fix(browserstack-service): omit unset accessibility config

[kbrooks]

Summary

• stop treating an unset BrowserStack accessibility option as a nullable value
• avoid propagating accessibility: null through BrowserStack service config and product-map metadata
• preserve explicit accessibility enablement when it is actually configured

Problem

In WDIO v9 BrowserStack service flows, sessions can fail before creation with an error like:

WebDriverError: The property "#/alwaysMatch/bstack:options/accessibility" of type NilClass did not match one or more of the following types: boolean, string

We traced this to wdio-browserstack-service carrying accessibility state as boolean | null and then serializing that unset state into BrowserStack CLI/session config as accessibility: null.

The failure was reproducible in BrowserStack-backed Selenium preprod runs even when the user config did not set any accessibility option.

Root cause

The regression appears to come from the v9 accessibility auto-enable path introduced in a0bc710 (Auto enable accessibility [v9]).

That change introduced nullable accessibility state and propagated it through:

• BrowserStackConfig.accessibility
• launcher _accessibilityAutomation
• build start product-map/config generation

Using undefined for the unset case is safer here because it omits the field instead of sending null to BrowserStack.

Fix

• make the stored accessibility config optional instead of boolean | null
• remove the default accessibility: false option from DEFAULT_OPTIONS
• avoid writing nullable accessibility state back into launcher/config state
• keep product maps typed to allow undefined when accessibility is not configured

[xxshubhamxx]

@christian-bromann Could you review and merge this PR?

[dprevost-LMI]

Hey @kbrooks (and @wswebcreation), if I'm not mistaken, this PR is breaking npm run setup on main with the below.
I tested a reverted commit, and it seemed to work, but fixing the issue would be better. I did not take the time to understand the situation.

> @wdio/browser-runner@9.27.1 build:copy:js /Users/webdriverio/packages/wdio-browser-runner
> sed '$d' ./node_modules/mocha/mocha.js > ./build/third_party/mocha.js

[@wdio/browser-runner] ✅ Successfully ran build script for @wdio/browser-runner: "run-s build:*"
/Users/webdriverio/node_modules/.pnpm/esbuild@0.27.3/node_modules/esbuild/lib/main.js:1467
  let error = new Error(text);
              ^

Error: Build failed with 1 error:
error: [@wdio/browserstack-service] Failed to generate d.ts files: TypeScript compilation failed with code 2
src/instrumentation/funnelInstrumentation.ts(143,9): error TS2322: Type '{ [key: string]: boolean | undefined; }' is not assignable to type '{ [key: string]: boolean; }'.
  'string' index signatures are incompatible.
    Type 'boolean | undefined' is not assignable to type 'boolean'.
      Type 'undefined' is not assignable to type 'boolean'.
src/launcher.ts(975,66): error TS2322: Type '{ [key: string]: boolean | undefined; }' is not assignable to type '{ [key: string]: boolean; }'.
  'string' index signatures are incompatible.
    Type 'boolean | undefined' is not assignable to type 'boolean'.
      Type 'undefined' is not assignable to type 'boolean'.
src/launcher.ts(995,29): error TS2322: Type '{ [key: string]: boolean | undefined; }' is not assignable to type '{ [key: string]: boolean; }'.
  'string' index signatures are incompatible.
    Type 'boolean | undefined' is not assignable to type 'boolean'.
      Type 'undefined' is not assignable to type 'boolean'.
src/launcher.ts(1014,25): error TS2322: Type '{ [key: string]: boolean | undefined; }' is not assignable to type '{ [key: string]: boolean; }'.
  'string' index signatures are incompatible.
    Type 'boolean | undefined' is not assignable to type 'boolean'.
      Type 'undefined' is not assignable to type 'boolean'.
src/launcher.ts(1033,99): error TS2322: Type '{ [key: string]: boolean | undefined; }' is not assignable to type '{ [key: string]: boolean; }'.
  'string' index signatures are incompatible.
    Type 'boolean | undefined' is not assignable to type 'boolean'.
      Type 'undefined' is not assignable to type 'boolean'.
src/launcher.ts(1052,25): error TS2322: Type '{ [key: string]: boolean | undefined; }' is not assignable to type '{ [key: string]: boolean; }'.
  'string' index signatures are incompatible.
    Type 'boolean | undefined' is not assignable to type 'boolean'.
      Type 'undefined' is not assignable to type 'boolean'.
src/launcher.ts(1071,21): error TS2322: Type '{ [key: string]: boolean | undefined; }' is not assignable to type '{ [key: string]: boolean; }'.
  'string' index signatures are incompatible.
    Type 'boolean | undefined' is not assignable to type 'boolean'.
      Type 'undefined' is not assignable to type 'boolean'.
src/util.ts(403,67): error TS2345: Argument of type 'boolean | null' is not assignable to parameter of type 'boolean | undefined'.
  Type 'null' is not assignable to type 'boolean | undefined'.

    at failureErrorWithLog (/Users/webdriverio/node_modules/.pnpm/esbuild@0.27.3/node_modules/esbuild/lib/main.js:1467:15)
    at /Users/webdriverio/node_modules/.pnpm/esbuild@0.27.3/node_modules/esbuild/lib/main.js:926:25
    at /Users//webdriverio/node_modules/.pnpm/esbuild@0.27.3/node_modules/esbuild/lib/main.js:1345:9
    at process.processTicksAndRejections (node:internal/process/task_queues:103:5) {
  errors: [Getter/Setter],
  warnings: [Getter/Setter]
}

Node.js v24.11.1

[kbrooks]

Yeah it got merged with a failing check somehow so it's probably broken

[kbrooks]

@dprevost-LMI I have a fix here #15262