Reco counts download used text/csv and LF instead of text/plain and CRLF

[adamtheturtle]

Found by probing the endpoint against real Vuforia with a throwaway database, which #3359 and #3360 were waiting to be able to do. Both are fixed locally on adamtheturtle/create-vws-web-tools-issue, but are recorded here so that the defects and their evidence are not lost in a branch.

The bugs

The mock served a generated reco counts report with the wrong content type and the wrong line ending.

	Mock before	Real Vuforia
Content-Type	text/csv	text/plain
Header row	target_id,reco_count\n	target_id,reco_count\r\n

Both matter to a caller. Code which branches on the content type, or which splits on \r\n, or which compares a downloaded body byte for byte, passes against the mock and behaves differently against real Vuforia.

Evidence

Requesting a report for the current month and fetching the returned presigned URL:

status: 200
headers: {..., 'Content-Type': 'text/plain', 'Content-Length': '22',
 'Server': 'AmazonS3', 'x-amz-server-side-encryption': 'AES256', ...}
body: b'target_id,reco_count\r\n'

Note Content-Length: 22, which is the 20 characters of the header row plus a carriage return and a line feed.

Real Vuforia serves the report from S3 rather than from the VWS API, which is why the content type is S3's default rather than a CSV type. The bucket in this observation was guacamole-targetstore-production-targets.s3.us-west-1.amazonaws.com.

The report contained only the header row, which confirms the mock's shape for a database with no recognitions. The database was created seconds earlier and had no targets, so an empty report is expected. Whether a row for a target with recognitions also uses \r\n is untested, and is part of #3356.

The fix

• src/mock_vws/reco_counts.py: the header row now ends \r\n.
• src/mock_vws/_reco_counts_web_api.py: the download response now has a text/plain content type.
• tests/mock_vws/test_reco_counts_report.py: TestDownloadReport asserts both.

Why the mock got this wrong

The endpoint was added in #3357 without being able to reach real Vuforia, because a request needs a database ID that the test credentials did not carry. text/csv and \n were the natural guesses for a file described in the documentation as a CSV report. differences-to-vws.rst did flag the download response headers and the CSV content as unverified, so the guesses were labelled, but a labelled guess is still a wrong answer for anyone who trusted it.

Acceptance criteria

• The fixes above are merged.
• differences-to-vws.rst no longer lists the download content type or the CSV content as unverified, since both have now been observed.