fix(mail): remove tip key from default draft-saved envelope

Remove tip field from buildDraftSavedOutput's returned map and flip the
test assertions in TestBuildDraftSavedOutputIncludesReferenceOnlyWhenPresent
to require tip absence. The compose-family default envelope (+send /
+reply / +reply-all / +forward) now stays within the 3-key contract
(compose_hint / draft_id / reference) defined in tech-design v1 §4.1.5.

hintSendDraft already writes the equivalent guidance to stderr, so no
UX regression — the message reaches the user via the dedicated stderr
hint channel instead of the structured stdout envelope.

sprint: S3

Author: bubbmon233

shortcuts/mail/helpers.go

@@ -2193,9 +2193,9 @@ func buildDraftSendOutput(resData map[string]interface{}, mailboxID string) map[
 // buildDraftSavedOutput formats a successful drafts.create / drafts.update
 // response into the public output map (draft_id + optional preview URL).
 func buildDraftSavedOutput(draftResult draftpkg.DraftResult, mailboxID string) map[string]interface{} {
+	_ = mailboxID // retained for caller-signature compatibility; default envelope no longer emits a tip key
 	out := map[string]interface{}{
 		"draft_id": draftResult.DraftID,
-		"tip":      fmt.Sprintf(`draft saved. To send: lark-cli mail user_mailbox.drafts send --params '{"user_mailbox_id":"%s","draft_id":"%s"}'`, mailboxID, draftResult.DraftID),
 	}
 	if draftResult.Reference != "" {
 		out["reference"] = draftResult.Reference

shortcuts/mail/mail_send_confirm_output_test.go

@@ -87,8 +87,8 @@ func TestBuildDraftSavedOutputIncludesReferenceOnlyWhenPresent(t *testing.T) {
 	if withReference["reference"] != "https://www.feishu.cn/mail?draftId=draft_001" {
 		t.Fatalf("reference = %v", withReference["reference"])
 	}
-	if withReference["tip"] == "" {
-		t.Fatalf("tip should be populated")
+	if _, ok := withReference["tip"]; ok {
+		t.Fatalf("tip should be omitted from default envelope, got %#v", withReference["tip"])
 	}
 
 	withoutReference := buildDraftSavedOutput(draftpkg.DraftResult{
@@ -100,8 +100,8 @@ func TestBuildDraftSavedOutputIncludesReferenceOnlyWhenPresent(t *testing.T) {
 	if _, ok := withoutReference["reference"]; ok {
 		t.Fatalf("reference should be omitted, got %#v", withoutReference["reference"])
 	}
-	if withoutReference["tip"] == "" {
-		t.Fatalf("tip should be populated")
+	if _, ok := withoutReference["tip"]; ok {
+		t.Fatalf("tip should be omitted from default envelope, got %#v", withoutReference["tip"])
 	}
 }