- Group inbound + chatId present → `chat_id`
- Group inbound + chatIdentifier present → `chat_identifier`
- **Group inbound + neither → return null (caller skips chatGuid-dependent actions)**
- DM inbound → `handle` (unchanged: the conversation IS that sender)
processMessage now logs at verbose when the group case returns null instead
of silently degrading to the sender's DM.
Tests: extensions/bluebubbles/src/monitor-processing-chat-resolve.test.ts
covers the eight branches (group with id, group with identifier, group
preferring id, group with neither, blank/non-finite/null variants, DM, DM
with chat_id present, DM with empty sender).
Local patch for upstream consideration — pairs with the short-id chat guard
landed in the previous commit.
Chris Zhang
4bd3d258cd