Looprig represents model input and output as an ordered slice of sealed content.Block values. The concrete Go pointer is the in-memory discriminator; JSON adds a type tag at the boundary. This keeps provider codecs independent of ad-hoc maps while still allowing nested tool results.

The block vocabulary

Variant	Payload	Typical direction
`TextBlock`	UTF-8 text	input or output
`ImageBlock`	MIME type plus URL or bytes	input
`AudioBlock`	MIME type plus bytes	input
`DocumentBlock`	MIME type, name, bytes, or extracted text	input
`ThinkingBlock`	reasoning text, signature, provider state	output and replay
`ToolUseBlock`	call ID, name, raw JSON arguments	output
`ToolResultBlock`	tool-call ID, nested blocks, error bit	input

package main

import (
	"encoding/json"
	"fmt"

	"github.com/looprig/core/content"
)

func main() {
	blocks := []content.Block{
		&content.TextBlock{Text: "Inspect this report."},
		&content.ToolUseBlock{
			ID: "call-1", Name: "search",
			Input: json.RawMessage(`{"query":"revenue"}`),
		},
	}
	wire, err := content.MarshalBlocks(blocks)
	if err != nil {
		panic(err)
	}
	decoded, err := content.UnmarshalBlocks(wire)
	if err != nil {
		panic(err)
	}
	fmt.Printf("%T %T\n", decoded[0], decoded[1])
}

The block interface is sealed by an unexported isBlock method. A consumer should type-switch over the seven exported pointer variants and treat an unexpected or typed-nil value as invalid input.

Blocks and streaming chunks

Complete blocks and incremental chunks are intentionally different types. A TextChunk contains a delta; a TextBlock contains the assembled value. Thinking signatures and tool-call argument fragments are the reason the distinction matters.

%%{init: {"theme":"base","themeVariables":{"background":"#111827","primaryColor":"#1f2937","primaryTextColor":"#f8fafc","primaryBorderColor":"#64748b","lineColor":"#94a3b8","secondaryColor":"#0f172a","tertiaryColor":"#172033","fontFamily":"Inter, ui-sans-serif, system-ui, sans-serif"}}}%%
flowchart LR
    wire[Provider stream] --> chunk[content.Chunk]
    chunk --> fold[streamaccumulator]
    fold --> block[content.Block]
    block --> message[AIMessage]
    classDef dark fill:#1f2937,stroke:#94a3b8,color:#f8fafc
    class wire,chunk,fold,block,message dark

Proof

Source: core/content/block.go, core/content/chunk.go
Tests: core/content/block_test.go, core/content/block_json_test.go
Example: core/examples/content/example_test.go

Related: Messages, Streaming, ToolUseBlock.