fix: declare browser.setCustomTags on WebdriverIO.Browser type (SDK-6882)

[Bhargavi-BS]

Port of harshit-browserstack/webdriverio#5 to the standalone repo.

What

Declares browser.setCustomTags(key, value) on the global WebdriverIO.Browser interface so TypeScript consumers of @wdio/browserstack-service can call it without a compile error.

Why

Jira SDK-6882: a WebdriverIO + Mocha (TypeScript) customer on @wdio/browserstack-service@9.29.1 hit:

Property 'setCustomTags' does not exist on type 'Browser'.

The command works at runtime (the service attaches it, and the customer's test calling it passed) — the failure is compile-time only. The setCustomTags/a11y declarations live in src/@types/bstack-service-types.d.ts but that file uses declare namespace and is pulled in only via /// <reference path> from internal source, so it is never emitted into the shipped build/index.d.ts (the package types entry). Consumers therefore receive no setCustomTags on WebdriverIO.Browser.

Fix

Add setCustomTags to the WebdriverIO.Browser augmentation in the declare global block of src/index.ts, which is emitted to build/index.d.ts and delivered to consumers:

setCustomTags: (key: string, value: string) => Promise<void>

Merges cleanly with the existing ambient declaration (identical signature). Runtime behavior unchanged.

Port notes (drift vs the fork PR)

The fork PR was authored against webdriverio/webdriverio@main, where the declare global block has no interface Browser, so it added a new one. This repo's main already ships an interface Browser augmentation in src/index.ts (the a11y methods — getAccessibilityResultsSummary, getAccessibilityResults, performScan, startA11yScanning, stopA11yScanning), so the setCustomTags member is added to that existing block instead of declaring a second one. This also means the fork PR's noted follow-up ("the a11y methods share the same non-shipping cause") is already addressed in this repo for those methods.

Verification

• npx tsc --noEmit -p packages/browserstack-service exits 0 (after npm run generate) — no duplicate-identifier conflict with the ambient bstack-service-types.d.ts declaration.
• Full vitest suite in packages/browserstack-service: 1004 passed / 0 failed (identical to base main — type-only change).
• On the original fork PR, a minimal consumer project reproduced the exact TS2339 against the pristine published 9.29.1 tgz and compiled clean against the patched build.

🤖 Generated with Claude Code

[dandonarahul2002]

rest lgtm