Core Generate And Stream Text

Operator passes both `prompt: 'summarize this'` and `messages: [{role:'user', content:'hi'}]` to generateText, expecting messages to win.

Pass either `prompt` (shorthand single-user-turn) or `messages` (multi-turn) but not both — per docs they are mutually exclusive and the SDK throws InvalidArgumentError. Pick one and migrate the other content into it.

User closes the browser tab mid-stream; the Next.js route handler's request.signal aborts. streamText was called with abortSignal:request.signal.

Propagating request.signal to streamText closes the upstream provider HTTP connection so generation stops and billing for remaining tokens halts (per provider). Verify by reading onFinish.usage and confirming finishReason indicates cancellation rather than a full completion.

Operator places system instructions as `messages[0] = { role:'system', content:'You are a helpful assistant.' }` and also passes `system: 'Be concise.'` to streamText.

Pass system instructions via the top-level `system` parameter — the SDK merges it as the leading system message. Do not duplicate by also placing a system role in messages[]: providers either reject duplicates (Anthropic) or concatenate them in undefined order. Pick one location.