fix(mcp): keep declared fields in deps whole reads and sample __proto__ fields safely

workflows deps now adds an operation's declared fields wherever a consumer reads a structuredContent value whole, beside the paths it reads by name. Trigger mock payloads define sampled fields with Object.fromEntries, so a declared __proto__ field stays a field instead of replacing the sample's prototype.

Author: waleedlatif1

apps/sim/lib/mothership/agent-cli/engines.test.ts

@@ -340,6 +340,19 @@ describe('workflows deps', () => {
       ).toEqual({ structuredContent: { person: { id: null }, onCall: null }, content: null })
     })
 
+    it('keeps the declared fields of a whole read beside a nested one', async () => {
+      expect(
+        await depsMock('<oncall.structuredContent> <oncall.structuredContent.onCall>')
+      ).toEqual({
+        structuredContent: {
+          role: null,
+          person: { id: null },
+          shifts: [{ start: null }],
+          onCall: null,
+        },
+      })
+    })
+
     it('keeps the read-path skeleton when the operation declares no schema', async () => {
       expect(
         await depsMock('return <oncall.structuredContent>', { server: 'server-1', tool: 'on_call' })

apps/sim/lib/mothership/agent-cli/engines/deps.ts

@@ -122,38 +122,60 @@ function skeletonFromDeclaredOutput(node: unknown, depth = 0): unknown {
   return null
 }
 
+/** A dependency path as the segments the mock skeleton is built from. */
+function pathSegments(path: string): string[] {
+  return path
+    .split('.')
+    .filter(Boolean)
+    .flatMap((part) => {
+      const { property, pathParts } = splitLeadingBracketPath(part)
+      return [property, ...pathParts]
+    })
+}
+
 /**
- * Replaces each null leaf of an MCP block's mocked `structuredContent` with the
- * skeleton its operation's declared output schema gives at that path, so a mock
- * of a declaring operation starts from the reply's real fields rather than from
- * whatever names the consuming block guessed. A leaf the schema does not declare
- * stays null.
+ * Fills an MCP block's mocked `structuredContent` from its operation's declared
+ * output schema, so a mock of a declaring operation starts from the reply's real
+ * fields rather than from whatever names the consuming block guessed. Where the
+ * consumer reads a value whole, every declared field below it is added beside
+ * the ones it reads by name; an undeclared path it reads stays as read.
  */
 function fillDeclaredStructuredContent(
   mock: Record<string, unknown>,
-  block: Record<string, unknown> | undefined
+  block: Record<string, unknown> | undefined,
+  paths: readonly string[]
 ): void {
   if (block?.type !== 'mcp' || !Object.hasOwn(mock, MCP_STRUCTURED_CONTENT_OUTPUT)) return
   // An invalid mode makes resolveMcpBlockConfig throw, which reads as no typed output.
   const modes = toRecord(toRecord(block.data).canonicalModes) as CanonicalModeOverrides
   const outputs = getMcpStructuredContentOutputs(toRecord(block.subBlocks), modes)
   const declared = outputs?.[MCP_STRUCTURED_CONTENT_OUTPUT]
   if (!declared) return
+  const readWhole = new Set(paths.map((path) => pathSegments(path).join('.')))
 
-  const fill = (value: unknown, node: unknown): unknown => {
+  const fill = (value: unknown, node: unknown, at: string): unknown => {
     if (value === null) return skeletonFromDeclaredOutput(node)
     if (!isRecordLike(node)) return value
-    if (Array.isArray(value)) return value.map((item) => fill(item, node.items))
+    if (Array.isArray(value))
+      return value.map((item, index) => fill(item, node.items, `${at}.${index}`))
     if (!isRecordLike(value) || !isRecordLike(node.properties)) return value
     const properties = node.properties
-    return Object.fromEntries(
-      Object.entries(value).map(([key, child]) => [
-        key,
-        Object.hasOwn(properties, key) ? fill(child, properties[key]) : child,
-      ])
-    )
+    const read = Object.entries(value).map(([key, child]): [string, unknown] => [
+      key,
+      Object.hasOwn(properties, key) ? fill(child, properties[key], `${at}.${key}`) : child,
+    ])
+    const added = readWhole.has(at)
+      ? Object.entries(properties)
+          .filter(([key]) => !Object.hasOwn(value, key))
+          .map(([key, child]): [string, unknown] => [key, skeletonFromDeclaredOutput(child)])
+      : []
+    return Object.fromEntries([...added, ...read])
   }
-  mock[MCP_STRUCTURED_CONTENT_OUTPUT] = fill(mock[MCP_STRUCTURED_CONTENT_OUTPUT], declared)
+  mock[MCP_STRUCTURED_CONTENT_OUTPUT] = fill(
+    mock[MCP_STRUCTURED_CONTENT_OUTPUT],
+    declared,
+    MCP_STRUCTURED_CONTENT_OUTPUT
+  )
 }
 
 interface DepView {
@@ -330,7 +352,11 @@ export const workflowDepsCommand: AgentCliEngine = {
     // parent it never reads at all — run_block refuses to start without them.
     const shapes = blockDeps.map((d) => {
       const shape = skeletonFromPaths(d.paths ?? [])
-      fillDeclaredStructuredContent(shape.value, d.blockId ? blocks[d.blockId] : undefined)
+      fillDeclaredStructuredContent(
+        shape.value,
+        d.blockId ? blocks[d.blockId] : undefined,
+        d.paths ?? []
+      )
       return { name: d.blockName ?? d.blockId ?? d.token, ...shape }
     })
     const mock: Record<string, Record<string, unknown>> = Object.fromEntries(

apps/sim/lib/workflows/triggers/mock-payload.test.ts

@@ -0,0 +1,15 @@
+import { describe, expect, it } from 'vitest'
+import { generateMockPayloadFromOutputsDefinition } from '@/lib/workflows/triggers/mock-payload'
+
+describe('generateMockPayloadFromOutputsDefinition', () => {
+  it('samples a declared __proto__ field as a field, never as the prototype', () => {
+    const outputs = JSON.parse(
+      '{"structuredContent":{"type":"json","properties":{"__proto__":{"type":"json","properties":{"polluted":{"type":"boolean"}}},"role":{"type":"string"}}}}'
+    )
+    const sample = generateMockPayloadFromOutputsDefinition(outputs)
+    const structured = sample.structuredContent as Record<string, unknown>
+    expect(Object.getPrototypeOf(structured)).toBe(Object.prototype)
+    expect(Object.keys(structured)).toEqual(['__proto__', 'role'])
+    expect(Object.hasOwn(structured, '__proto__')).toBe(true)
+  })
+})

apps/sim/lib/workflows/triggers/mock-payload.ts

@@ -47,6 +47,24 @@ function generateMockValue(type: string, _description?: string, fieldName?: stri
   }
 }
 
+/**
+ * Samples each declared field as an own property. `fromEntries` defines rather
+ * than assigns, so a field named `__proto__` (an MCP output schema may declare
+ * one) stays a field instead of replacing the sample's prototype.
+ */
+function sampleFields(
+  fields: Record<string, unknown>,
+  depth: number,
+  maxDepth: number
+): Record<string, unknown> {
+  return Object.fromEntries(
+    Object.entries(fields).map(([key, field]) => [
+      key,
+      processOutputField(key, field, depth + 1, maxDepth),
+    ])
+  )
+}
+
 /**
  * Recursively processes nested output structures, expanding JSON-Schema-style
  * objects/arrays that define `properties` or `items` instead of returning
@@ -75,11 +93,7 @@ function processOutputField(key: string, field: unknown, depth = 0, maxDepth = 1
       typedField.properties &&
       typeof typedField.properties === 'object'
     ) {
-      const nestedObject: Record<string, unknown> = {}
-      for (const [nestedKey, nestedField] of Object.entries(typedField.properties)) {
-        nestedObject[nestedKey] = processOutputField(nestedKey, nestedField, depth + 1, maxDepth)
-      }
-      return nestedObject
+      return sampleFields(typedField.properties, depth, maxDepth)
     }
 
     if (typedField.type === 'array' && typedField.items && typeof typedField.items === 'object') {
@@ -91,11 +105,7 @@ function processOutputField(key: string, field: unknown, depth = 0, maxDepth = 1
   }
 
   if (isRecordLike(field)) {
-    const nestedObject: Record<string, unknown> = {}
-    for (const [nestedKey, nestedField] of Object.entries(field)) {
-      nestedObject[nestedKey] = processOutputField(nestedKey, nestedField, depth + 1, maxDepth)
-    }
-    return nestedObject
+    return sampleFields(field, depth, maxDepth)
   }
 
   return null