ThinkingBlock carries model reasoning text and the terminal signature or opaque provider state needed for replay. Thinking text can arrive before its signature during streaming.

API surface

type ThinkingBlock struct {
	Thinking            string
	Signature           string
	ProviderState       json.RawMessage
	ProviderStateFormat string
}

func NewThinkingBlock(thinking, signature string, providerState json.RawMessage, providerStateFormat string) *ThinkingBlock
func (b *ThinkingBlock) ReplayableAs(format string) bool

Field	Contract
`Thinking`	Reasoning text accumulated from deltas
`Signature`	Empty while streaming; provider signature on a complete block
`ProviderState`	Opaque JSON state for replay, never interpreted by core
`ProviderStateFormat`	Exact dialect label that owns `ProviderState`

NewThinkingBlock defensively copies the raw provider state. ReplayableAs returns false for a nil receiver, empty state, or a format mismatch. A codec must treat false as absent state; bytes from one provider must not be translated into another provider’s wire field.

Example

package main

import (
	"encoding/json"
	"fmt"

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

func main() {
	state := json.RawMessage(`{"signature":"opaque"}`)
	block := content.NewThinkingBlock("check the facts", "sig", state, "gemini")
	fmt.Println(block.ReplayableAs("gemini"), block.ReplayableAs("openai-responses"))
}

The zero signature is not an error during streaming. Use Thinking deltas and the core stream accumulator to produce a completed block.

Proof

Source: core/content/block.go
Tests: core/content/block_test.go, core/content/block_json_test.go

Related: Thinking deltas, AIMessage.