content.Chunk is the sealed in-memory vocabulary for incremental output. Chunks are not serialized by core and do not have a wire tag; a provider stream decoder creates them from frames.

API surface

type Chunk interface{ isChunk() }

type TextChunk struct{ Text string }

type ThinkingChunk struct {
	Thinking  string
	Signature string
}

type ToolUseChunk struct {
	Index     int
	ID        string
	Name      string
	InputJSON string
}

Variant	Delta semantics
`TextChunk`	Append `Text` to the answer buffer
`ThinkingChunk`	Append `Thinking`; retain a non-empty terminal `Signature`
`ToolUseChunk`	Accumulate `InputJSON` by `Index`; ID and name may arrive later

switch typed := chunk.(type) {
case *content.TextChunk:
	answer.WriteString(typed.Text)
case *content.ThinkingChunk:
	reasoning.WriteString(typed.Thinking)
case *content.ToolUseChunk:
	toolParts.Add(typed)
}

Complete blocks have different ownership and fields. Use streamaccumulator to fold chunks into TextBlock, ThinkingBlock, and ToolUseBlock values.