fix(slack): render settings multiselects as section accessories

CHANGELOG.md

@@ -18,6 +18,9 @@ product overview.
 
 ## Unreleased
 
+- Fix Slack Settings rejecting the MCP, Skills and You pages with `invalid_arguments` when
+  their multi-select pickers contain options.
+
 - Require a human approval card before managed Composio joins, invites or creates Slack channels,
   including in Auto/Admin mode and through batched actions, both identities and host runtimes.
   Refuse opaque connector code/API executors that could bypass membership approval; use

FEATURES.md

@@ -1,5 +1,8 @@
 # ChannelGate — Features
 
+- Slack Settings renders populated Cloud MCP and skill pickers on the MCP, Skills and You pages
+  without a native Slack `invalid_arguments` error; selection still saves immediately.
+
 ## Slack channel membership approvals
 
 - Managed Composio Slack join, invitation and channel-creation actions require a one-use human

TEST-PLAN.md

@@ -1,5 +1,16 @@
 # ChannelGate — Test Plan
 
+## Slack Settings picker rendering (2026-10-15)
+
+- [x] Regression: the existing all-page/all-role/inline-form Block Kit validation includes a
+  compatibility guard for the deployed modal's live `unsupported element: multiselect`
+  rejection of actions-block placement (current Slack docs also list actions as supported).
+  Cloud MCP, channel skills and personal skills
+  use section accessories, retaining action IDs, block IDs, options and initial selections.
+- [ ] Native retest on the deployed fix: open MCP, Skills and You with populated catalogs;
+  verify each page renders, selection saves and the same modal repaints. Resume the existing
+  Settings navigation/template live cases. Automated rendering checks alone do not close them.
+
 ## Slack channel membership approvals (2026-10-15)
 
 - [x] Automated: `test/composio-approval.test.js`, `test/mcp-socket-server.test.js`,

src/slack/channel-settings.js

@@ -818,10 +818,10 @@ function cloudRows(snapshot) {
       continue;
     }
     const initial = options.filter((entry) => (data.selected || []).includes(entry.value));
-    blocks.push({ type: "actions", block_id: `cg_cloud_${engine}`, elements: [{
+    blocks.push({ type: "section", block_id: `cg_cloud_${engine}`, text: mrkdwn("Select servers"), accessory: {
       type: "multi_static_select", action_id: `${CHANNEL_SETTINGS_CLOUD_SELECT_PREFIX}${engine}`, placeholder: plain("Add a server…"), options,
       ...(initial.length ? { initial_options: initial } : {}),
-    }] });
+    } });
     if (data.inherited?.length) blocks.push(context(`Always on from the organization: ${data.inherited.map(inlineCode).join(" ")}`));
   }
   return blocks;
@@ -902,10 +902,10 @@ function skillPicker(actionId, data = {}, placeholder) {
   const options = (data.options || []).slice(0, 100).map((entry) => option(entry.label || entry.key, entry.key, entry.description || ""));
   const initial = options.filter((entry) => (data.selected || []).includes(entry.value));
   if (!options.length) return [context("_No skills available in the catalog._")];
-  return [{ type: "actions", block_id: `${actionId}_row`, elements: [{
+  return [{ type: "section", block_id: `${actionId}_row`, text: mrkdwn("Select skills"), accessory: {
     type: "multi_static_select", action_id: actionId, placeholder: plain(placeholder), options,
     ...(initial.length ? { initial_options: initial } : {}),
-  }] }, ...((data.options || []).length > 100 ? [context(`Showing 100 of ${data.options.length} skills; the admin UI lists them all.`)] : [])];
+  } }, ...((data.options || []).length > 100 ? [context(`Showing 100 of ${data.options.length} skills; the admin UI lists them all.`)] : [])];
 }
 
 function skillsPage(snapshot, state) {

test/slack-settings-redesign.test.js

@@ -262,6 +262,10 @@ function blockKitProblems(view) {
     if (block.type === "context" && block.elements.length > 10) problems.push(`${where} more than 10 context elements`);
     const elements = [...(block.accessory ? [block.accessory] : []), ...(block.type === "actions" ? block.elements : []), ...(block.type === "input" ? [block.element] : [])];
     if (block.type === "actions" && block.elements.length > 25) problems.push(`${where} more than 25 elements`);
+    // The deployed Slack modal rejected this placement with `unsupported element: multiselect`,
+    // despite current docs also listing actions blocks. Guard that observed compatibility case;
+    // section accessories support the same immediate block_actions callbacks.
+    if (block.type === "actions" && block.elements.some((element) => element.type.startsWith("multi_"))) problems.push(`${where} unsupported multiselect placement`);
     const actionIds = new Set();
     for (const element of elements) {
       if (element.action_id) {
@@ -276,7 +280,7 @@ function blockKitProblems(view) {
   return problems;
 }
 
-test("every page, in every role and with every inline form open, is valid Block Kit", () => {
+test("every page, in every role and with every inline form open, passes Block Kit and deployed modal compatibility checks", () => {
   const masked = (last4) => ({ configured: true, last4 });
   const long = "X".repeat(64);
   const snapshot = {