fix(slack): apply open policy consistently to slash commands

Address reviewer feedback: slash commands now use the same
hasExplicitConfig check as regular messages, so unlisted
channels are allowed under groupPolicy: "open" for both
message handling and slash commands.

src/slack/monitor/slash.ts

@@ -262,8 +262,7 @@ export function registerSlackMonitorSlashCommands(params: {
               groupPolicy: ctx.groupPolicy,
               channelAllowlistConfigured,
               channelAllowed,
-            }) ||
+            })
-            !channelAllowed
           ) {
             await respond({
               text: "This channel is not allowed.",
@@ -271,8 +270,11 @@ export function registerSlackMonitorSlashCommands(params: {
             });
             return;
           }
-        }
+          // When groupPolicy is "open", only block channels that are EXPLICITLY denied
-        if (ctx.useAccessGroups && channelConfig?.allowed === false) {
+          // (i.e., have a matching config entry with allow:false). Channels not in the
+          // config (matchSource undefined) should be allowed under open policy.
+          const hasExplicitConfig = Boolean(channelConfig?.matchSource);
+          if (!channelAllowed && (ctx.groupPolicy !== "open" || hasExplicitConfig)) {
             await respond({
               text: "This channel is not allowed.",
               response_type: "ephemeral",
@@ -280,6 +282,7 @@ export function registerSlackMonitorSlashCommands(params: {
             return;
           }
         }
+      }
 
       const sender = await ctx.resolveUserName(command.user_id);
       const senderName = sender?.name ?? command.user_name ?? command.user_id;