fix(mcp): fix caret misalignment and tool schema contract validation (#5566)

* fix(mcp): fix caret misalignment in Add MCP Server modal fields

The Server URL and Header fields render a transparent input under a
formatted overlay div for env-var highlighting. The overlay used
font-medium/font-sans but the real input didn't, so glyph widths
diverged and the native caret drifted from the visible text as you
typed.

* fix(mcp): loosen tool schema contract to accept valid JSON Schema shapes

discoverMcpToolsContract's property schema rejected legal JSON Schema
that real MCP servers can return: array-form `items` (tuple
validation) and non-primitive `enum` values. Any server exercising
either shape failed contract validation client-side and blanked the
entire MCP tools list.

* fix(mcp): only render dropdown UI for primitive-valued enums

The MCP dynamic-args dropdown stringifies enum members for its
labels/values. Now that the tool schema contract accepts
non-primitive enum members (object/array), routing those through the
dropdown would collapse distinct values to "[object Object]" and
submit that string as the tool argument. Gate the dropdown on
primitive-only enums; non-primitive enums fall through to the
existing type-based branching (the JSON long-input editor for
object/array types), which round-trips arbitrary JSON correctly.

* fix(mcp): route non-primitive enums to the JSON editor regardless of type

isPrimitiveEnum() correctly excluded object/array enum members from
the dropdown, but the fallback only reached the long-input JSON
editor when paramSchema.type was 'array'. An object-typed (or
untyped) param with a non-primitive enum fell through to the default
short-input, which stringifies via toString() and drops the
enum-membership guarantee entirely. Any non-primitive enum now routes
straight to long-input, independent of the declared type.

* chore(mcp): fold inline comment into the existing TSDoc block

* fix(mcp): serialize non-string values before displaying in the long-input editor

The long-input JSON editor received value={value || ''} unconditionally,
so an argument already holding a parsed object/array (loaded from the
block's JSON arguments field) rendered as "[object Object]" or a
comma-joined list instead of valid JSON, and saving would overwrite the
real value with that mangled text. Serialize non-string values with
JSON.stringify before display; onChange still stores the raw text the
user edits, unchanged.

* fix(mcp): parse JSON-typed long-input edits back into real values

The long-input editor's onChange always stored the raw typed text, so
a param whose schema requires an object/array/non-primitive-enum value
(e.g. entering {"mode":"strict"}) was persisted as a string, not the
actual JSON value — the MCP tool call could receive the wrong type.
requiresJsonValue() identifies these schemas; onChange now parses the
edited text back into the real value once it's valid JSON, falling
back to the raw string mid-edit so the controlled textarea keeps
reflecting in-progress keystrokes.

apps/sim/app/workspace/[workspaceId]/settings/components/mcp/components/mcp-server-form-modal/mcp-server-form-modal.tsx

@@ -157,7 +157,7 @@ function FormattedInput({
         onChange={onChange}
         onScroll={handleScroll}
         onInput={handleScroll}
-        inputClassName='text-transparent caret-[var(--text-primary)]'
+        inputClassName='font-medium font-sans text-transparent caret-[var(--text-primary)]'
       />
       <div className='pointer-events-none absolute inset-0 flex items-center overflow-hidden px-2 py-1.5 font-medium font-sans text-sm'>
         <div className='whitespace-nowrap' style={{ transform: `translateX(-${scrollLeft}px)` }}>

apps/sim/app/workspace/[workspaceId]/w/[workflowId]/components/panel/components/editor/components/sub-block/components/mcp-dynamic-args/mcp-dynamic-args.tsx

@@ -15,6 +15,33 @@ import { formatParameterLabel } from '@/tools/params'
 
 const logger = createLogger('McpDynamicArgs')
 
+/**
+ * The dropdown UI renders each enum member as a string label/value, so it can only
+ * represent JSON Schema enums whose members are primitives — a non-primitive member
+ * (object/array) would collapse to "[object Object]" and lose its identity. Callers
+ * route a non-primitive enum to the JSON editor (`long-input`) instead.
+ */
+function isPrimitiveEnum(
+  enumValues: unknown
+): enumValues is Array<string | number | boolean | null> {
+  return (
+    Array.isArray(enumValues) &&
+    enumValues.every((value) => value === null || typeof value !== 'object')
+  )
+}
+
+/**
+ * True when the schema's actual value must be a JSON object/array (a plain
+ * object/array type, or a non-primitive enum member) rather than a string.
+ */
+function requiresJsonValue(paramSchema: any): boolean {
+  return (
+    paramSchema.type === 'object' ||
+    paramSchema.type === 'array' ||
+    (Array.isArray(paramSchema.enum) && !isPrimitiveEnum(paramSchema.enum))
+  )
+}
+
 interface McpDynamicArgsProps {
   blockId: string
   subBlockId: string
@@ -116,7 +143,9 @@ export function McpDynamicArgs({
   )
 
   const getInputType = (paramSchema: any) => {
-    if (paramSchema.enum) return 'dropdown'
+    if (Array.isArray(paramSchema.enum)) {
+      return isPrimitiveEnum(paramSchema.enum) ? 'dropdown' : 'long-input'
+    }
     if (paramSchema.type === 'boolean') return 'switch'
     if (paramSchema.type === 'number' || paramSchema.type === 'integer') {
       if (paramSchema.minimum !== undefined && paramSchema.maximum !== undefined) {
@@ -241,6 +270,8 @@ export function McpDynamicArgs({
 
       case 'long-input': {
         const config = createParamConfig(paramName, paramSchema, 'long-input')
+        const displayValue =
+          typeof value === 'string' || value == null ? value || '' : JSON.stringify(value)
         return (
           <LongInput
             key={`${paramName}-long`}
@@ -249,8 +280,18 @@ export function McpDynamicArgs({
             config={config}
             placeholder={config.placeholder}
             rows={4}
-            value={value || ''}
-            onChange={(newValue) => updateParameter(paramName, newValue)}
+            value={displayValue}
+            onChange={(newValue) => {
+              if (!requiresJsonValue(paramSchema)) {
+                updateParameter(paramName, newValue)
+                return
+              }
+              try {
+                updateParameter(paramName, JSON.parse(newValue))
+              } catch {
+                updateParameter(paramName, newValue)
+              }
+            }}
             isPreview={isPreview}
             disabled={disabled}
             workflowSearchValuePath={[paramName]}

apps/sim/lib/api/contracts/mcp.ts

@@ -50,10 +50,12 @@ export const mcpToolSchemaPropertySchema: z.ZodType<McpToolSchemaProperty> = z.l
     .object({
       type: z.union([z.string(), z.array(z.string())]).optional(),
       description: z.string().optional(),
-      items: mcpToolSchemaPropertySchema.optional(),
+      items: z
+        .union([mcpToolSchemaPropertySchema, z.array(mcpToolSchemaPropertySchema)])
+        .optional(),
       properties: z.record(z.string(), mcpToolSchemaPropertySchema).optional(),
       required: z.array(z.string()).optional(),
-      enum: z.array(z.union([z.string(), z.number(), z.boolean(), z.null()])).optional(),
+      enum: z.array(z.unknown()).optional(),
       default: z.unknown().optional(),
     })
     .passthrough()

apps/sim/lib/mcp/types.ts

@@ -68,10 +68,10 @@ export interface McpSecurityPolicy {
 export interface McpToolSchemaProperty {
   type?: string | string[]
   description?: string
-  items?: McpToolSchemaProperty
+  items?: McpToolSchemaProperty | McpToolSchemaProperty[]
   properties?: Record<string, McpToolSchemaProperty>
   required?: string[]
-  enum?: Array<string | number | boolean | null>
+  enum?: unknown[]
   default?: unknown
   [key: string]: unknown
 }