feat(chat): add message update and delete lifecycle callbacks

[dancer]

summary

adds onMessageUpdated and onMessageDeleted, so a bot can react when a message is edited or removed. Slack dispatches both today; other adapters can opt in later

supersedes #549, which was verified there against real Slack webhooks. reopened from a branch in this repo with the original commits preserved and signed

bot.onMessageUpdated(async (thread, message, previousMessage) => {
  await mirror.update(message.id, message.text);
});

bot.onMessageDeleted(async (event) => {
  await mirror.remove(event.messageId);
});

both are lifecycle events: they never route through onNewMessage, onNewMention, or onSubscribedMessage, and the concurrency strategies do not apply

notes

• the bot's own edits are filtered. slack sends a message_changed for every chat.update, and post-and-edit streaming calls it once per delta, so without this a single streamed reply would call the handler back repeatedly on its own message
• previousMessage is forwarded on edits. slack sends the pre-edit message and it was being dropped. an edit handler usually needs the before to know what changed, so it is the optional third argument
• the two shapes differ deliberately. an edit carries a full replacement message, so it gets (thread, message, previousMessage?). a delete has no message, only the id of what was removed, so it gets an event. use chat.thread(event.threadId) when a delete handler needs one
• one thread id helper now serves message, edit, and delete, so an edit cannot resolve to a different thread than the message it edits

test plan

core:

• an edit dispatches to onMessageUpdated and not to the normal message handlers
• the handler receives the pre-edit message as its third argument
• the bot's own edits are skipped
• a delete dispatches with normalized event data
• both run inside the active conversation, so read tools built in these handlers stay scoped

slack:

• message_changed dispatches as an update, message_deleted as a delete
• previous_message is forwarded, and left undefined when slack omits it
• hidden unfurl updates stay ignored, hidden real edits still dispatch
• message, edit, and delete resolve to one thread id in a flat DM and in a threaded agent_view DM

verified against a real slack workspace over socket mode: editing and deleting a DM both routed to the same thread id as the original message

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Project	Deployment	Actions	Updated (UTC)
chat	Ready	Preview, v0	Aug 5, 2026 12:15pm
chat-sdk-nextjs-chat	Ready	Preview	Aug 5, 2026 12:15pm