improvement(mothership): add workflow lint for custom tool/skills/mcp tool additions to agent block (#5199)

* improvement(workflow-linter): added custom tool validation to workflow linter

* fix(comments): address pr comments

* improvement(validation): ensure type is known

Author: Sg312

apps/sim/lib/copilot/tools/server/workflow/edit-workflow/index.ts

@@ -44,6 +44,7 @@ import {
 } from './lint'
 import { type EditWorkflowParams, isDeferredSkippedItem, type ValidationError } from './types'
 import {
+  collectUnresolvedAgentToolReferences,
   collectUnresolvedReferences,
   preValidateCredentialInputs,
   UNRESOLVABLE_AT_LINT_NOTE,
@@ -190,6 +191,31 @@ export const editWorkflowServerTool: BaseServerTool<EditWorkflowParams, unknown>
           error: toError(error).message,
         })
       }
+
+      // Resolve agent-block tool/skill references (custom tools, MCP servers,
+      // skills). A well-shaped entry whose id does not resolve is dropped at
+      // runtime, so the agent silently loses the tool/skill - surface it through
+      // the same lint + input-validation channels as credential/resource refs.
+      try {
+        const toolReferences = await collectUnresolvedAgentToolReferences(modifiedWorkflowState, {
+          userId: context.userId,
+          workspaceId,
+        })
+        unresolvedReferences.push(...toolReferences)
+        validationErrors.push(
+          ...toolReferences.map((ref) => ({
+            blockId: ref.blockId,
+            blockType: ref.blockType ?? 'agent',
+            field: ref.field,
+            value: ref.value,
+            error: ref.reason,
+          }))
+        )
+      } catch (error) {
+        logger.warn('Agent tool/skill reference validation failed', {
+          error: toError(error).message,
+        })
+      }
     }
 
     // Validate the workflow state

apps/sim/lib/copilot/tools/server/workflow/edit-workflow/lint.ts

@@ -65,11 +65,11 @@ export interface WorkflowLintFieldIssue extends WorkflowLintBlockRef {
   inactiveModeValues: InactiveModeValue[]
 }
 
-/** Tier-2 (async, DB) credential/resource reference that does not resolve to an accessible entity. */
+/** Tier-2 (async, DB) reference that does not resolve to an accessible entity. */
 export interface WorkflowLintUnresolvedReference extends WorkflowLintBlockRef {
   field: string
   value: string | string[]
-  kind: 'credential' | 'resource'
+  kind: 'credential' | 'resource' | 'custom-tool' | 'mcp-tool' | 'skill'
   reason: string
 }
 
@@ -351,9 +351,23 @@ export function formatWorkflowLintMessage(lint: WorkflowLintIssueView) {
   }
 
   const unresolved = lint.unresolvedReferences ?? []
-  if (unresolved.length > 0) {
+  const credResourceRefs = unresolved.filter(
+    (ref) => ref.kind === 'credential' || ref.kind === 'resource'
+  )
+  if (credResourceRefs.length > 0) {
+    parts.push(
+      `Credential/resource references that do not resolve: ${credResourceRefs
+        .map((ref) => `"${ref.blockName || ref.blockId}".${ref.field} (${ref.reason})`)
+        .join(', ')}`
+    )
+  }
+
+  const toolSkillRefs = unresolved.filter(
+    (ref) => ref.kind === 'custom-tool' || ref.kind === 'mcp-tool' || ref.kind === 'skill'
+  )
+  if (toolSkillRefs.length > 0) {
     parts.push(
-      `Credential/resource references that do not resolve: ${unresolved
+      `Agent tool/skill references that do not resolve (they will not attach at runtime): ${toolSkillRefs
         .map((ref) => `"${ref.blockName || ref.blockId}".${ref.field} (${ref.reason})`)
         .join(', ')}`
     )