Inbound message anatomy | Astropods

An incoming message is a Message. The same shape applies whether it came from Slack, the web chat, or any other adapter.

Node

Python

Message

Field	Type	Required	Notes
`id`	string	yes	UUID assigned by the sidecar.
`timestamp`	`Timestamp`	yes	When the platform received the message.
`platform`	string	yes	`"slack"`, `"web"`, `"discord"`, etc.
`platformContext`	`PlatformContext`	yes	Platform-native IDs and event metadata.
`user`	`User`	yes	Sender identity.
`content`	string	yes	Cleaned text. Adapters strip the bot’s @-mention before forwarding.
`attachments`	`Attachment[]`	no	Files, images, video, audio, link previews.
`conversationId`	string	yes	Stable correlation ID across the message lifecycle. Always echo back on responses.
`history`	`ConversationHistory`	no	Set when the earlier turns differ from what the agent last answered. See Edited messages. `null` otherwise.

ConversationHistory

Field	Type	Notes
`messages`	`HistoryMessage[]`	The turns before this message, oldest first. Can be empty.
`isComplete`	boolean	`false` when older turns were left out to bound the size.

HistoryMessage

Field	Type	Notes
`id`	string	Message ID in the chat.
`role`	string	`"user"` or `"assistant"`.
`content`	string	Text only. No attachments.

Timestamp (google.protobuf.Timestamp)

Field	Type	Notes
`seconds`	string	Seconds since UNIX epoch. Encoded as a string (can exceed JS safe int).
`nanos`	number	Nanoseconds within the second.

User

Field	Type	Required	Notes
`id`	string	yes	Platform-specific user ID.
`username`	string	no	Display name or handle.
`avatarUrl`	string	no	Avatar URL.
`email`	string	no	Email if available.
`userData`	`{ [key: string]: string }`	no	Platform-specific extras (workspace, role, etc.).

Attachment

Field	Type	Required	Notes
`type`	string	yes	One of the enum values below.
`url`	string	no	Download URL when the source provides one. Filesystem-backed web uploads leave this empty.
`filename`	string	no	Original filename.
`sizeBytes`	number	no	File size in bytes.
`mimeType`	string	no	MIME type.
`title`	string	no	Display title (rich attachments).
`description`	string	no	Display description.
`width`	number	no	For images/videos.
`height`	number	no	For images/videos.
`storageKey`	string	no	Opaque Files API key for a web-chat upload. Resolve it through `AGENT_FILES_DIR`; never construct an input path from `filename`.

Attachment.type values: TYPE_UNSPECIFIED, IMAGE, FILE, VIDEO, AUDIO, LINK.

PlatformContext

Field	Type	Required	Notes
`messageId`	string	yes	Original platform message ID.
`channelId`	string	yes	Channel/room/chat ID.
`threadId`	string	no	Agent’s reply target. Also set on top-level messages whose response should open a new thread.
`threadRootId`	string	no	Parent thread root timestamp. Set only when this message is a reply inside an existing thread.
`channelName`	string	no	Display channel name.
`workspaceId`	string	no	Slack workspace, Discord guild, etc.
`botUserId`	string	no	The bot’s own user ID in the source platform.
`userId`	string	no	Raw platform-native sender ID before any cross-platform identity resolution.
`eventKind`	string	yes	See `PlatformContextEventKind` below.
`platformData`	`{ [key: string]: string }`	no	Platform-specific extras (Slack `ts`, Discord snowflake, Teams activity ID).

PlatformContextEventKind

Value	When the adapter emits it
`EVENT_KIND_UNSPECIFIED`	Fallback. Should not appear in production traffic.
`EVENT_KIND_DM`	1:1 / private chat (Slack DM, web chat session).
`EVENT_KIND_APP_MENTION`	Bot was @-mentioned in a channel or thread.
`EVENT_KIND_THREAD_REPLY`	Reply inside an existing thread, no @-mention.
`EVENT_KIND_OBSERVED`	Observe-channel forward (listen-only).
`EVENT_KIND_REACTION`	Reaction added/removed.
`EVENT_KIND_BUTTON_CLICK`	Interactive button click on a `CardAttachment`.
`EVENT_KIND_SLASH_COMMAND`	Slash command (Slack/Discord).
`EVENT_KIND_ASSISTANT_THREAD_STARTED`	Slack assistant thread opened.

Edited messages

In the web chat, a user can edit a message they sent. The chat keeps the old message and its replies as another version, and the user can switch between versions. The history your agent stores for the conversation then holds turns the user replaced.

When that happens, the next message carries history: the turns before it, on the version the user is looking at. Replace the history you store for conversationId with history, then handle the message as usual. An empty history means the message has no earlier turns, as when the user edits their first message. The same field arrives when the user switches to another version and continues there, and after a turn your agent did not answer.

history carries text only; a user turn that carried only files arrives as a line naming them. It holds the newest turns that fit in 512 KiB, and isComplete is false when it left older ones out.

The chat offers editing only for agents that set supportsHistory in the config they send at startup. The Mastra and LangChain adapters and the AI SDK adapter set it and reset their memory for you. In your own adapter the flag defaults to off, so an agent that ignores history never receives an edit.

Node.js

Python

getConfig() {
  return { systemPrompt: "You are a helpful assistant.", tools: [], supportsHistory: true };
}

For web-chat file input and agent-produced downloads, see Files in chat.

Next steps

Sending a response: reply to what arrived
Receiving platform feedback: reactions, edits, and stream control