docs(comments): 注释中文化 · internal/runtime/model + internal/services/backthink（54 文件，纯替换）

- 只翻注释/文档字符串：`go/scanner` 剥注释后按 token 序列+literal 逐 token 比对，**54/54 文件 SAME**；
  改动文件总行数与 HEAD 漂移 = 0（严格 1:1，无合并/拆行）
- 裁决编号与 design 节号逐字保留（03.4.1/03.4.2/03.4.3/14.4.1/14.4.5/07.4.2-4、design/04 §3.1/§3.2 等）；
  `chat_template_kwargs` / `enable_thinking` / `reasoning_effort` / `thinking:{type}` 字段名与形状说明未动
- 存疑译法（已登记）：`persona` 在叙事语境用「角色」、标识符语境保留 `persona`（仓库既有模块本身混用）；
  `rung`→「级」；`provider` 存在「提供商/提供者」两种落笔（可按需一键统一）
- 复核：build/vet 绿 + 两包测试绿；gofmt 干净；残留英文注释 0 条
- 既有存量（未修，只报告）：`model/anthropic_test.go` 612 行 >500；`applyAnthropicEvent` 115 行 >80

internal/runtime/model/anthropic_stream.go

@@ -8,9 +8,9 @@ import (
 	"strings"
 )
 
-// anthropicStreamEvent is one SSE payload from /v1/messages with stream: true.
-// Anthropic carries the event kind both in the SSE `event:` field and inside the
-// JSON `type` field, so the parser keys off the JSON payload type.
+// anthropicStreamEvent 是 /v1/messages（stream: true）的一个 SSE 负载。
+// Anthropic 既在 SSE 的 `event:` 字段里、也在 JSON 的 `type` 字段里
+// 携带事件种类，所以解析器按 JSON 负载的 type 取值。
 type anthropicStreamEvent struct {
 	Type    string                `json:"type"`
 	Message *anthropicStartBlock  `json:"message,omitempty"`
@@ -21,30 +21,30 @@ type anthropicStreamEvent struct {
 	Error   *anthropicStreamError `json:"error,omitempty"`
 }
 
-// anthropicStartBlock is the payload of a message_start event.
+// anthropicStartBlock 是 message_start 事件的负载。
 type anthropicStartBlock struct {
 	Model string          `json:"model"`
 	Usage *anthropicUsage `json:"usage,omitempty"`
 }
 
-// anthropicDelta is the incremental payload inside a content_block_delta event.
-// The message_delta event reuses the same field name for its terminal
-// stop_reason (end_turn / max_tokens / tool_use), so it is decoded here too.
+// anthropicDelta 是 content_block_delta 事件里的增量负载。
+// Anthropic 把 message_delta 事件的终止 stop_reason 复用了同一字段名
+// （end_turn / max_tokens / tool_use），所以这里也一并解码。
 type anthropicDelta struct {
-	Type        string `json:"type"` // text_delta | input_json_delta | thinking_delta
+	Type        string `json:"type"` // 取值：text_delta | input_json_delta | thinking_delta
 	Text        string `json:"text,omitempty"`
 	PartialJSON string `json:"partial_json,omitempty"`
 	Thinking    string `json:"thinking,omitempty"`
 	StopReason  string `json:"stop_reason,omitempty"`
 }
 
-// anthropicStreamError is the payload of an error event.
+// anthropicStreamError 是 error 事件的负载。
 type anthropicStreamError struct {
 	Type    string `json:"type"`
 	Message string `json:"message"`
 }
 
-// streamBlock tracks the partial state of one content block during streaming.
+// streamBlock 跟踪流式过程中单个内容块的部分状态。
 type streamBlock struct {
 	index       int
 	typ         string
@@ -55,13 +55,13 @@ type streamBlock struct {
 	initialArgs map[string]any
 }
 
-// scanAnthropicSSE incrementally decodes Anthropic's content-block stream. Text
-// deltas are forwarded as text_delta events (segment bracketed by
-// text_start/text_end); tool_use input_json_delta fragments are forwarded as
-// tool_call_delta events (segment bracketed by tool_call_start/tool_call_end)
-// and accumulated per block so they re-assemble into a structured Args map when
-// the block stops. The stream must terminate with a message_stop event,
-// otherwise ErrStream is returned.
+// scanAnthropicSSE 增量解码 Anthropic 的内容块流。文本
+// 增量以 text_delta 事件转发（片段由
+// text_start/text_end 包起来）；tool_use 的 input_json_delta 片段以
+// tool_call_delta 事件转发（片段由 tool_call_start/tool_call_end 包起来），
+// 并按块累积，以便块结束时重新拼装成结构化的 Args map。
+// 流必须以 message_stop 事件终止，
+// 否则返回 ErrStream。
 func scanAnthropicSSE(r io.Reader, onEvent func(StreamEvent)) (Response, error) {
 	scanner := bufio.NewScanner(r)
 	scanner.Buffer(make([]byte, 0, sseBufInit), maxSSELineBytes)
@@ -101,7 +101,7 @@ func scanAnthropicSSE(r io.Reader, onEvent func(StreamEvent)) (Response, error)
 	return agg, nil
 }
 
-// applyAnthropicEvent folds a single stream event into the running aggregation.
+// applyAnthropicEvent 把单个流事件折叠进正在运行的聚合状态。
 func applyAnthropicEvent(
 	agg *Response,
 	blocks map[int]*streamBlock,
@@ -218,8 +218,8 @@ func applyAnthropicEvent(
 	return nil
 }
 
-// finalizeAnthropicStream assembles the aggregated Response from the accumulated
-// blocks: concatenated text plus any tool_use ToolCalls derived per block.
+// finalizeAnthropicStream 由累积的内容块拼装出聚合后的 Response：
+// 拼接的文本，加上按块导出的 tool_use ToolCall。
 func finalizeAnthropicStream(agg *Response, blocks map[int]*streamBlock, order []int, content string) {
 	agg.Content = content
 	agg.Message = Message{Role: RoleAssistant, Content: []Content{{Type: ContentTypeText, Text: content}}}