docs(comments): 注释中文化 · internal/runtime/multimodal（21 文件，纯替换）

- 只翻注释/文档字符串，代码零变化：go/scanner 词法流比对 21 文件 token+字面量全等，增删行数 1:1（467/467）
- 刻意保留非散文英文：JSON Schema description、工具 Description() 返回值、adapter prompt、API 路径与命令示例、环境变量名
- 逐行确认代码前缀未变，未触碰其他模块

internal/runtime/multimodal/vision/image.go

@@ -10,23 +10,23 @@ import (
 	"strings"
 )
 
-// Size caps for reading image bytes and response bodies, so a hostile or
-// malformed source cannot exhaust memory. The 50MB cap matches the file-upload
-// limit in DevDocs/02-development-constraints.md §11.
+// 读取图像字节与响应体的体积上限，使恶意或
+// 畸形来源无法耗尽内存。50MB 上限与
+// DevDocs/02-development-constraints.md §11 的文件上传限制一致。
 const (
 	maxImageBytes  = 50 << 20
 	maxFetchedBody = 50 << 20
 )
 
-// DataURI builds a base64 data: image URI from mime and raw bytes.
+// DataURI 由 mime 与原始字节构造一个 base64 data: 图像 URI。
 func DataURI(mime string, data []byte) string {
 	return "data:" + mime + ";base64," + base64.StdEncoding.EncodeToString(data)
 }
 
-// Resolve loads the bytes for an ImageRef. Paths and base64 payloads are read
-// locally; URLs are fetched with an http.Client (the provided client, or a
-// default one when nil). For base64 input the Data field is returned verbatim as
-// the payload and the MIME type is guessed from a data: prefix.
+// Resolve 加载一个 ImageRef 对应的字节。路径与 base64 载荷在
+// 本地读取；URL 用 http.Client 抓取（传入的 client，为 nil 时
+// 用默认 client）。对 base64 输入，Data 字段原样作为
+// 载荷返回，MIME 类型从 data: 前缀推断。
 func Resolve(ctx context.Context, ref ImageRef, client *http.Client) (mime string, data []byte, err error) {
 	switch ref.Source {
 	case SourcePath:
@@ -40,7 +40,7 @@ func Resolve(ctx context.Context, ref ImageRef, client *http.Client) (mime strin
 	}
 }
 
-// readFile reads an image file and guesses its MIME type from the extension.
+// readFile 读取一个图像文件，并从扩展名推断其 MIME 类型。
 func readFile(path string) (string, []byte, error) {
 	f, err := os.Open(path)
 	if err != nil {
@@ -54,7 +54,7 @@ func readFile(path string) (string, []byte, error) {
 	return mimeByExt(path), data, nil
 }
 
-// decodeBase64 returns the decoded bytes of a base64/data: payload and its MIME.
+// decodeBase64 返回 base64/data: 载荷解码后的字节及其 MIME。
 func decodeBase64(src string) (string, []byte, error) {
 	mime, encoded, isDataURI := splitDataURI(src)
 	if isDataURI {
@@ -71,7 +71,7 @@ func decodeBase64(src string) (string, []byte, error) {
 	return "image/png", decoded, nil
 }
 
-// fetchURL downloads an image over http(s); only http/https schemes are allowed.
+// fetchURL 通过 http(s) 下载一张图像；只允许 http/https 协议。
 func fetchURL(ctx context.Context, rawURL string, client *http.Client) (string, []byte, error) {
 	if !strings.HasPrefix(rawURL, "http://") && !strings.HasPrefix(rawURL, "https://") {
 		return "", nil, fmt.Errorf("vision: %w: %q", ErrUnsupportedSource, rawURL)
@@ -98,8 +98,8 @@ func fetchURL(ctx context.Context, rawURL string, client *http.Client) (string,
 	return mimeByContentType(resp.Header.Get("Content-Type")), data, nil
 }
 
-// splitDataURI parses a "data:<mime>;base64,<payload>" prefix. The second return
-// is false when src is not a data: URI.
+// splitDataURI 解析 "data:<mime>;base64,<payload>" 前缀。src 不是
+// data: URI 时第二个返回值是 false。
 func splitDataURI(src string) (mime, payload string, ok bool) {
 	if !strings.HasPrefix(src, "data:") {
 		return "", "", false
@@ -124,7 +124,7 @@ func splitDataURI(src string) (mime, payload string, ok bool) {
 	return mime, payload, true
 }
 
-// mimeByExt guesses a MIME type from a file path extension.
+// mimeByExt 从文件路径扩展名推断 MIME 类型。
 func mimeByExt(path string) string {
 	switch strings.ToLower(pathExtension(path)) {
 	case ".png":
@@ -140,8 +140,8 @@ func mimeByExt(path string) string {
 	}
 }
 
-// mimeByContentType returns a MIME type from an HTTP Content-Type header,
-// defaulting to image/png when absent or non-image.
+// mimeByContentType 从 HTTP Content-Type 头返回 MIME 类型，
+// 缺失或非图像时默认为 image/png。
 func mimeByContentType(ct string) string {
 	if ct == "" || !strings.HasPrefix(ct, "image/") {
 		return "image/png"
@@ -149,7 +149,7 @@ func mimeByContentType(ct string) string {
 	return strings.TrimSpace(strings.Split(ct, ";")[0])
 }
 
-// pathExtension returns the file extension with its dot, or empty when none.
+// pathExtension 返回带点号的文件扩展名，没有则返回空串。
 func pathExtension(path string) string {
 	base := path
 	if idx := strings.LastIndexByte(path, '/'); idx >= 0 {
@@ -164,15 +164,15 @@ func pathExtension(path string) string {
 	return base[dot:]
 }
 
-// fileExists reports whether path exists on disk and is a regular file.
+// fileExists 报告 path 是否存在于磁盘且为常规文件。
 func fileExists(path string) bool {
 	info, err := os.Stat(path)
 	return err == nil && info.Mode().IsRegular()
 }
 
-// defaultHTTPClient builds the HTTP client described in
-// DevDocs/02-development-constraints.md §2.3. A fresh client is returned per
-// call rather than a package global, which the constraints forbid.
+// defaultHTTPClient 构造 DevDocs/02-development-constraints.md §2.3
+// 所述的 HTTP client。这里每次调用返回一个新 client，
+// 而不是包级全局变量——后者为约束所禁止。
 func defaultHTTPClient() *http.Client {
 	return &http.Client{Transport: http.DefaultTransport}
 }