google_workspace/gmail_addon/CodeAddon.gs

const ADDON_CONFIG = {
  TRIAGE_API_URL: 'https://REPLACE_WITH_CLOUD_RUN_URL/api/triage',
  TRIAGE_API_KEY: 'REPLACE_WITH_TRIAGE_API_KEY'
};

function buildAddonHome(e) {
  const section = CardService.newCardSection()
    .addWidget(CardService.newTextParagraph().setText(
      '<b>Mail Triage Assistant</b><br/>Open any Gmail message to see AI triage, suggested actions, and a reply draft.'
    ));

  const card = CardService.newCardBuilder()
    .setHeader(CardService.newCardHeader().setTitle('Mail Triage Assistant'))
    .addSection(section)
    .build();

  return card;
}

function buildContextCard(e) {
  try {
    const message = getOpenMessage_(e);
    const triage = callTriageApi_({
      subject: message.getSubject() || '',
      sender: message.getFrom() || '',
      body: message.getPlainBody() || ''
    });

    const actions = (triage.suggested_actions || []).join(', ') || 'None';
    const section = CardService.newCardSection()
      .addWidget(CardService.newKeyValue().setTopLabel('Category').setContent(String(triage.category || 'unknown')))
      .addWidget(CardService.newKeyValue().setTopLabel('Urgency').setContent(String(triage.urgency || 'unknown')))
      .addWidget(CardService.newKeyValue().setTopLabel('Suggested Actions').setContent(actions))
      .addWidget(CardService.newTextParagraph().setText('<b>Reasoning:</b><br/>' + sanitize_(triage.reasoning || 'N/A')))
      .addWidget(
        CardService.newTextInput()
          .setFieldName('draftReply')
          .setTitle('Reply Draft')
          .setMultiline(true)
          .setValue(String(triage.suggested_reply || ''))
      );

    const draftAction = CardService.newAction()
      .setFunctionName('createDraftReplyFromCard')
      .setParameters({ messageId: String(e.gmail.messageId || '') });

    section.addWidget(
      CardService.newTextButton()
        .setText('Create Gmail Draft Reply')
        .setOnClickAction(draftAction)
    );

    const card = CardService.newCardBuilder()
      .setHeader(CardService.newCardHeader().setTitle('AI Triage Results'))
      .addSection(section)
      .build();

    return [card];
  } catch (err) {
    const errorCard = CardService.newCardBuilder()
      .setHeader(CardService.newCardHeader().setTitle('Mail Triage Assistant'))
      .addSection(
        CardService.newCardSection()
          .addWidget(CardService.newTextParagraph().setText('Could not process this email.<br/>' + sanitize_(String(err))))
      )
      .build();

    return [errorCard];
  }
}

function createDraftReplyFromCard(e) {
  const message = getOpenMessage_(e);
  const replyText = getFormText_(e, 'draftReply');

  if (!replyText || !replyText.trim()) {
    return CardService.newActionResponseBuilder()
      .setNotification(CardService.newNotification().setText('Reply draft is empty.'))
      .build();
  }

  message.createDraftReply(replyText);

  return CardService.newActionResponseBuilder()
    .setNotification(CardService.newNotification().setText('Draft reply created in Gmail.'))
    .build();
}

function getOpenMessage_(e) {
  const accessToken = e && e.gmail && e.gmail.accessToken;
  const messageId = e && e.gmail && e.gmail.messageId;

  if (!accessToken || !messageId) {
    throw new Error('Missing Gmail event context (access token or message id).');
  }

  GmailApp.setCurrentMessageAccessToken(accessToken);
  return GmailApp.getMessageById(messageId);
}

function getFormText_(e, fieldName) {
  try {
    return e.commonEventObject.formInputs[fieldName].stringInputs.value[0] || '';
  } catch (err) {
    return '';
  }
}

function sanitize_(s) {
  return String(s)
    .replace(/&/g, '&amp;')
    .replace(/</g, '&lt;')
    .replace(/>/g, '&gt;');
}

function callTriageApi_(payload) {
  const response = UrlFetchApp.fetch(ADDON_CONFIG.TRIAGE_API_URL, {
    method: 'post',
    contentType: 'application/json',
    headers: {
      'x-api-key': ADDON_CONFIG.TRIAGE_API_KEY
    },
    payload: JSON.stringify(payload),
    muteHttpExceptions: true
  });

  const code = response.getResponseCode();
  if (code < 200 || code >= 300) {
    throw new Error('Triage API HTTP ' + code + ': ' + response.getContentText());
  }

  return JSON.parse(response.getContentText());
}