fix(workflow-mcp): preserve block-default input fields when editing param descriptions

updateFieldDescription read only from the subblock store, but the display memo
falls back to the block's persisted inputFormat when the store entry is empty.
For workflows whose fields are hydrated from block defaults, editing a
description would have written [] and wiped every input field. Extract a shared
resolveInputFormatFields helper used by both the memo and the writer, and guard
against ever persisting an empty list.

Author: waleedlatif1

apps/sim/app/workspace/[workspaceId]/w/[workflowId]/components/panel/components/deploy/components/deploy-modal/components/mcp/mcp.tsx

@@ -64,6 +64,22 @@ function haveSameServerSelection(a: string[], b: string[]): boolean {
   return a.every((id) => bSet.has(id))
 }
 
+/**
+ * Resolves the start block's input fields from the subblock store, falling back
+ * to the block's persisted value when the store entry is empty (fields hydrated
+ * from block defaults). Shared by the display memo and the description writer so
+ * both read the exact same source — a writer that skipped the fallback could
+ * persist `[]` and wipe every field.
+ */
+function resolveInputFormatFields(
+  storeValue: unknown,
+  blockFallbackValue: unknown
+): NormalizedField[] {
+  const fromStore = normalizeInputFormatValue(storeValue) as NormalizedField[]
+  if (fromStore.length > 0) return fromStore
+  return normalizeInputFormatValue(blockFallbackValue) as NormalizedField[]
+}
+
 /**
  * Component to query tools for a single server and report back via callback.
  */
@@ -127,14 +143,10 @@ export function McpDeploy({
 
   const inputFormat = useMemo((): NormalizedField[] => {
     if (!starterBlockId) return []
-
-    const storeValue = subBlockValues[starterBlockId]?.inputFormat
-    const normalized = normalizeInputFormatValue(storeValue) as NormalizedField[]
-    if (normalized.length > 0) return normalized
-
-    const startBlock = blocks[starterBlockId]
-    const blockValue = startBlock?.subBlocks?.inputFormat?.value
-    return normalizeInputFormatValue(blockValue) as NormalizedField[]
+    return resolveInputFormatFields(
+      subBlockValues[starterBlockId]?.inputFormat,
+      blocks[starterBlockId]?.subBlocks?.inputFormat?.value
+    )
   }, [starterBlockId, subBlockValues, blocks])
 
   const [toolName, setToolName] = useState(() => sanitizeToolName(workflowName))
@@ -154,9 +166,13 @@ export function McpDeploy({
   const updateFieldDescription = useCallback(
     (fieldName: string, description: string) => {
       if (!starterBlockId) return
-      const currentFields = normalizeInputFormatValue(
-        useSubBlockStore.getState().getValue(starterBlockId, 'inputFormat')
-      ) as NormalizedField[]
+      const currentFields = resolveInputFormatFields(
+        useSubBlockStore.getState().getValue(starterBlockId, 'inputFormat'),
+        useWorkflowStore.getState().blocks[starterBlockId]?.subBlocks?.inputFormat?.value
+      )
+      // Never persist an empty list: the description inputs only render when fields
+      // exist, so an empty resolution means a transient state we must not write back.
+      if (currentFields.length === 0) return
       const nextFields = currentFields.map((field) =>
         field.name === fieldName ? { ...field, description } : field
       )