fix(executor): follow drive#operation downloadUri for large Shared-Drive downloads

[TheSecMaven]

Problem

A ~12MB native (non-Google) file living in a Shared Drive, downloaded with the
drive.files.download command and --output, silently produces no file. Repeated
attempts against the same file oscillated between:

• Most attempts: 500 backendError — likely transient on Google's side, not addressed
  by this PR (see below).
• Occasionally: HTTP 200 with a JSON body shaped like a drive#operation:

  {
    "kind": "drive#operation",
    "response": {
      "downloadUri": "https://www.googleapis.com/drive/v3/files/FAKE_FILE_ID_1?alt=media&source=downloadUrl",
      "partialDownloadAllowed": true
    }
  }

  This is Drive telling the client "the bytes aren't in this response, fetch them from
  downloadUri." The executor had no branch for this shape — it treated the envelope
  as an ordinary JSON response, printed it, and never wrote anything to --output, with
  no error at all.

Related: #789, #727 (also reports files.download returning 500 backendError "on
ordinary files," and its own comment confirms drive files get --params '{"fileId":"...","alt":"media"}' --output out.png works as a reliable workaround —
worth documenting as the recommended path for plain binary fetches regardless of this
fix). #727 also has a second-platform report of the same root cause surfacing as 411 Length Required on arm64, which is consistent with files.download being a distinct,
less-exercised code path from files.get?alt=media.

This reimplements and extends the approach from the earlier #805 (closed by the
72-hour stale-bot before review, not on the merits — the review comment on it was
positive) with additional negative-case tests.

Fix

• extract_google_download_uri recognizes a drive#operation response (kind == "drive#operation") carrying a downloadUri/downloadUrl at any of the shapes
  actually observed, and rejects (errors, does not silently ignore) any such URI whose
  host isn't Google's own — following an arbitrary redirect from a JSON response body
  and attaching our auth to it would be a real SSRF/credential-leak vector otherwise.
• When drive.files.download returns one of these envelopes and --output was given,
  the executor now follows the downloadUri with a second, restricted request and
  hands the real response off to the existing binary-file writer, instead of treating
  the envelope as the final output.
• The follow-up request only attaches our bearer token to the exact hosts that expect
  one (googleapis.com, www.googleapis.com, storage.googleapis.com); a signed URL
  (query string carries GoogleAccessId/Signature/X-Goog-*) gets neither the quota
  header nor the bearer token, since it already carries its own auth.

On the 500s

Several of the repro attempts got a 500 backendError with no envelope at all. I did
not add retry/backoff for this — it isn't clearly this client's bug (issue #727 shows
the same root cause surfacing as a different error, 411 Length Required, on a
different architecture, which points at something inconsistent server-side or in how
this specific RPC constructs its request rather than at response handling). Happy to
add bounded retry-with-backoff on files.download specifically if a maintainer wants
it, but didn't want to bundle a guess at that into a response-parsing fix.

On the S3 suggestion

A workaround using an S3 (or S3-compatible) bucket as an intermediate staging target
for large/flaky binary downloads was floated while investigating this. Not used here —
this CLI has no existing AWS dependency, and the actual bug is that the client doesn't
follow a URI Google's own API is already handing it; adding a second cloud provider's
SDK to work around that would be solving the wrong layer. Noting it here in case it's
useful context for a different, unrelated feature request.

Tests

21 new unit tests: URI extraction from the operation envelope (including a same-shaped
plain-JSON file that must NOT be treated as an operation), host validation (Google
hosts allowed, look-alike/non-https/userinfo-bearing hosts rejected), the
googleusercontent.com-allowed-but-never-bearer-token asymmetry, signed-vs-unsigned
URI detection, and header construction for both the fallback quota-project header and
the download follow-up request. Full crate suite: cargo test -p google-workspace-cli
— 715 passed, 0 failed. cargo clippy --all-targets and cargo fmt --check both clean
on the new code.

[changeset-bot]

🦋 Changeset detected

Latest commit: 868a408

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@googleworkspace/cli	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.