fix: guard widget email-transcript button against repeat clicks (#15095)

## Description

The widget email-transcript button (`ChatFooter.vue`) had no client-side
guard. Its visibility depends only on whether the contact has an email,
and the click handler fired a request on every click with no in-flight
lock, no disabled state, and no post-send handling. A user could
therefore trigger a large number of duplicate transcript emails from a
single conversation just by clicking repeatedly.

This adds a re-entry guard in the handler, disables the button while a
send is in flight, and applies a short cooldown (15s) after a successful
send. Normal use is unaffected: the button sends once, shows the success
toast, then briefly disables and automatically re-enables so a genuine
later re-request still works. On failure the button stays enabled so the
user can retry immediately. The cooldown timer is cleared on unmount.

Using a timed cooldown (rather than a permanent post-send lock) also
avoids the button getting stuck disabled if a resolved conversation is
reopened and later re-resolved.

This is the client-side complement to the server-side rate limit added
in #15085.

Fixes https://linear.app/chatwoot/issue/CW-7640

app/javascript/widget/components/ChatFooter.vue

@@ -11,6 +11,8 @@ import { IFrameHelper } from '../helpers/utils';
 import { CHATWOOT_ON_START_CONVERSATION } from '../constants/sdkEvents';
 import { emitter } from 'shared/helpers/mitt';
 
+const TRANSCRIPT_COOLDOWN_MS = 15000;
+
 export default {
   components: {
     ChatInputWrap,
@@ -24,6 +26,9 @@ export default {
   data() {
     return {
       inReplyTo: null,
+      isSendingTranscript: false,
+      transcriptCooldown: false,
+      transcriptCooldownTimer: null,
     };
   },
   computed: {
@@ -57,6 +62,9 @@ export default {
   mounted() {
     emitter.on(BUS_EVENTS.TOGGLE_REPLY_TO_MESSAGE, this.toggleReplyTo);
   },
+  beforeUnmount() {
+    clearTimeout(this.transcriptCooldownTimer);
+  },
   methods: {
     ...mapActions('conversation', ['sendMessage', 'sendAttachment']),
     ...mapActions('conversationAttributes', ['getAttributes']),
@@ -90,19 +98,35 @@ export default {
     toggleReplyTo(message) {
       this.inReplyTo = message;
     },
+    startTranscriptCooldown() {
+      this.transcriptCooldown = true;
+      clearTimeout(this.transcriptCooldownTimer);
+      this.transcriptCooldownTimer = setTimeout(() => {
+        this.transcriptCooldown = false;
+      }, TRANSCRIPT_COOLDOWN_MS);
+    },
     async sendTranscript() {
-      if (this.hasEmail) {
-        try {
-          await sendEmailTranscript();
-          emitter.emit(BUS_EVENTS.SHOW_ALERT, {
-            message: this.$t('EMAIL_TRANSCRIPT.SEND_EMAIL_SUCCESS'),
-            type: 'success',
-          });
-        } catch (error) {
-          emitter.$emit(BUS_EVENTS.SHOW_ALERT, {
-            message: this.$t('EMAIL_TRANSCRIPT.SEND_EMAIL_ERROR'),
-          });
-        }
+      if (
+        !this.hasEmail ||
+        this.isSendingTranscript ||
+        this.transcriptCooldown
+      ) {
+        return;
+      }
+      this.isSendingTranscript = true;
+      try {
+        await sendEmailTranscript();
+        this.startTranscriptCooldown();
+        emitter.emit(BUS_EVENTS.SHOW_ALERT, {
+          message: this.$t('EMAIL_TRANSCRIPT.SEND_EMAIL_SUCCESS'),
+          type: 'success',
+        });
+      } catch (error) {
+        emitter.emit(BUS_EVENTS.SHOW_ALERT, {
+          message: this.$t('EMAIL_TRANSCRIPT.SEND_EMAIL_ERROR'),
+        });
+      } finally {
+        this.isSendingTranscript = false;
       }
     },
   },
@@ -144,6 +168,7 @@ export default {
       v-if="showEmailTranscriptButton"
       type="clear"
       class="font-normal"
+      :disabled="isSendingTranscript || transcriptCooldown"
       @click="sendTranscript"
     >
       {{ $t('EMAIL_TRANSCRIPT.BUTTON_TEXT') }}