[dhruva-vapi]

Related: PRISM-1083 (Zeals)

Problem

About 40% of Zeals' web-widget calls end with assistant-did-not-receive-customer-audio.

vapi.start() sends POST /call/web before it creates the Daily call object, and the mic is only requested later, inside join(). As a result, a backend call is created and billed even when the user denies or ignores the mic prompt. The backend then times out after customerJoinTimeoutSeconds (15s by default).

Fix

start():
  track = await microphoneAcquire()   // getUserMedia, before POST /call/web
  webCall = POST /call/web
  Daily.createCallObject({ audioSource: track, ... })   // reuse the track, no second acquisition

• On failure (denied, no device, empty stream, mediaDevices unavailable): no backend call is made. start() emits call-start-failed with stage: 'microphone-preflight' and error with type: 'microphone-preflight-<DOMException name>', then returns null.
• Device selection: a device-ID audioSource becomes { deviceId: { exact } }. A caller-supplied MediaStreamTrack is reused as-is and never stopped by the SDK.
• Track cleanup: the SDK stops its own track in cleanup(), in stop(), and on API or join failure.
• Pending prompt: stop() cancels it (AbortError), and a track granted late is stopped. A concurrent second start() returns null. There's no timeout; stop() is the way out.
• Opt-out: on by default. Disable it with vapi.start(assistant, ..., { microphonePreflightEnabled: false }) (StartCallOptions).
• Cleanup of an existing call object now happens before preflight instead of after the API call.

Verification

Tested in real Chrome with a fake mic device and native permission prompts, comparing published @vapi-ai/web@3.0.0 against this branch. I checked each attempt via GET /call.

Scenario	Backend call created?	Result
3.0.0, mic denied	Yes	silence-timed-out
3.0.0, prompt ignored >20s	Yes	assistant-did-not-receive-customer-audio
This PR, mic denied	No	microphone-preflight-NotAllowedError
This PR, mic allowed	Yes	greeting played, stop() worked
This PR, prompt pending, then stop()	No	microphone-preflight-AbortError, no hang

New __tests__/microphone-preflight.test.ts. npm run build passes and npm test passes 73/73.

Not tested: a physical mic, iOS Safari, iframe mic policy, and the opt-out path in a browser (the opt-out has a unit test).

The widgets (client-sdk-html-script-tag, client-sdk-react) pin SDK 2.x, so they need a version bump to pick this up.

Link to Devin session: https://app.devin.ai/sessions/f0c8f585b41d4cbaa0459bfc8d22e211
Open in Devin Desktop: https://app.devin.ai/desktop/session/f0c8f585b41d4cbaa0459bfc8d22e211?variant=devin

[devin-ai-integration]

I'll fix CI failures and address comments from users with write access that start with 'Devin'.

• Disable automatic comment, CI, and merge conflict monitoring

[shubham-vapiai]

LGTM