fix: keep a named agent on its thread after an empty question and flag a missing Slack signing secret

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

backend/windmill-api/openapi.yaml

@@ -13468,12 +13468,16 @@ paths:
                   slack_team_name:
                     type: string
                     description: the connected Slack workspace; absent when Slack is not connected
+                  signing_secret_set:
+                    type: boolean
+                    description: agents answer in Slack only when the instance sets SLACK_SIGNING_SECRET
                   channels:
                     type: array
                     items:
                       $ref: "#/components/schemas/SlackChannelAgent"
                 required:
                   - channels
+                  - signing_secret_set
 
   /w/{workspace}/flow_conversations/update/{conversation_id}:
     post:

backend/windmill-api/src/slack_agents.rs

@@ -82,6 +82,8 @@ async fn list_channel_agents(
 struct AgentSlack {
     /// The connected Slack workspace's name; `None` when Slack is not connected.
     slack_team_name: Option<String>,
+    /// Agents answer only when the instance verifies Slack's request signatures.
+    signing_secret_set: bool,
     channels: Vec<ChannelAgent>,
 }
 
@@ -111,7 +113,11 @@ async fn list_agent_channels(
     .fetch_all(&mut *tx)
     .await?;
     tx.commit().await?;
-    Ok(Json(AgentSlack { slack_team_name, channels }))
+    #[cfg(feature = "oauth2")]
+    let signing_secret_set = crate::SLACK_SIGNING_SECRET.is_some();
+    #[cfg(not(feature = "oauth2"))]
+    let signing_secret_set = false;
+    Ok(Json(AgentSlack { slack_team_name, signing_secret_set, channels }))
 }
 
 #[derive(Deserialize)]
@@ -653,14 +659,14 @@ async fn answer(
         }
     };
 
+    record_thread_agent(db, &msg.team_id, &channel, &thread_root, w_id, &agent_path).await?;
+
     if question.is_empty() {
         return reply
             .send(format!("What would you like to ask `{agent_path}`?"), None)
             .await;
     }
 
-    record_thread_agent(db, &msg.team_id, &channel, &thread_root, w_id, &agent_path).await?;
-
     // Keyed with the workspace's secret: any member could rebuild the plain thread and user ids
     // and load this person's conversation, tool results included, through the run API.
     let workspace_key = get_workspace_key(w_id, db).await?;

frontend/src/lib/components/flows/content/AgentUsePanel.svelte

@@ -19,6 +19,7 @@
 		workspace,
 		isAdmin,
 		slackTeamName,
+		signingSecretSet,
 		channels,
 		onChanged
 	}: {
@@ -27,6 +28,8 @@
 		isAdmin: boolean
 		/** Unset when Slack is not connected to the workspace. */
 		slackTeamName: string | undefined
+		/** Agents answer in Slack only when the instance verifies Slack's request signatures. */
+		signingSecretSet: boolean
 		channels: SlackChannelAgent[]
 		onChanged: () => void
 	} = $props()
@@ -148,6 +151,12 @@
 							<span class="text-2xs text-hint">A workspace admin can connect it.</span>
 						{/if}
 					{:else}
+						{#if !signingSecretSet}
+							<Alert type="warning" title="Agents can't answer in Slack yet" size="xs">
+								The instance needs SLACK_SIGNING_SECRET set to the Slack app's signing secret, so
+								Windmill can tell who sent a message.
+							</Alert>
+						{/if}
 						<div class="flex flex-col gap-1">
 							<span class="text-xs font-semibold text-emphasis">Ask it anywhere</span>
 							<span class="text-xs text-secondary">

frontend/src/routes/(root)/(logged)/agents/get/[...path]/+page.svelte

@@ -214,6 +214,7 @@
 						workspace={ws}
 						isAdmin={!!($userStore?.is_admin || $userStore?.is_super_admin)}
 						slackTeamName={slack.current?.slack_team_name}
+						signingSecretSet={slack.current?.signing_secret_set ?? true}
 						channels={slack.current?.channels ?? []}
 						onChanged={() => slack.refetch()}
 					/>