feat(e2b): support token acquisition via GET /sandboxes/{id}

[vaaandark]

Summary

Enable E2B backend to acquire access tokens from the GET /sandboxes/{id} endpoint, unifying token recovery behavior across both Cloud and E2B backends.

Related Issues

N/A

Changes

• internal/client/e2b.go

  • Rewrite GetInstance to call GET /sandboxes/{id} directly (instead of iterating via ListInstances), parsing the envdAccessToken field from the response
  • Rewrite AcquireToken to retrieve token via GetInstance instead of returning an "unsupported" error

• cmd/sandbox_helper.go

  • Remove E2B-specific error branch in GetCachedTokenOrAcquire, unifying the acquire flow for both backends

• cmd/browser.go

  • Remove E2B-specific error handling in acquireInstanceToken

• internal/client/interface.go

  • Update AcquireToken interface doc comment to reflect E2B support

Motivation

Previously, the E2B backend only returned the access token once during CreateInstance. If the local token cache (~/.ags/tokens.json) was lost, the instance became unusable and had to be recreated. The GET /sandboxes/{id} API actually includes the envdAccessToken field in its response, so tokens can be re-acquired at any time.

Testing

• Verified GET /sandboxes/{id} returns envdAccessToken for running instances
• go build ./... passes with no errors

[keithfx999]

LGTM

[keithfx999]

LGTM