[yuma2024]

Why

An app sometimes collects context before the chat starts (e.g. a form) and wants the AI to use it for the whole conversation without showing it in the chat. The existing inputs don't cover this: useAI({ prompt }) state, even when read from chat metadata, goes into the system prompt for the current run only. It is not part of the chat history and is not tied to a message. forwardedProps don't reach the model's messages. transformed_file is also sent but not shown, but the server prefixes it with a file header and it needs originalFile. What's needed is text attached to a message that stays in the history.

Change

• SendMessageOptions.hiddenText?: string. It is sent as a text part before the visible text and the attachments. No heading or separator is added. Whitespace-only hiddenText is ignored.
• Saved on the user message as a new PersistedHiddenTextContent ({ type: 'hidden_text', text }) part, so later turns and reloads send it again (transformMessagesToClientFormat).
• getDisplayTextFromContent only reads text parts, so the built-in bubble, chat title, chat list and save-as-command leave it out. Existing stored messages are read as before.
• Without hiddenText, behavior is unchanged. Client only; no server or core change.
• README: an example under Programmatic Chat Control, and a note that a custom Message slot should skip hidden_text parts.

API: additive. PersistedContentPart gains hidden_text, so a consumer with an exhaustive switch over it needs one more case (same as when transformed_file and attachment_ref were added). sendFn in UseMessageQueueOptions gains a 4th optional parameter rather than an options object, since that type is exported.

Tests

bun run test: client 580, server 370, workflows 27 pass. New tests: wire order and stored order (hidden → visible → attachments), chat title, the rendered user bubble, and that the text reaches the AI on a later turn after a reload. The bubble test fails if getDisplayTextFromContent picks up every part that has text; the reload test fails with the messageConversion.ts change reverted.

Not covered

• A long hiddenText is stored in localStorage like any other message text, so when storage is full the save can fail silently (same as long messages today). The AI then gets it only while the chat stays open, not after a reload, a reconnect or a chat switch.

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