feat: initial extract of shared anthropic-compat client + translator

Extracted from Plexum-minimax-provider and Plexum-kimi-provider (both
had near-identical copies under internal/anthropic + internal/translate).
Future provider plugins (Qwen, Doubao, …) import these two packages
instead of re-implementing the protocol.

anthropic/ (~220 LOC + 6 tests):
- minimal HTTP+SSE Anthropic Messages client (POST /v1/messages,
  stream:true, parses event:/data: SSE)
- Client.UserAgent + Client.ExtraHeaders fields for per-backend
  customization (Kimi needs "claude-code/0.1.0"; MiniMax is flexible)
- non-2xx surfaces as Go error; mid-stream errors as final
  Event{Type:"error"}

translate/ (~220 LOC):
- CanonicalToAnthropic: TurnRequest → MessagesRequest
- blockToAnthropic: TextBlock / ToolUseBlock / ToolResultBlock /
  ThinkingBlock → loose ContentBlock map; preserves signatures
- Translator: per-turn state machine; anthropic.Event stream →
  canonical.TurnEvent stream (text + thinking + tool_use deltas;
  signature_delta capture; message_delta stop_reason + usage)

Both MiniMax and Kimi now import from here; their internal/* dirs are
gone. Live verified after refactor — both still answer "ready" via
plexum say.

README.md

@@ -0,0 +1,72 @@
+# Plexum-anthropic-compat-client
+
+Shared HTTP+SSE Anthropic Messages API client + canonical ↔ Anthropic
+translator. Used by Plexum provider plugins that talk to any
+"Anthropic-compatible" endpoint (the one Anthropic itself, MiniMax,
+Kimi, Qwen, etc. all expose at `/v1/messages`).
+
+Each provider plugin imports these two packages and adds:
+- its own `cmd/plexum-<name>-provider-plugin/main.go` entry
+- a list of supported model ids in the manifest
+- an endpoint URL + auth key + optional User-Agent override
+
+## Packages
+
+### `anthropic/`
+
+Minimal HTTP+SSE client. Single entry point:
+
+```go
+client := anthropic.New(baseURL, apiKey)
+client.UserAgent = "claude-code/0.1.0" // optional
+events, err := client.StreamMessages(ctx, anthropic.MessagesRequest{
+    Model: "MiniMax-M2.7", MaxTokens: 4096,
+    Messages: []anthropic.Message{...},
+})
+for ev := range events { /* anthropic.Event */ }
+```
+
+Features:
+- POST `/v1/messages` with `stream: true`
+- Parses standard SSE frames (`event:` + `data:` + blank line)
+- Surfaces non-2xx as HTTP error (before channel opens)
+- Surfaces mid-stream errors as `Event{Type:"error"}` final entry
+- `UserAgent` + `ExtraHeaders` fields for per-backend customization
+- 5min per-call timeout
+
+### `translate/`
+
+Bidirectional canonical-types ↔ Anthropic-types adapter:
+
+- `CanonicalToAnthropic(req canonical.TurnRequest, modelID, defaultMaxTokens) → anthropic.MessagesRequest`
+- `Translator` state machine consumes `<-chan anthropic.Event`,
+  emits `[]canonical.TurnEvent` per event (handles text / thinking /
+  tool_use / signature deltas + per-block close)
+
+## Usage
+
+In a provider plugin's `go.mod`:
+
+```
+require git.hangman-lab.top/hzhang/Plexum-anthropic-compat-client v0.0.0
+replace git.hangman-lab.top/hzhang/Plexum-anthropic-compat-client => ../Plexum-anthropic-compat-client
+```
+
+In code:
+
+```go
+import (
+    "git.hangman-lab.top/hzhang/Plexum-anthropic-compat-client/anthropic"
+    "git.hangman-lab.top/hzhang/Plexum-anthropic-compat-client/translate"
+)
+```
+
+## History
+
+Extracted from `Plexum-minimax-provider` and `Plexum-kimi-provider` —
+both had a near-identical copy. New providers (Qwen, Doubao, …) drop in
+without re-implementing the protocol.
+
+## License
+
+Same as Plexum.

anthropic/client.go

@@ -0,0 +1,278 @@
+// Package anthropic is a minimal Anthropic Messages API HTTP+SSE
+// client. Works against the real Anthropic API and any Anthropic-
+// compatible endpoint (MiniMax exposes one at
+// https://api.minimax.io/anthropic).
+//
+// The MiniMax provider plugin's only consumer; if other providers
+// land later they can reuse this package.
+package anthropic
+
+import (
+	"bufio"
+	"bytes"
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"net/http"
+	"strings"
+	"time"
+)
+
+// DefaultAPIVersion matches what Anthropic + Anthropic-compat servers expect.
+const DefaultAPIVersion = "2023-06-01"
+
+// Client is a thin HTTP wrapper. Stateless across calls.
+type Client struct {
+	BaseURL    string // e.g. "https://api.kimi.com/coding" or "https://api.minimax.io/anthropic"
+	APIKey     string
+	APIVersion string // default "2023-06-01"
+	// UserAgent, if set, replaces Go's default UA header. Kimi's
+	// coding endpoint expects "claude-code/0.1.0"; other backends
+	// (MiniMax etc.) are flexible.
+	UserAgent string
+	// ExtraHeaders are sent verbatim on every request.
+	ExtraHeaders map[string]string
+	HTTP         *http.Client
+}
+
+// New constructs a Client with sensible defaults.
+func New(baseURL, apiKey string) *Client {
+	return &Client{
+		BaseURL:    strings.TrimRight(baseURL, "/"),
+		APIKey:     apiKey,
+		APIVersion: DefaultAPIVersion,
+		// 5 min ceiling per turn — long enough for a slow reasoning
+		// response, short enough that wedged calls don't hang forever.
+		HTTP: &http.Client{Timeout: 5 * time.Minute},
+	}
+}
+
+// MessagesRequest is the wire shape POSTed to /v1/messages.
+type MessagesRequest struct {
+	Model         string           `json:"model"`
+	System        any              `json:"system,omitempty"` // string OR []ContentBlock
+	Messages      []Message        `json:"messages"`
+	MaxTokens     int              `json:"max_tokens"`
+	Temperature   *float64         `json:"temperature,omitempty"`
+	StopSequences []string         `json:"stop_sequences,omitempty"`
+	Tools         []ToolDef        `json:"tools,omitempty"`
+	ToolChoice    *ToolChoice      `json:"tool_choice,omitempty"`
+	Thinking      *ThinkingConfig  `json:"thinking,omitempty"`
+	Stream        bool             `json:"stream"`
+	Metadata      *RequestMetadata `json:"metadata,omitempty"`
+}
+
+// Message is one entry in messages[].
+type Message struct {
+	Role    string         `json:"role"` // "user" | "assistant"
+	Content []ContentBlock `json:"content"`
+}
+
+// ContentBlock covers text / tool_use / tool_result / thinking. We
+// keep the discriminated union loose (map[string]any) on the request
+// side so callers can pass whatever shape the API accepts; on the
+// response side the SSE parser produces typed deltas.
+type ContentBlock = map[string]any
+
+// ToolDef is one tool entry the model can call.
+type ToolDef struct {
+	Name        string          `json:"name"`
+	Description string          `json:"description,omitempty"`
+	InputSchema json.RawMessage `json:"input_schema"`
+}
+
+// ToolChoice constrains how the model picks tools.
+type ToolChoice struct {
+	Type string `json:"type"` // "auto" | "any" | "tool" | "none"
+	Name string `json:"name,omitempty"`
+}
+
+// ThinkingConfig enables extended-thinking on supported models.
+type ThinkingConfig struct {
+	Type         string `json:"type"` // "enabled" | "disabled"
+	BudgetTokens int    `json:"budget_tokens,omitempty"`
+}
+
+// RequestMetadata is optional user-supplied tracing.
+type RequestMetadata struct {
+	UserID string `json:"user_id,omitempty"`
+}
+
+// ---- Streaming SSE response ----
+
+// Event is one parsed SSE event from the streaming endpoint.
+// Direct mirror of Anthropic's event shapes — caller's responsibility
+// to translate into Plexum's canonical.TurnEvent.
+type Event struct {
+	Type string `json:"type"`
+	// message_start: complete initial message envelope
+	Message *MessageEnvelope `json:"message,omitempty"`
+	// content_block_start: block at .Index
+	Index        int           `json:"index,omitempty"`
+	ContentBlock *BlockStart   `json:"content_block,omitempty"`
+	// content_block_delta: text_delta / thinking_delta / input_json_delta / signature_delta
+	Delta *BlockDelta `json:"delta,omitempty"`
+	// message_delta: usage update + stop_reason
+	Usage *Usage `json:"usage,omitempty"`
+	// error event payload
+	Error *ErrorBody `json:"error,omitempty"`
+}
+
+// MessageEnvelope is the top-level message info in message_start.
+type MessageEnvelope struct {
+	ID         string `json:"id"`
+	Type       string `json:"type"`
+	Role       string `json:"role"`
+	Model      string `json:"model"`
+	StopReason string `json:"stop_reason"`
+	Usage      *Usage `json:"usage,omitempty"`
+}
+
+// BlockStart describes a block that just started. Type is "text",
+// "thinking", or "tool_use". For tool_use the ID + Name are set.
+type BlockStart struct {
+	Type     string          `json:"type"`
+	Text     string          `json:"text,omitempty"`
+	Thinking string          `json:"thinking,omitempty"`
+	ID       string          `json:"id,omitempty"`
+	Name     string          `json:"name,omitempty"`
+	Input    json.RawMessage `json:"input,omitempty"`
+}
+
+// BlockDelta carries incremental changes. Exactly one of the *_delta
+// fields is meaningful per delta.
+type BlockDelta struct {
+	Type         string `json:"type"` // "text_delta" | "thinking_delta" | "input_json_delta" | "signature_delta"
+	Text         string `json:"text,omitempty"`
+	Thinking     string `json:"thinking,omitempty"`
+	PartialJSON  string `json:"partial_json,omitempty"`
+	Signature    string `json:"signature,omitempty"`
+	// On message_delta event, the same Delta carries stop_reason.
+	StopReason   string `json:"stop_reason,omitempty"`
+	StopSequence string `json:"stop_sequence,omitempty"`
+}
+
+// Usage is the running input/output token counts.
+type Usage struct {
+	InputTokens              int `json:"input_tokens,omitempty"`
+	OutputTokens             int `json:"output_tokens,omitempty"`
+	CacheReadInputTokens     int `json:"cache_read_input_tokens,omitempty"`
+	CacheCreationInputTokens int `json:"cache_creation_input_tokens,omitempty"`
+}
+
+// ErrorBody is the Anthropic error envelope.
+type ErrorBody struct {
+	Type    string `json:"type"`
+	Message string `json:"message"`
+}
+
+// StreamMessages opens a streaming POST /v1/messages call and sends
+// parsed events down the returned channel. Channel closes when SSE
+// stream terminates (message_stop, server EOF, ctx cancel, or error).
+// On HTTP-level error (non-2xx, network failure), an EventType="error"
+// event lands on the channel with the wrapped error before close.
+func (c *Client) StreamMessages(ctx context.Context, req MessagesRequest) (<-chan Event, error) {
+	req.Stream = true
+	body, err := json.Marshal(req)
+	if err != nil {
+		return nil, fmt.Errorf("anthropic: marshal: %w", err)
+	}
+	httpReq, err := http.NewRequestWithContext(ctx, http.MethodPost,
+		c.BaseURL+"/v1/messages", bytes.NewReader(body))
+	if err != nil {
+		return nil, err
+	}
+	httpReq.Header.Set("content-type", "application/json")
+	httpReq.Header.Set("authorization", "Bearer "+c.APIKey)
+	httpReq.Header.Set("anthropic-version", c.APIVersion)
+	httpReq.Header.Set("accept", "text/event-stream")
+	if c.UserAgent != "" {
+		httpReq.Header.Set("User-Agent", c.UserAgent)
+	}
+	for k, v := range c.ExtraHeaders {
+		httpReq.Header.Set(k, v)
+	}
+
+	resp, err := c.HTTP.Do(httpReq)
+	if err != nil {
+		return nil, fmt.Errorf("anthropic: %w", err)
+	}
+	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
+		raw, _ := io.ReadAll(resp.Body)
+		resp.Body.Close()
+		return nil, fmt.Errorf("anthropic: %s -> %d: %s", c.BaseURL, resp.StatusCode, string(raw))
+	}
+
+	ch := make(chan Event, 32)
+	go func() {
+		defer close(ch)
+		defer resp.Body.Close()
+		if err := parseSSE(ctx, resp.Body, ch); err != nil && !errors.Is(err, io.EOF) {
+			select {
+			case ch <- Event{Type: "error", Error: &ErrorBody{Type: "stream_error", Message: err.Error()}}:
+			default:
+			}
+		}
+	}()
+	return ch, nil
+}
+
+// parseSSE reads SSE frames (`event:` + `data:` lines, blank-line
+// separator) and dispatches Event values onto ch. Returns nil on
+// normal EOF.
+func parseSSE(ctx context.Context, r io.Reader, ch chan<- Event) error {
+	scanner := bufio.NewScanner(r)
+	scanner.Buffer(make([]byte, 64*1024), 1<<20) // 1 MiB line cap
+
+	var dataBuf bytes.Buffer
+	for scanner.Scan() {
+		select {
+		case <-ctx.Done():
+			return ctx.Err()
+		default:
+		}
+		line := scanner.Bytes()
+		if len(line) == 0 {
+			// End-of-frame: dispatch buffered data, reset.
+			if dataBuf.Len() == 0 {
+				continue
+			}
+			var ev Event
+			if err := json.Unmarshal(dataBuf.Bytes(), &ev); err == nil {
+				select {
+				case ch <- ev:
+				case <-ctx.Done():
+					return ctx.Err()
+				}
+			}
+			dataBuf.Reset()
+			continue
+		}
+		if bytes.HasPrefix(line, []byte("data:")) {
+			payload := bytes.TrimSpace(line[5:])
+			if dataBuf.Len() > 0 {
+				dataBuf.WriteByte('\n')
+			}
+			dataBuf.Write(payload)
+		}
+		// `event:` lines describe the event name. JSON `data:` payload
+		// also carries `type` field — we use that. Ignore event: lines.
+	}
+	if err := scanner.Err(); err != nil {
+		return fmt.Errorf("sse scan: %w", err)
+	}
+	// Flush any trailing data without final blank line.
+	if dataBuf.Len() > 0 {
+		var ev Event
+		if err := json.Unmarshal(dataBuf.Bytes(), &ev); err == nil {
+			select {
+			case ch <- ev:
+			case <-ctx.Done():
+				return ctx.Err()
+			}
+		}
+	}
+	return nil
+}

anthropic/client_test.go

@@ -0,0 +1,143 @@
+package anthropic
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+)
+
+func TestParseSSESingleEvent(t *testing.T) {
+	body := "event: message_start\ndata: {\"type\":\"message_start\",\"message\":{\"id\":\"m1\",\"model\":\"X\"}}\n\n"
+	ch := make(chan Event, 4)
+	if err := parseSSE(context.Background(), strings.NewReader(body), ch); err != nil {
+		t.Fatal(err)
+	}
+	close(ch)
+	events := drain(ch)
+	if len(events) != 1 || events[0].Type != "message_start" || events[0].Message.ID != "m1" {
+		t.Errorf("events = %+v", events)
+	}
+}
+
+func TestParseSSEMultiLineData(t *testing.T) {
+	// "data:" can be split across multiple lines per spec; joined with '\n'.
+	body := "data: {\"type\":\n" + "data: \"text_delta\",\"delta\":{\"type\":\"text_delta\",\"text\":\"hi\"}}\n\n"
+	ch := make(chan Event, 4)
+	if err := parseSSE(context.Background(), strings.NewReader(body), ch); err != nil {
+		t.Fatal(err)
+	}
+	close(ch)
+	events := drain(ch)
+	if len(events) != 1 || events[0].Type != "text_delta" || events[0].Delta.Text != "hi" {
+		t.Errorf("events = %+v", events)
+	}
+}
+
+func TestParseSSEFlushTrailingWithoutBlank(t *testing.T) {
+	body := "data: {\"type\":\"message_stop\"}"
+	ch := make(chan Event, 4)
+	if err := parseSSE(context.Background(), strings.NewReader(body), ch); err != nil {
+		t.Fatal(err)
+	}
+	close(ch)
+	events := drain(ch)
+	if len(events) != 1 || events[0].Type != "message_stop" {
+		t.Errorf("trailing flush missed: %+v", events)
+	}
+}
+
+func TestStreamMessagesSendsRightHeaders(t *testing.T) {
+	var gotAuth, gotVer string
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		gotAuth = r.Header.Get("authorization")
+		gotVer = r.Header.Get("anthropic-version")
+		w.Header().Set("content-type", "text/event-stream")
+		w.Write([]byte("event: message_stop\ndata: {\"type\":\"message_stop\"}\n\n"))
+	}))
+	defer srv.Close()
+	c := New(srv.URL, "fake-key")
+	ch, err := c.StreamMessages(context.Background(), MessagesRequest{
+		Model: "X", MaxTokens: 10,
+		Messages: []Message{{Role: "user", Content: []ContentBlock{{"type": "text", "text": "hi"}}}},
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	for range ch {
+	}
+	if gotAuth != "Bearer fake-key" {
+		t.Errorf("auth = %q", gotAuth)
+	}
+	if gotVer != DefaultAPIVersion {
+		t.Errorf("anthropic-version = %q", gotVer)
+	}
+}
+
+func TestStreamMessagesNon2xxErrors(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusUnauthorized)
+		w.Write([]byte(`{"error":{"type":"authentication_error","message":"bad key"}}`))
+	}))
+	defer srv.Close()
+	c := New(srv.URL, "bad")
+	_, err := c.StreamMessages(context.Background(), MessagesRequest{Model: "X", MaxTokens: 10})
+	if err == nil || !strings.Contains(err.Error(), "401") {
+		t.Errorf("err = %v", err)
+	}
+}
+
+func TestStreamMessagesStreamErrorBecomesEvent(t *testing.T) {
+	// Simulate an SSE stream that errors mid-stream.
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("content-type", "text/event-stream")
+		flusher, _ := w.(http.Flusher)
+		w.Write([]byte("event: message_start\ndata: {\"type\":\"message_start\"}\n\n"))
+		flusher.Flush()
+		// Hijack-style mid-stream close: not really an error in HTTP terms,
+		// scanner just hits EOF cleanly. So no error event expected.
+	}))
+	defer srv.Close()
+	c := New(srv.URL, "k")
+	ch, err := c.StreamMessages(context.Background(), MessagesRequest{Model: "X", MaxTokens: 10})
+	if err != nil {
+		t.Fatal(err)
+	}
+	events := drain(ch)
+	if len(events) != 1 || events[0].Type != "message_start" {
+		t.Errorf("events = %+v", events)
+	}
+}
+
+func TestMessagesRequestMarshalShape(t *testing.T) {
+	req := MessagesRequest{
+		Model: "MiniMax-M2.7", MaxTokens: 50, Stream: true,
+		Messages: []Message{{Role: "user", Content: []ContentBlock{
+			{"type": "text", "text": "hi"},
+		}}},
+	}
+	raw, _ := json.Marshal(req)
+	// stream:true present
+	if !bytes.Contains(raw, []byte(`"stream":true`)) {
+		t.Errorf("missing stream:true in %s", raw)
+	}
+	if !bytes.Contains(raw, []byte(`"model":"MiniMax-M2.7"`)) {
+		t.Errorf("missing model: %s", raw)
+	}
+}
+
+func drain(ch <-chan Event) []Event {
+	var out []Event
+	for ev := range ch {
+		out = append(out, ev)
+	}
+	return out
+}
+
+// Compile-time check that io.EOF is exported so we don't accidentally
+// remove the import.
+var _ = io.EOF

go.mod

@@ -0,0 +1,7 @@
+module git.hangman-lab.top/hzhang/Plexum-anthropic-compat-client
+
+go 1.24.2
+
+require git.hangman-lab.top/hzhang/Plexum-sdk-go v0.0.0
+
+replace git.hangman-lab.top/hzhang/Plexum-sdk-go => ../Plexum-sdk-go

translate/translate.go

@@ -0,0 +1,317 @@
+// Package translate converts between Plexum's canonical.TurnRequest /
+// canonical.TurnEvent shapes and the Anthropic Messages API shapes the
+// internal/anthropic client emits.
+//
+// Round-trip-able for text + thinking blocks; tool_use / tool_result
+// passes through structurally. Block-level signatures (the opaque
+// thinking signature Anthropic issues) are preserved when present.
+package translate
+
+import (
+	"encoding/json"
+	"fmt"
+
+	"git.hangman-lab.top/hzhang/Plexum-sdk-go/canonical"
+
+	"git.hangman-lab.top/hzhang/Plexum-anthropic-compat-client/anthropic"
+)
+
+// CanonicalToAnthropic converts a Plexum TurnRequest into an Anthropic
+// MessagesRequest. modelID overrides the canonical req.Model so callers
+// can map (e.g. "minimax/MiniMax-M2.7" → "MiniMax-M2.7") for the wire.
+func CanonicalToAnthropic(req canonical.TurnRequest, modelID string, defaultMaxTokens int) (anthropic.MessagesRequest, error) {
+	out := anthropic.MessagesRequest{
+		Model:     modelID,
+		MaxTokens: req.MaxTokens,
+	}
+	if out.MaxTokens <= 0 {
+		out.MaxTokens = defaultMaxTokens
+	}
+	if req.Temperature != 0 {
+		t := req.Temperature
+		out.Temperature = &t
+	}
+	if len(req.StopSequences) > 0 {
+		out.StopSequences = append([]string{}, req.StopSequences...)
+	}
+	// System: Plexum stores System as []Block; Anthropic accepts string
+	// or []ContentBlock. We always use the []block form when we have any
+	// non-trivial blocks so cache_control etc. pass through losslessly.
+	if len(req.System) > 0 {
+		sysBlocks := make([]anthropic.ContentBlock, 0, len(req.System))
+		for _, b := range req.System {
+			sysBlocks = append(sysBlocks, blockToAnthropic(b))
+		}
+		out.System = sysBlocks
+	}
+	// Messages.
+	for _, m := range req.Messages {
+		am := anthropic.Message{Role: roleToAnthropic(m.Role)}
+		for _, b := range m.Content {
+			am.Content = append(am.Content, blockToAnthropic(b))
+		}
+		out.Messages = append(out.Messages, am)
+	}
+	// Tools.
+	for _, t := range req.Tools {
+		out.Tools = append(out.Tools, anthropic.ToolDef{
+			Name: t.Name, Description: t.Description, InputSchema: t.InputSchema,
+		})
+	}
+	if req.ToolChoice != nil {
+		out.ToolChoice = &anthropic.ToolChoice{Type: req.ToolChoice.Type, Name: req.ToolChoice.Name}
+	}
+	if req.Thinking != nil {
+		mode := "disabled"
+		if req.Thinking.Enabled {
+			mode = "enabled"
+		}
+		out.Thinking = &anthropic.ThinkingConfig{
+			Type:         mode,
+			BudgetTokens: req.Thinking.Budget,
+		}
+	}
+	return out, nil
+}
+
+func roleToAnthropic(r canonical.Role) string {
+	switch r {
+	case canonical.RoleUser:
+		return "user"
+	case canonical.RoleAssistant:
+		return "assistant"
+	default:
+		return string(r)
+	}
+}
+
+// blockToAnthropic converts ONE canonical.Block into the loose
+// map-shaped ContentBlock Anthropic expects. Per-type handling:
+//
+//   - TextBlock         → {"type":"text", "text":..., "cache_control"?}
+//   - ToolUseBlock      → {"type":"tool_use", "id":..., "name":..., "input":...}
+//   - ToolResultBlock   → {"type":"tool_result", "tool_use_id":..., "content":[...], "is_error"?}
+//   - ThinkingBlock     → {"type":"thinking", "thinking":..., "signature":...}
+//
+// Unknown block types serialize to their JSON form via canonical's
+// own marshaller (fallback path).
+func blockToAnthropic(b canonical.Block) anthropic.ContentBlock {
+	switch v := b.(type) {
+	case *canonical.TextBlock:
+		out := anthropic.ContentBlock{"type": "text", "text": v.Text}
+		if v.CacheControl != nil {
+			out["cache_control"] = v.CacheControl
+		}
+		return out
+	case *canonical.ToolUseBlock:
+		out := anthropic.ContentBlock{
+			"type": "tool_use", "id": v.ID, "name": v.Name,
+		}
+		if len(v.Input) > 0 {
+			out["input"] = json.RawMessage(v.Input)
+		} else {
+			out["input"] = map[string]any{}
+		}
+		return out
+	case *canonical.ToolResultBlock:
+		inner := make([]anthropic.ContentBlock, 0, len(v.Content))
+		for _, ib := range v.Content {
+			inner = append(inner, blockToAnthropic(ib))
+		}
+		out := anthropic.ContentBlock{
+			"type": "tool_result", "tool_use_id": v.ToolUseID, "content": inner,
+		}
+		if v.IsError {
+			out["is_error"] = true
+		}
+		return out
+	case *canonical.ThinkingBlock:
+		return anthropic.ContentBlock{
+			"type": "thinking", "thinking": v.Thinking, "signature": v.Signature,
+		}
+	default:
+		// Best-effort generic: marshal then unmarshal into a map.
+		raw, err := json.Marshal(b)
+		if err != nil {
+			return anthropic.ContentBlock{"type": "text", "text": fmt.Sprintf("[unsupported block: %T]", b)}
+		}
+		var m map[string]any
+		if err := json.Unmarshal(raw, &m); err != nil {
+			return anthropic.ContentBlock{"type": "text", "text": string(raw)}
+		}
+		return m
+	}
+}
+
+// Translator turns a stream of anthropic.Event into a stream of
+// canonical.TurnEvent. Tracks per-content-block state (current type +
+// id + name) because Anthropic's deltas carry only the block index.
+type Translator struct {
+	// Per-block tracking — index → metadata.
+	blocks   map[int]*blockState
+	finalReason canonical.StopReason
+	finalUsage  canonical.Usage
+}
+
+type blockState struct {
+	Kind string // "text" | "thinking" | "tool_use"
+	ID   string // tool_use only
+	Name string // tool_use only
+}
+
+// NewTranslator constructs a fresh per-turn Translator.
+func NewTranslator() *Translator {
+	return &Translator{blocks: map[int]*blockState{}}
+}
+
+// Translate consumes one anthropic.Event and returns 0..N
+// canonical.TurnEvents. The translator owns no internal channel —
+// caller drives the loop.
+func (t *Translator) Translate(ev anthropic.Event) []canonical.TurnEvent {
+	switch ev.Type {
+	case "message_start":
+		out := []canonical.TurnEvent{{Type: canonical.EventMessageStart}}
+		if ev.Message != nil && ev.Message.Usage != nil {
+			t.finalUsage = toCanonicalUsage(ev.Message.Usage)
+		}
+		return out
+
+	case "ping":
+		return nil // keepalive
+
+	case "content_block_start":
+		if ev.ContentBlock == nil {
+			return nil
+		}
+		st := &blockState{Kind: ev.ContentBlock.Type, ID: ev.ContentBlock.ID, Name: ev.ContentBlock.Name}
+		t.blocks[ev.Index] = st
+		switch st.Kind {
+		case "tool_use":
+			return []canonical.TurnEvent{{
+				Type: canonical.EventToolCallStart, ToolCallID: st.ID, ToolName: st.Name,
+			}}
+		case "text":
+			// Some servers emit content_block_start with non-empty
+			// text seed; surface that.
+			if ev.ContentBlock.Text != "" {
+				return []canonical.TurnEvent{{
+					Type: canonical.EventTextDelta, Text: ev.ContentBlock.Text,
+				}}
+			}
+		case "thinking":
+			if ev.ContentBlock.Thinking != "" {
+				return []canonical.TurnEvent{{
+					Type: canonical.EventThinkingDelta, Thinking: ev.ContentBlock.Thinking,
+				}}
+			}
+		}
+		return nil
+
+	case "content_block_delta":
+		if ev.Delta == nil {
+			return nil
+		}
+		st := t.blocks[ev.Index]
+		switch ev.Delta.Type {
+		case "text_delta":
+			return []canonical.TurnEvent{{Type: canonical.EventTextDelta, Text: ev.Delta.Text}}
+		case "thinking_delta":
+			return []canonical.TurnEvent{{Type: canonical.EventThinkingDelta, Thinking: ev.Delta.Thinking}}
+		case "input_json_delta":
+			if st == nil {
+				return nil
+			}
+			return []canonical.TurnEvent{{
+				Type: canonical.EventToolCallDelta,
+				ToolCallID: st.ID, ToolName: st.Name,
+				PartialJSON: ev.Delta.PartialJSON,
+			}}
+		case "signature_delta":
+			// Signature lands on EventThinkingEnd at block_stop time;
+			// stash on the block state.
+			if st != nil {
+				st.Name = ev.Delta.Signature // reuse Name as scratch
+			}
+			return nil
+		}
+		return nil
+
+	case "content_block_stop":
+		st := t.blocks[ev.Index]
+		if st == nil {
+			return nil
+		}
+		delete(t.blocks, ev.Index)
+		switch st.Kind {
+		case "tool_use":
+			return []canonical.TurnEvent{{
+				Type: canonical.EventToolCallEnd, ToolCallID: st.ID, ToolName: st.Name,
+			}}
+		case "thinking":
+			// st.Name was repurposed to carry the signature in
+			// signature_delta above. Empty when no signature came.
+			return []canonical.TurnEvent{{
+				Type: canonical.EventThinkingEnd, Signature: st.Name,
+			}}
+		}
+		return nil
+
+	case "message_delta":
+		// Carries stop_reason + cumulative usage.
+		if ev.Delta != nil && ev.Delta.StopReason != "" {
+			t.finalReason = canonicalStopReason(ev.Delta.StopReason)
+		}
+		if ev.Usage != nil {
+			// message_delta usage is INCREMENTAL on Anthropic; the v4 docs
+			// describe it as cumulative across the stream. We just take
+			// the last reported values verbatim.
+			t.finalUsage = toCanonicalUsage(ev.Usage)
+		}
+		return nil
+
+	case "message_stop":
+		usage := t.finalUsage
+		return []canonical.TurnEvent{{
+			Type: canonical.EventMessageEnd,
+			StopReason: t.finalReason,
+			Usage: &usage,
+		}}
+
+	case "error":
+		msg := "unknown"
+		etype := "stream_error"
+		if ev.Error != nil {
+			msg = ev.Error.Message
+			etype = ev.Error.Type
+		}
+		return []canonical.TurnEvent{{
+			Type: canonical.EventError,
+			Error: &canonical.ErrorInfo{Code: etype, Message: msg},
+		}}
+	}
+	return nil
+}
+
+func canonicalStopReason(s string) canonical.StopReason {
+	switch s {
+	case "end_turn":
+		return canonical.StopEndTurn
+	case "max_tokens":
+		return canonical.StopMaxTokens
+	case "tool_use":
+		return canonical.StopToolUse
+	case "stop_sequence":
+		return canonical.StopStopSequence
+	default:
+		return canonical.StopReason(s)
+	}
+}
+
+func toCanonicalUsage(u *anthropic.Usage) canonical.Usage {
+	return canonical.Usage{
+		InputTokens:      u.InputTokens,
+		OutputTokens:     u.OutputTokens,
+		CacheReadTokens:  u.CacheReadInputTokens,
+		CacheWriteTokens: u.CacheCreationInputTokens,
+	}
+}