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The browser Chat target for Conversation assembly. It registers Chat event definitions and snapshot construction, supplies useChat, renders transcript nodes and details, and owns Chat-specific stores, actions, localization, and scroll restoration; historical image URLs resolve through the Conversation-owned per-session cache (ctx.uiConversation.imageUrl). Its Assistant and Turn Tail definitions fold packed historical Assistant runs without expanding their members.
Chat contributes a System prompt row for a non-empty initial or resumed request, an explicit series start, or an actual system-field change; same-series config-only or tool-only changes, tool steps, and retries do not duplicate it. Chat places the first header in a step at that request's message boundary — turn start for step one, step start thereafter — before the user-role messages sent with the request, matching the provider envelope's system-before-messages order; when the preceding header is outside a partial window, a non-initial header stays at its own Event and renders conservatively until prepend supplies that predecessor. The row stays collapsed by default and mounts the complete prompt in the same 141px code-block body as an opaque context injection — model-facing text with its real line breaks, not Markdown — only while expanded; it has no streaming path. Systemless headers produce no row.
None, as this package renders logged conversation state in the browser and registers nothing model-facing.
None; Chat presentation does not assemble or mutate provider requests.
turn/start and every started model attempt has safe, exact usage. Missing buckets are omitted, and incomplete or contradictory accounting hides the whole disclosure.