fix: extract event-specific fields for Slack reaction webhooks

- Add fetchSlackReactionMessageText helper to fetch original message text
  via conversations.history API for reaction_added/reaction_removed events
- Handle reaction events separately with correct field extraction:
  - channel: extract from event.item.channel (not event.channel)
  - timestamp: use item.ts (message timestamp) not event_ts (reaction time)
  - reaction: extract emoji name from event.reaction
  - item_user: extract message author from event.item_user
  - event_ts: new field for when the reaction was added/removed
  - text: fetch via API if bot token has channels:history scope
- Gracefully handle missing permissions (missing_scope error)
- Update Slack trigger outputs to document new reaction fields
- Add channels:history and reactions:read scopes to setup instructions

Co-authored-by: Emir Karabeg <emir-karabeg@users.noreply.github.com>

Author: cursoragent

apps/sim/lib/webhooks/utils.server.ts

@@ -530,6 +530,66 @@ export async function validateTwilioSignature(
 const SLACK_MAX_FILE_SIZE = 50 * 1024 * 1024 // 50 MB
 const SLACK_MAX_FILES = 15
 
+/**
+ * Fetches the original message text for a reaction event using conversations.history.
+ * Reaction events don't include message text, so we need to fetch it separately.
+ * Returns empty string if permissions are missing or fetch fails.
+ */
+async function fetchSlackReactionMessageText(
+  channel: string,
+  messageTs: string,
+  botToken: string
+): Promise<{ text: string; user?: string }> {
+  try {
+    const url = new URL('https://slack.com/api/conversations.history')
+    url.searchParams.append('channel', channel)
+    url.searchParams.append('oldest', messageTs)
+    url.searchParams.append('limit', '1')
+    url.searchParams.append('inclusive', 'true')
+
+    const response = await fetch(url.toString(), {
+      method: 'GET',
+      headers: {
+        'Content-Type': 'application/json',
+        Authorization: `Bearer ${botToken}`,
+      },
+    })
+
+    const data = (await response.json()) as {
+      ok: boolean
+      error?: string
+      messages?: Array<{ text?: string; user?: string }>
+    }
+
+    if (!data.ok) {
+      if (data.error === 'missing_scope') {
+        logger.debug('Missing scope for fetching reaction message text - channels:history required')
+      } else if (data.error === 'channel_not_found') {
+        logger.debug('Channel not found when fetching reaction message text', { channel })
+      } else {
+        logger.warn('Failed to fetch reaction message text', { error: data.error, channel })
+      }
+      return { text: '' }
+    }
+
+    const messages = data.messages || []
+    if (messages.length === 0) {
+      return { text: '' }
+    }
+
+    return {
+      text: messages[0].text || '',
+      user: messages[0].user,
+    }
+  } catch (error) {
+    logger.warn('Error fetching reaction message text', {
+      error: error instanceof Error ? error.message : String(error),
+      channel,
+    })
+    return { text: '' }
+  }
+}
+
 /**
  * Resolves the full file object from the Slack API when the event payload
  * only contains a partial file (e.g. missing url_private due to file_access restrictions).
@@ -953,6 +1013,51 @@ export async function formatWebhookInput(
       })
     }
 
+    const eventType = rawEvent?.type || body?.type || 'unknown'
+
+    // Handle reaction events (reaction_added, reaction_removed) which have a different payload structure
+    const isReactionEvent = eventType === 'reaction_added' || eventType === 'reaction_removed'
+
+    if (isReactionEvent) {
+      // Reaction events have item.channel instead of channel, and item.ts for the message timestamp
+      const itemChannel = rawEvent?.item?.channel || ''
+      const itemTs = rawEvent?.item?.ts || ''
+      const reaction = rawEvent?.reaction || ''
+      const itemUser = rawEvent?.item_user || ''
+
+      // Fetch the original message text if bot token is available
+      let messageText = ''
+      let messageAuthor = itemUser
+      if (botToken && itemChannel && itemTs) {
+        const messageData = await fetchSlackReactionMessageText(itemChannel, itemTs, botToken)
+        messageText = messageData.text
+        if (messageData.user) {
+          messageAuthor = messageData.user
+        }
+      }
+
+      return {
+        event: {
+          event_type: eventType,
+          channel: itemChannel,
+          channel_name: '',
+          user: rawEvent?.user || '',
+          user_name: '',
+          text: messageText,
+          reaction,
+          item_user: messageAuthor,
+          timestamp: itemTs,
+          event_ts: rawEvent?.event_ts || '',
+          thread_ts: '',
+          team_id: body?.team_id || rawEvent?.team || '',
+          event_id: body?.event_id || '',
+          hasFiles: false,
+          files: [],
+        },
+      }
+    }
+
+    // Standard message events
     const rawFiles: any[] = rawEvent?.files ?? []
     const hasFiles = rawFiles.length > 0
 
@@ -965,7 +1070,7 @@ export async function formatWebhookInput(
 
     return {
       event: {
-        event_type: rawEvent?.type || body?.type || 'unknown',
+        event_type: eventType,
         channel: rawEvent?.channel || '',
         channel_name: '',
         user: rawEvent?.user || '',

apps/sim/triggers/slack/webhook.ts

@@ -67,7 +67,7 @@ export const slackWebhookTrigger: TriggerConfig = {
         'Go to <a href="https://api.slack.com/apps" target="_blank" rel="noopener noreferrer" class="text-muted-foreground underline transition-colors hover:text-muted-foreground/80">Slack Apps page</a>',
         'If you don\'t have an app:<br><ul class="mt-1 ml-5 list-disc"><li>Create an app from scratch</li><li>Give it a name and select your workspace</li></ul>',
         'Go to "Basic Information", find the "Signing Secret", and paste it in the field above.',
-        'Go to "OAuth & Permissions" and add bot token scopes:<br><ul class="mt-1 ml-5 list-disc"><li><code>app_mentions:read</code> - For viewing messages that tag your bot with an @</li><li><code>chat:write</code> - To send messages to channels your bot is a part of</li><li><code>files:read</code> - To access files and images shared in messages</li></ul>',
+        'Go to "OAuth & Permissions" and add bot token scopes:<br><ul class="mt-1 ml-5 list-disc"><li><code>app_mentions:read</code> - For viewing messages that tag your bot with an @</li><li><code>chat:write</code> - To send messages to channels your bot is a part of</li><li><code>files:read</code> - To access files and images shared in messages</li><li><code>channels:history</code> - To fetch message text for reaction events</li><li><code>reactions:read</code> - To receive reaction events</li></ul>',
         'Go to "Event Subscriptions":<br><ul class="mt-1 ml-5 list-disc"><li>Enable events</li><li>Under "Subscribe to Bot Events", add <code>app_mention</code> to listen to messages that mention your bot</li><li>Paste the Webhook URL above into the "Request URL" field</li></ul>',
         'Go to "Install App" in the left sidebar and install the app into your desired Slack workspace and channel.',
         'Copy the "Bot User OAuth Token" (starts with <code>xoxb-</code>) and paste it in the Bot Token field above to enable file downloads.',
@@ -90,7 +90,8 @@ export const slackWebhookTrigger: TriggerConfig = {
       properties: {
         event_type: {
           type: 'string',
-          description: 'Type of Slack event (e.g., app_mention, message)',
+          description:
+            'Type of Slack event (e.g., app_mention, message, reaction_added, reaction_removed)',
         },
         channel: {
           type: 'string',
@@ -102,19 +103,35 @@ export const slackWebhookTrigger: TriggerConfig = {
         },
         user: {
           type: 'string',
-          description: 'User ID who triggered the event',
+          description:
+            'User ID who triggered the event (for reactions, the user who added/removed the reaction)',
         },
         user_name: {
           type: 'string',
           description: 'Username who triggered the event',
         },
         text: {
           type: 'string',
-          description: 'Message text content',
+          description:
+            'Message text content. For reaction events, fetched via API if bot token has channels:history scope.',
+        },
+        reaction: {
+          type: 'string',
+          description: 'Emoji name for reaction events (e.g., "thumbsup", "heart")',
+        },
+        item_user: {
+          type: 'string',
+          description: 'User ID of the message author (for reaction events)',
         },
         timestamp: {
           type: 'string',
-          description: 'Message timestamp from the triggering event',
+          description:
+            'Message timestamp. For reactions, this is the timestamp of the reacted-to message (item.ts).',
+        },
+        event_ts: {
+          type: 'string',
+          description:
+            'Event timestamp. For reactions, this is when the reaction was added/removed.',
         },
         thread_ts: {
           type: 'string',