Sanitize hostile ability input schemas before tool conversion

src/tool-schema.test.ts

@@ -0,0 +1,90 @@
+/**
+ * Tool Schema Conversion Tests
+ *
+ * Regression coverage for hostile/malformed remote input schemas.
+ * PHP dashboards serialize empty associative arrays as JSON arrays, so a
+ * no-input ability can arrive with `properties: []`. Passing that through
+ * invalidates the entire tools/list response for spec-compliant MCP clients
+ * (the official SDK rejects it with a zod error), which leaves the server
+ * connected but with zero usable tools.
+ */
+
+import { describe, it, expect } from 'vitest';
+import { abilityToTool } from './tool-schema.js';
+import type { Ability } from './abilities.js';
+
+function makeAbility(overrides: Partial<Ability> = {}): Ability {
+  return {
+    name: 'mainwp/get-network-snapshot-v1',
+    label: 'Get Network Snapshot',
+    description: 'Returns a snapshot of the network.',
+    category: 'mainwp-sites',
+    ...overrides,
+  };
+}
+
+describe('abilityToTool input schema sanitization', () => {
+  it('coerces array-typed properties (PHP empty array) to an empty object', () => {
+    // JSON.parse round-trip mirrors how the payload actually arrives
+    const ability = makeAbility({
+      input_schema: JSON.parse('{"type":"object","properties":[]}') as Record<string, unknown>,
+    });
+
+    const tool = abilityToTool(ability, 'mainwp');
+
+    expect(Array.isArray(tool.inputSchema.properties)).toBe(false);
+    expect(tool.inputSchema.properties).toEqual({});
+    expect(tool.inputSchema.required).toEqual([]);
+  });
+
+  it('coerces non-object properties to an empty object', () => {
+    const ability = makeAbility({
+      input_schema: { type: 'object', properties: 'bogus' },
+    });
+
+    const tool = abilityToTool(ability, 'mainwp');
+
+    expect(tool.inputSchema.properties).toEqual({});
+  });
+
+  it('coerces a non-array required field to an empty array', () => {
+    const ability = makeAbility({
+      input_schema: { type: 'object', properties: {}, required: 'site_id' },
+    });
+
+    const tool = abilityToTool(ability, 'mainwp');
+
+    expect(tool.inputSchema.required).toEqual([]);
+  });
+
+  it('drops non-string entries from required', () => {
+    const ability = makeAbility({
+      input_schema: {
+        type: 'object',
+        properties: { site_id: { type: 'integer', description: 'Site ID.' } },
+        required: ['site_id', 7, null, { bad: true }],
+      },
+    });
+
+    const tool = abilityToTool(ability, 'mainwp');
+
+    expect(tool.inputSchema.required).toEqual(['site_id']);
+  });
+
+  it('preserves well-formed object properties unchanged', () => {
+    const ability = makeAbility({
+      input_schema: {
+        type: 'object',
+        properties: { site_id: { type: 'integer', description: 'Site ID.' } },
+        required: ['site_id'],
+      },
+    });
+
+    const tool = abilityToTool(ability, 'mainwp');
+
+    expect(tool.inputSchema.properties).toEqual({
+      site_id: { type: 'integer', description: 'Site ID.' },
+    });
+    expect(tool.inputSchema.required).toEqual(['site_id']);
+  });
+});

src/tool-schema.ts

@@ -31,8 +31,19 @@ function convertInputSchema(ability: Ability): Tool['inputSchema'] {
   // The abilities API uses JSON Schema, which is compatible with MCP
   // We just need to ensure it has the required structure
   // Cast to the expected MCP SDK type
-  const properties = (schema.properties || {}) as { [key: string]: Record<string, unknown> };
-  const required = (schema.required as string[]) || [];
+  //
+  // PHP dashboards serialize empty associative arrays as [] — an array-typed
+  // `properties` (or malformed `required`) invalidates the whole tools/list
+  // response for spec-compliant clients, so coerce anything non-conforming.
+  const rawProperties = schema.properties;
+  const properties = (
+    rawProperties && typeof rawProperties === 'object' && !Array.isArray(rawProperties)
+      ? rawProperties
+      : {}
+  ) as { [key: string]: Record<string, unknown> };
+  const required = Array.isArray(schema.required)
+    ? schema.required.filter((entry): entry is string => typeof entry === 'string')
+    : [];
 
   // Backfill missing descriptions from parameter names.
   // Some upstream abilities omit descriptions; LLMs need them for accurate tool use.