Unable to get custom functions and rules working

[erunion]

I am running 0.17.0 and am having difficulty getting custom functions and rulesets with those working. I have followed the tutorial on https://quobix.com/vacuum/api/custom-javascript-functions/#tutorial and here's my ruleset YAML:

extends: [[vacuum:oas, off]]
rules:
  sample-paths-rule:
    description: Load a custom function that checks for a single path
    severity: error
    recommended: true
    formats: [oas2, oas3]
    given: $.paths
    then:
      function: checkSinglePath
    howToFix: use a spec with only a single path defined.

I have placed checkSinglePath.js into a ./vacuum directory and am running Vacuum with the following:

npx vacuum lint --no-clip --ruleset vacuum.yaml -d -f ./vacuum openapi-v2-public.json --show-rules --no-style


██╗   ██╗ █████╗  ██████╗██╗   ██╗██╗   ██╗███╗   ███╗
██║   ██║██╔══██╗██╔════╝██║   ██║██║   ██║████╗ ████║
██║   ██║███████║██║     ██║   ██║██║   ██║██╔████╔██║
╚██╗ ██╔╝██╔══██║██║     ██║   ██║██║   ██║██║╚██╔╝██║
 ╚████╔╝ ██║  ██║╚██████╗╚██████╔╝╚██████╔╝██║ ╚═╝ ██║
  ╚═══╝  ╚═╝  ╚═╝ ╚═════╝ ╚═════╝  ╚═════╝ ╚═╝     ╚═╝


version: 0.17.0 | compiled: Sun, 08 Jun 2025 18:08:07 UTC
🔗 https://quobix.com/vacuum | https://github.com/daveshanley/vacuum


INFO: Located custom javascript function: 'checkSinglePath'
INFO: Loaded 1 custom function(s) successfully.
The following rules are being used:

►   [1] oas3-missing-example: (Check schemas, headers, parameters and media types all have examples present.)
►   [2] oas3-api-servers: (Validate API server definitions)
►   [3] duplicated-entry-in-enum: (Check for duplicate enum entries)
►   [4] oas3-schema: (Check spec is valid OpenAPI 3)
►   [5] oas2-discriminator: (Discriminator check)
►   [6] oas-schema-check: (schemas must have a valid type defined)
►   [7] operation-operationId-unique: (Check operations for unique operationId)
►   [8] no-$ref-siblings: (Check for siblings to $ref values)
►   [9] path-item-refs: (Check path items have not used references)
►  [10] operation-tag-defined: (Check operation tags exist globally)
►  [11] oas2-parameter-description: (Check parameter description)
►  [12] path-declarations-must-exist: (Check path parameter declarations)
►  [13] operation-operationId-valid-in-url: (Check operationId is URL friendly)
►  [14] paths-kebab-case: (Path segments must be kebab-case only)
►  [15] component-description: (Check component description)
►  [16] no-ambiguous-paths: (No ambiguous paths, each path must resolve unambiguously)
►  [17] info-license-spdx: (Check license object for URL or identifier, but not both)
►  [18] path-keys-no-trailing-slash: (Check path for any trailing slashes)
►  [19] oas3-operation-security-defined: (Check operation security)
►  [20] typed-enum: (Check enum types)
►  [21] oas2-host-not-example: (Check server URLs for example.com)
►  [22] oas3-unused-component: (Check for unused components)
►  [23] no-script-tags-in-markdown: (Check descriptions for '<script>' tags)
►  [24] path-params: (Check path validity and definition)
►  [25] oas2-oneOf: (Check for invalid use of 'oneOf')
►  [26] description-duplication: (Check descriptions for duplicates)
►  [27] oas3-example-external-check: (Check schemas, headers, parameters and media types use either 'example' or 'externalValue' but not both.)
►  [28] oas3-valid-schema-example: (Check all example schemas are valid)
►  [29] operation-description: (Check operation description)
►  [30] operation-parameters: (Check operation parameters)
►  [31] operation-tags: (Check operation tags are used)
►  [32] operation-operationId: (Check operations for an operationId)
►  [33] oas2-schema: (Check schema is valid OpenAPI 2)
►  [34] oas2-api-schemes: (Check host schemes are defined)
►  [35] oas2-anyOf: (Check for invalid use of 'anyOf')
►  [36] oas2-api-host: (Check spec for 'host' value)
►  [37] no-http-verbs-in-path: (Paths cannot contain HTTP verbs as segments)
►  [38] oas2-operation-security-defined: (Check operation security)
►  [39] info-description: (Check for a specification description)
►  [40] operation-success-response: (Check operations for success response)
►  [41] oas3-parameter-description: (Check parameter description)
►  [42] no-request-body: (Check GET and DELETE methods do not accept request bodies)
►  [43] no-eval-in-markdown: (Check descriptions for  'eval()' statements)
►  [44] oas2-unused-definition: (Check for unused definitions)
►  [45] oas2-operation-formData-consume-check: (Check operation parameter 'formData' definition)
►  [46] oas2-host-trailing-slash: (Check host for trailing slash)
►  [47] path-not-include-query: (Check path excludes query string)
►  [48] oas3-no-$ref-siblings: (Check for siblings to $ref values)


INFO: Linting file 'openapi-v2-public.json' against 1 rules: https://quobix.com/vacuum/rulesets/no-rules

Have I screwed something up in the way I am configuring this custom rule?