VERIFYFIRST // file-on-disk
The file's contents — You read the config, the stylesheet, or the source and confirmed it says the right thing.

WHAT IT CAPTURES
  Authored intent, at the moment you read it.

WHAT IT CANNOT SEE
  - What a running process actually loaded, which may predate your edit.
  - What overrode it later, in any last-writer-wins system.
  - Whether the file is the one being served, as opposed to one with the same name elsewhere.
  - Whether a plausible-looking artifact is the correct artifact.

KNOWN FAILURES (5)

  NS-003  A later cascade rule silently revokes position: fixed
    reads as   The element is declared `position: fixed` in the stylesheet. Conclusion drawn: the browser or the viewport is at fault.
    actually   A rule added later for an unrelated purpose (`main, .nav, .colophon { position: relative }`) matched the same element and won on document order.
    check      getComputedStyle(el).position — the resolved value, never the authored one.

  NS-006  Scraping the largest asset returns a recommendation, not the subject
    reads as   A parser extracts an image from the page and it is a valid, plausible image. Conclusion drawn: extraction succeeded.
    actually   The page embeds related items alongside the subject. Ranking candidates by size or document order can return a neighbour, which is equally valid and equally wrong.
    check      Prefer the canonical marker the page declares about itself (og:image, canonical link, structured data) over any heuristic ranking of candidates.

  NS-023  sshd takes the first value for a keyword, so an appended directive loses to an include
    reads as   /etc/ssh/sshd_config ends with `PasswordAuthentication no`, and sshd reloaded without error. Conclusion drawn: password logins are disabled.
    actually   The man page states that unless noted otherwise, for each keyword the first obtained value will be used. On a stock Ubuntu image `Include /etc/ssh/sshd_config.d/*.conf` sits at line 12 of a 131-line file, so a drop-in such as 50-cloud-init.conf that sets the same keyword is read first and wins. The line appended at the bottom is parsed and discarded.
    check      `sudo sshd -T | grep -i passwordauthentication` prints the effective merged value the daemon will use, which differs from the authored line whenever an earlier occurrence won. Run it with root privileges: as an unprivileged user it silently omits unreadable drop-ins.

  NS-024  Bidirectional control characters make source read differently than it compiles
    reads as   A reviewer reads the diff and the early return is plainly inside a comment. Conclusion drawn: the change is inert.
    actually   Unicode bidirectional overrides (U+202A to U+202E, U+2066 to U+2069) reorder the display of tokens without changing their logical order. Compilers and interpreters adhere to the logical ordering of source code, not the visual order, so the code executed is not the code rendered. Catalogued as CVE-2021-42574, with a homoglyph variant as CVE-2021-42694.
    check      Search for the characters instead of reading the text: `grep -rlP '[\x{202A}-\x{202E}\x{2066}-\x{2069}]' path/` names files containing them and prints nothing for files that do not. Verified against a planted sample and a clean file.

  NS-025  A JSON integer above 2^53 is silently rounded when parsed as a double
    reads as   The response contains `"id": 10765432100123456789`; the parsed object has an id of the right shape and it round-trips through the code. Conclusion drawn: the identifier was carried through intact.
    actually   JavaScript parses JSON numbers as IEEE 754 doubles. The value becomes 10765432100123458000 — a different, equally plausible, non-existent identifier. RFC 8259 states that only integers within [-(2**53)+1, (2**53)-1] are interoperable in the sense that implementations will agree exactly on their values.
    check      `Number.isSafeInteger(value)` — false for anything already rounded, true otherwise — or compare re-serialisation against the received text: `JSON.stringify(JSON.parse(s)) === s`. Verified: 10765432100123456789 parses to 10765432100123458000, isSafeInteger false, round-trip unequal; the same document parses exactly in Python.

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Full registry: https://verifyfirst.dev/registry.json
This page:     https://verifyfirst.dev/file-on-disk/
CC0-1.0. Every entry observed, none hypothetical.