`PLATFORM_ARTIST_PATTERNS` (extension/lib/platforms.js) and
`_PLATFORM_PATTERNS` (extension_service.py) are two hand-kept copies of one
table whose only guard was the comment "keep in sync by hand; reviewers catch
drift" — the same guarantee manifest.json had before #3069, where deviantart
sat in the manifest for seven weeks after the product dropped it.
Drift here is worse than the manifest case, because the two copies gate
opposite halves of ONE interaction: the JS copy decides whether the "Add to
FC" button appears, the Python copy decides whether the resulting POST is
accepted. JS looser than Py shows a button that 400s; Py looser than JS
silently never offers a button for a URL the backend would take. #1485 (the
Patreon /c/ and /cw/ shapes) was the second of those, and its fix had to be
applied to both files by hand.
The two-runtimes objection to a shared SOURCE file is fair, so this tests the
invariant instead of the source. `extension/test/artist-url-samples.json` is
one table of 25 URL samples — match (with the expected slug) and no_match,
each with a `why` — read by BOTH suites and asserted against each one's own
copy of the patterns. Neither runtime imports the other; a change to one copy
alone turns the other runtime's suite red.
Both halves also assert their own coverage: the sample platforms must equal
the platforms that actually have an artist pattern, and every platform must
have samples in both directions. Without that, deleting a platform's samples
would make the guard pass by testing less. Discord is deliberately in neither
table — it is channel-based and has no creator page to put a button on.
The no_match half asserts `_derive` RAISES rather than merely missing the
platform: it tries every pattern in turn, so a nav page some other platform's
pattern happened to swallow would still be accepted by the backend — the same
defect wearing a different platform name.
Samples live under extension/test/ because that path is excluded from both
the XPI file set and the extension version derivation (packaging.sh:
NOT_PACKAGED_TRACKED and NOT_VERSION_RELEVANT both carry `test/**`), so
adding samples ships no bytes and forces no re-sign.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LVjrnpQjRgHdvq95rASoiR
bvandeusenandClaude Opus 5
bd92fb46b3