Fix flaky plugin hook env test

[abhinav-oai]

The test was flaky because it was checking the right thing in a roundabout way.

What it wanted to prove:

• plugin hooks receive the right environment variables.

What it actually did:

1. Run a plugin hook.
2. Have that hook write those env vars into a temporary env.json file.
3. After the hook finished, read env.json back from disk.

On Windows, that last file was sometimes not there when the test tried to read it, so the test failed with read env log: file not found. The hook system itself was not what the test failure was directly proving; the test was failing on the extra filesystem side effect it introduced.

The fix is to stop using a temp file as the proof mechanism. The hook now prints the env values in its normal structured output, and the test asserts on the output that the hook engine already captures. So we still verify the same behavior, but without depending on a separate file being created and read back correctly on Windows.