This started showing up after agable@ landed https://chromium.googlesource.com/infra/infra/+/d42277eb447b0b3d7d63bb8ead7e9bd99d5b53db .

Example build: https://luci-milo.appspot.com/buildbot/chromium.infra.cron/third-party-packages-linux-amd64/1131

However, note that it's possible that this bug has been latent for a while, and is only manifesting now because agable@ fixed the build, allowing it to terminate with a SUCCESS status (I see no STEP_FAIL or STEP_EXCEPTION annotations).

The fact that this is an invalid annotation state makes me think that it is a bug in Recipe Engine.'

Actually, looking back through the builds, the last successful build and first failed build is due to this, not patch failure:
- Last successful, 10/20 @1200 PST (1055): https://uberchromegw.corp.google.com/i/chromium.infra.cron/builders/third-party-packages-linux-amd64/builds/1055
- First failed, 10/20 @1600 PDT (1056): https://uberchromegw.corp.google.com/i/chromium.infra.cron/builders/third-party-packages-linux-amd64/builds/1056

Highly suspect CL: https://chromium.googlesource.com/infra/infra/+/92b1d5f8a771f1f433bfde3e2f9b1a9b21f8c39c

This still seems like a recipe engine bug, unless that CL is doing something really funky, since recipe engine should never emit an illegal annotation state.

From the builds "stdio" link, which contains its annotations:
...
@@@STEP_LINK@stdout-->stdio@https://logs.chromium.org/v/?s=chromium%2Fbb%2Fchromium.infra.cron%2Fthird-party-packages-linux-amd64%2F1131%2F%2B%2Frecipes%2Fsteps%2Fgcloud%2F0%2Fsteps%2Fgsutil.download%2F0%2Fstdout@@@
LogDog Link [stdio]: https://logs.chromium.org/v/?s=chromium%2Fbb%2Fchromium.infra.cron%2Fthird-party-packages-linux-amd64%2F1131%2F%2B%2Frecipes%2Fsteps%2Fgcloud%2F0%2Fsteps%2Fgsutil.download%2F0%2Fstdout

remoteFailed: [Failure instance: Traceback: <type 'exceptions.ValueError'>: This operation is not supported when the cursor is set to preamble.
/home/chrome-bot/buildbot/build/third_party/twisted_10_2/twisted/spread/pb.py:516:expressionReceived
/home/chrome-bot/buildbot/build/third_party/twisted_10_2/twisted/spread/pb.py:828:proto_message
/home/chrome-bot/buildbot/build/third_party/twisted_10_2/twisted/spread/pb.py:842:_recvMessage
/home/chrome-bot/buildbot/build/third_party/twisted_10_2/twisted/spread/flavors.py:114:remoteMessageReceived