fix: preserve original filename in multipart file upload

BuildFormdata read local files into a bytes.Reader before handing them
to the SDK, so the SDK's part-filename detection (which only reads
*os.File) fell back to "unknown-file" for every local --file upload.
Use AddFileWithName with the file's basename instead.

cmd/api/api_test.go

@@ -4,10 +4,14 @@
 package api
 
 import (
+	"bytes"
 	"context"
 	"encoding/json"
 	"errors"
+	"mime"
+	"mime/multipart"
 	"os"
+	"path/filepath"
 	"sort"
 	"strings"
 	"testing"
@@ -1054,3 +1058,157 @@ func TestApiCmd_JsonFlag_Accepted(t *testing.T) {
 		t.Errorf("expected method GET, got %s", gotOpts.Method)
 	}
 }
+
+// parseMultipartFilenames drives one api --file upload through the mock
+// transport and returns a map of field name -> part filename parsed from the
+// captured multipart body, plus the map of text form fields. It fails the test
+// if the captured request is not multipart/form-data.
+func parseMultipartFilenames(t *testing.T, stub *httpmock.Stub) (map[string]string, map[string]string) {
+	t.Helper()
+	ct := stub.CapturedHeaders.Get("Content-Type")
+	mediaType, params, err := mime.ParseMediaType(ct)
+	if err != nil {
+		t.Fatalf("parse Content-Type %q: %v", ct, err)
+	}
+	if !strings.HasPrefix(mediaType, "multipart/") {
+		t.Fatalf("Content-Type = %q, want multipart/*", mediaType)
+	}
+	filenames := map[string]string{}
+	fields := map[string]string{}
+	mr := multipart.NewReader(bytes.NewReader(stub.CapturedBody), params["boundary"])
+	for {
+		part, err := mr.NextPart()
+		if err != nil {
+			break
+		}
+		if fn := part.FileName(); fn != "" {
+			filenames[part.FormName()] = fn
+		} else {
+			buf := &bytes.Buffer{}
+			_, _ = buf.ReadFrom(part)
+			fields[part.FormName()] = buf.String()
+		}
+	}
+	return filenames, fields
+}
+
+func TestApiCmd_FileUpload_PreservesFilename(t *testing.T) {
+	f, _, _, reg := cmdutil.TestFactory(t, &core.CliConfig{
+		AppID: "test-app", AppSecret: "test-secret", Brand: core.BrandFeishu,
+	})
+
+	dir := t.TempDir()
+	cmdutil.TestChdir(t, dir)
+	if err := os.WriteFile(filepath.Join(dir, "invoice.pdf"), []byte("%PDF-1.4 fake"), 0600); err != nil {
+		t.Fatalf("write test file: %v", err)
+	}
+
+	stub := &httpmock.Stub{
+		URL:  "/open-apis/approval/v4/files/upload",
+		Body: map[string]interface{}{"code": 0, "msg": "success", "data": map[string]interface{}{"code": "file_xxx"}},
+	}
+	reg.Register(stub)
+
+	cmd := NewCmdApi(f, nil)
+	cmd.SetArgs([]string{"POST", "/open-apis/approval/v4/files/upload", "--as", "bot", "--file", "invoice.pdf"})
+	if err := cmd.Execute(); err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	filenames, _ := parseMultipartFilenames(t, stub)
+	if got := filenames["file"]; got != "invoice.pdf" {
+		t.Fatalf("part filename for field %q = %q, want %q", "file", got, "invoice.pdf")
+	}
+}
+
+func TestApiCmd_FileUpload_FieldPrefixKeepsBasename(t *testing.T) {
+	f, _, _, reg := cmdutil.TestFactory(t, &core.CliConfig{
+		AppID: "test-app", AppSecret: "test-secret", Brand: core.BrandFeishu,
+	})
+
+	dir := t.TempDir()
+	cmdutil.TestChdir(t, dir)
+	if err := os.MkdirAll(filepath.Join(dir, "sub"), 0700); err != nil {
+		t.Fatalf("mkdir: %v", err)
+	}
+	if err := os.WriteFile(filepath.Join(dir, "sub", "invoice.pdf"), []byte("%PDF-1.4 fake"), 0600); err != nil {
+		t.Fatalf("write test file: %v", err)
+	}
+
+	stub := &httpmock.Stub{
+		URL:  "/open-apis/approval/v4/files/upload",
+		Body: map[string]interface{}{"code": 0, "msg": "success", "data": map[string]interface{}{"code": "file_xxx"}},
+	}
+	reg.Register(stub)
+
+	cmd := NewCmdApi(f, nil)
+	cmd.SetArgs([]string{"POST", "/open-apis/approval/v4/files/upload", "--as", "bot", "--file", "upload=sub/invoice.pdf"})
+	if err := cmd.Execute(); err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	filenames, _ := parseMultipartFilenames(t, stub)
+	if _, ok := filenames["upload"]; !ok {
+		t.Fatalf("expected field name %q from field=path form, got fields %v", "upload", filenames)
+	}
+	if got := filenames["upload"]; got != "invoice.pdf" {
+		t.Fatalf("part filename for field %q = %q, want %q (basename only)", "upload", got, "invoice.pdf")
+	}
+}
+
+func TestApiCmd_FileUpload_WithDataFields(t *testing.T) {
+	f, _, _, reg := cmdutil.TestFactory(t, &core.CliConfig{
+		AppID: "test-app", AppSecret: "test-secret", Brand: core.BrandFeishu,
+	})
+
+	dir := t.TempDir()
+	cmdutil.TestChdir(t, dir)
+	if err := os.WriteFile(filepath.Join(dir, "invoice.pdf"), []byte("%PDF-1.4 fake"), 0600); err != nil {
+		t.Fatalf("write test file: %v", err)
+	}
+
+	stub := &httpmock.Stub{
+		URL:  "/open-apis/approval/v4/files/upload",
+		Body: map[string]interface{}{"code": 0, "msg": "success", "data": map[string]interface{}{"code": "file_xxx"}},
+	}
+	reg.Register(stub)
+
+	cmd := NewCmdApi(f, nil)
+	cmd.SetArgs([]string{"POST", "/open-apis/approval/v4/files/upload", "--as", "bot",
+		"--file", "invoice.pdf", "--data", `{"type":"attachment"}`})
+	if err := cmd.Execute(); err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	filenames, fields := parseMultipartFilenames(t, stub)
+	if got := filenames["file"]; got != "invoice.pdf" {
+		t.Fatalf("part filename = %q, want %q", got, "invoice.pdf")
+	}
+	if got := fields["type"]; got != "attachment" {
+		t.Fatalf("text field type = %q, want %q", got, "attachment")
+	}
+}
+
+func TestApiCmd_FileUpload_StdinFallsBackToUnknown(t *testing.T) {
+	f, _, _, reg := cmdutil.TestFactory(t, &core.CliConfig{
+		AppID: "test-app", AppSecret: "test-secret", Brand: core.BrandFeishu,
+	})
+	f.IOStreams.In = bytes.NewReader([]byte("stdin-bytes"))
+
+	stub := &httpmock.Stub{
+		URL:  "/open-apis/approval/v4/files/upload",
+		Body: map[string]interface{}{"code": 0, "msg": "success", "data": map[string]interface{}{"code": "file_xxx"}},
+	}
+	reg.Register(stub)
+
+	cmd := NewCmdApi(f, nil)
+	cmd.SetArgs([]string{"POST", "/open-apis/approval/v4/files/upload", "--as", "bot", "--file", "-"})
+	if err := cmd.Execute(); err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	filenames, _ := parseMultipartFilenames(t, stub)
+	if got := filenames["file"]; got != "unknown-file" {
+		t.Fatalf("stdin part filename = %q, want %q (no stable local name, fallback)", got, "unknown-file")
+	}
+}

cmd/service/service_test.go

@@ -4,10 +4,14 @@
 package service
 
 import (
+	"bytes"
 	"context"
 	"encoding/json"
 	"errors"
+	"mime"
+	"mime/multipart"
 	"os"
+	"path/filepath"
 	"strings"
 	"testing"
 
@@ -1132,6 +1136,63 @@ func TestDetectFileFields(t *testing.T) {
 	}
 }
 
+// parseMultipartFilenames drives one service-method --file upload through the
+// mock transport and returns a map of field name -> part filename parsed from
+// the captured multipart body. Mirrors cmd/api's helper of the same name
+// (inlined here rather than shared, since the two live in different packages)
+// to give BuildFormdata's shared local-file fix a second real entry-point
+// covering it.
+func parseMultipartFilenames(t *testing.T, stub *httpmock.Stub) map[string]string {
+	t.Helper()
+	ct := stub.CapturedHeaders.Get("Content-Type")
+	mediaType, params, err := mime.ParseMediaType(ct)
+	if err != nil {
+		t.Fatalf("parse Content-Type %q: %v", ct, err)
+	}
+	if !strings.HasPrefix(mediaType, "multipart/") {
+		t.Fatalf("Content-Type = %q, want multipart/*", mediaType)
+	}
+	filenames := map[string]string{}
+	mr := multipart.NewReader(bytes.NewReader(stub.CapturedBody), params["boundary"])
+	for {
+		part, err := mr.NextPart()
+		if err != nil {
+			break
+		}
+		if fn := part.FileName(); fn != "" {
+			filenames[part.FormName()] = fn
+		}
+	}
+	return filenames
+}
+
+func TestServiceMethod_FileUpload_PreservesFilename(t *testing.T) {
+	f, _, _, reg := cmdutil.TestFactory(t, testConfig)
+
+	dir := t.TempDir()
+	cmdutil.TestChdir(t, dir)
+	if err := os.WriteFile(filepath.Join(dir, "photo.jpg"), []byte("fake-image"), 0600); err != nil {
+		t.Fatalf("write test file: %v", err)
+	}
+
+	stub := &httpmock.Stub{
+		URL:  "/open-apis/im/v1/images",
+		Body: map[string]interface{}{"code": 0, "msg": "ok", "data": map[string]interface{}{"image_key": "img_xxx"}},
+	}
+	reg.Register(stub)
+
+	cmd := NewCmdServiceMethod(f, imSpec(), imImageMethod(), "create", "images", nil)
+	cmd.SetArgs([]string{"--file", "photo.jpg", "--data", `{"image_type":"message"}`, "--as", "bot"})
+	if err := cmd.Execute(); err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	filenames := parseMultipartFilenames(t, stub)
+	if got := filenames["image"]; got != "photo.jpg" {
+		t.Fatalf("part filename for field %q = %q, want %q", "image", got, "photo.jpg")
+	}
+}
+
 func TestServiceMethod_JsonFlag_Accepted(t *testing.T) {
 	f, _, _, _ := cmdutil.TestFactory(t, testConfig)
 

internal/cmdutil/fileupload.go

@@ -7,6 +7,7 @@ import (
 	"bytes"
 	"fmt"
 	"io"
+	"path/filepath"
 	"strconv"
 	"strings"
 
@@ -128,7 +129,7 @@ func BuildFormdata(fileIO fileio.FileIO, fieldName, filePath string, isStdin boo
 				WithParam("--file").
 				WithCause(err)
 		}
-		fd.AddFile(fieldName, bytes.NewReader(data))
+		fd.AddFileWithName(fieldName, filepath.Base(filePath), bytes.NewReader(data))
 	}
 
 	// Add top-level JSON keys as text form fields.