[Widget] Show first message in text mode for Text & Voice agents

[giannagerton]

Summary

Fixes ACF-55
Slack thread

conversation.tsx drops the first message for any text conversation that has a first_message configured, since it arrives after the user's opening message and would render out of order. Sheet compensated by rendering it locally — but only for agents configured text-only, so Text & Voice agents got neither copy.

Sheet now renders the local copy for any agent that supports text mode and has the text input enabled: as a preview before connecting, and through a text conversation. Voice conversations are untouched.

Behavior (text input turned on, transcript off)

Before no first message when opening the widget via the chat button

After first message shows, ability to switch to voice

[cursor]

PR Summary

Low Risk
UI-only transcript preview logic in the widget sheet; no auth, session, or server protocol changes. Layout of the open-but-disconnected sheet shifts because the transcript is no longer empty.

Overview
Text & Voice agents now show the locally rendered welcome message in text mode (preview and chat), not only text-only widgets. The server first message is still dropped in text conversations because it arrives after the user’s opener; voice calls keep the server copy so it is never duplicated.

The local copy also shows first-message rich content (e.g. greeting buttons) and strips TTS audio tags when strip_audio_tags is on. Opening the disconnected sheet with a greeting now has a non-empty transcript, so the compact layout (corner avatar, call button in the action row, resize) appears immediately.

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[cursor]

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[kamilk-11]

Nice!