fix: accept an attachment scalar as either a string or a number

internal/api/attachment_date_regression_test.go

@@ -5,17 +5,52 @@ import (
 	"testing"
 )
 
-// TestAttachmentDateUnmarshalsStringFromAPI is a regression test: ClickUp's API
-// returns an attachment "date" as a JSON string (e.g. "1749381600000"), not a
-// number. When Date was typed int64, unmarshalling any task/attachment response
-// failed with "cannot unmarshal string into Go struct field Attachment.date".
-func TestAttachmentDateUnmarshalsStringFromAPI(t *testing.T) {
-	payload := []byte(`{"id":"abc123","version":"0","date":"1749381600000","title":"file.md","extension":"md"}`)
-	var a Attachment
-	if err := json.Unmarshal(payload, &a); err != nil {
-		t.Fatalf("failed to unmarshal attachment with string date: %v", err)
+// ClickUp sends an attachment's scalar fields as either a JSON string or a JSON
+// number, and not consistently per field or per endpoint: `date` arrived as
+// "1749381600000" (#6) and `version` as 0 (2026-08-18). Either one typed as a
+// plain Go scalar breaks unmarshalling of EVERY task response that carries an
+// attachment, which takes out `task get` and `task update` for that task. Both
+// fields are FlexString; this pins both shapes.
+func TestAttachmentScalarsAcceptStringOrNumber(t *testing.T) {
+	for _, tc := range []struct {
+		name        string
+		payload     string
+		wantVersion FlexString
+		wantDate    FlexString
+	}{
+		{
+			name:        "strings",
+			payload:     `{"id":"abc123","version":"0","date":"1749381600000","title":"file.md"}`,
+			wantVersion: "0",
+			wantDate:    "1749381600000",
+		},
+		{
+			name:        "numbers",
+			payload:     `{"id":"abc123","version":0,"date":1749381600000,"title":"file.md"}`,
+			wantVersion: "0",
+			wantDate:    "1749381600000",
+		},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			var a Attachment
+			if err := json.Unmarshal([]byte(tc.payload), &a); err != nil {
+				t.Fatalf("failed to unmarshal attachment: %v", err)
+			}
+			if a.Version != tc.wantVersion {
+				t.Fatalf("version: got %q, want %q", a.Version, tc.wantVersion)
+			}
+			if a.Date != tc.wantDate {
+				t.Fatalf("date: got %q, want %q", a.Date, tc.wantDate)
+			}
+		})
 	}
-	if a.Date != "1749381600000" {
-		t.Fatalf("unexpected date: %q", a.Date)
+}
+
+// A field that is neither shape must fail loudly rather than land as an empty
+// string that reads like a missing value downstream.
+func TestAttachmentScalarRejectsNonScalar(t *testing.T) {
+	var a Attachment
+	if err := json.Unmarshal([]byte(`{"id":"abc","version":{"n":1}}`), &a); err == nil {
+		t.Fatal("expected an error for an object in a FlexString field")
 	}
 }

internal/api/attachments.go

@@ -12,15 +12,38 @@ import (
 	"path/filepath"
 )
 
+// FlexString is a string that also accepts a JSON number. ClickUp is not
+// consistent about which scalar it uses for a field: an attachment's `date`
+// arrives as "1749381600000" while its `version` arrives as 0, and the same
+// field can differ between the attachment endpoint and the copy embedded in a
+// task response. Typing such a field as either Go scalar makes every response
+// carrying an attachment fail to unmarshal, which took out `task get` and
+// `task update` twice (#6, and again on 2026-08-18 with `version`).
+type FlexString string
+
+func (f *FlexString) UnmarshalJSON(b []byte) error {
+	var s string
+	if err := json.Unmarshal(b, &s); err == nil {
+		*f = FlexString(s)
+		return nil
+	}
+	var n json.Number
+	if err := json.Unmarshal(b, &n); err != nil {
+		return fmt.Errorf("value is neither a string nor a number: %s", string(b))
+	}
+	*f = FlexString(n.String())
+	return nil
+}
+
 type Attachment struct {
-	ID             string `json:"id"`
-	Version        string `json:"version"`
-	Date           string `json:"date"`
-	Title          string `json:"title"`
-	Extension      string `json:"extension"`
-	ThumbnailSmall string `json:"thumbnail_small"`
-	ThumbnailLarge string `json:"thumbnail_large"`
-	URL            string `json:"url"`
+	ID             string     `json:"id"`
+	Version        FlexString `json:"version"`
+	Date           FlexString `json:"date"`
+	Title          string     `json:"title"`
+	Extension      string     `json:"extension"`
+	ThumbnailSmall string     `json:"thumbnail_small"`
+	ThumbnailLarge string     `json:"thumbnail_large"`
+	URL            string     `json:"url"`
 }
 
 func (c *Client) CreateTaskAttachment(ctx context.Context, taskID, filePath string, opts ...*TaskScopedOptions) (*Attachment, error) {