feat(slack): add threadDirectMessages option

[dancer]

summary

adds threadDirectMessages to SlackAdapterConfig. when enabled, a top-level DM becomes its own thread root and the bot replies inside that thread, instead of every message and reply landing in one flat DM transcript

const slack = createSlackAdapter({ threadDirectMessages: true })

it also gives DMs the thread_ts that slack's native streaming api requires. chat.startStream documents thread_ts as required, and the adapter's stream() returns null on an empty threadTs, so a flat DM could never stream natively and always fell back to post-and-edit. threaded DMs stream natively, which is the gap described in #503

agentView already threaded DMs, but only as part of the full agents setup (manifest agent_view, assistant:write, chat tab). that behavior is now available on its own, and agentView implies it

behavior

	thread id	reply
default	slack:D123:	flat in the DM
threadDirectMessages: true	slack:D123:{ts}	in a thread under the user's message

defaults to false. thread ids are storage keys, so flipping the default would orphan existing subscriptions and per-thread state for every deployed slack bot

subscriptions keep working. the existing openDM() bridge is reused, so when the conversation-scoped thread is subscribed, top-level DMs still route to it and onSubscribedMessage and proactive flows are unaffected

channels are untouched

implementation

the two agentView gates in handleMessageEvent now read a combined dmThreading flag:

this.dmThreading = this.agentView || (config.threadDirectMessages ?? false)

const threadTs =
  isDM && !this.dmThreading
    ? event.thread_ts || ""
    : event.thread_ts || event.ts

the remaining agentView checks (app_home tab handling, suggested prompts) are agents-ui concerns and stay as they are

test plan

• a top-level DM threads under its own ts when the option is on
• DM replies stay on the parent thread_ts
• a top-level DM routes to the conversation-scoped thread when it is subscribed, covering the openDM() flow
• DMs stay conversation-scoped when the option is unset
• channel threading is unchanged

verified against a real slack workspace over socket mode, on a non-agent app so message.im arrives with no thread_ts:

• conversations.replies shows the user's own message as the thread root (thread_ts == ts) with the bot reply inside it
• conversations.history shows only user messages at top level with reply_count: 1, so bot replies no longer sit in the flat DM
• native streaming engages in a DM, logging chat.startStream with the incoming message ts and no post-and-edit fallback
• with the option off, the same DM resolves to slack:D...: and the reply lands flat

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Project	Deployment	Actions	Updated (UTC)
chat	Ready	Preview, v0	Aug 3, 2026 11:44am
chat-sdk-nextjs-chat	Ready	Preview	Aug 3, 2026 11:44am