Removes the last native dependency from the ingest path, so the server no longer
needs a per-platform/per-ABI prebuilt to thumbnail an image. Motivated by getting
the server onto hardware with no toolchain, but the ABI tax is paid on every
install — it is the same failure class lib/preflight-deps.js exists to explain.
lib/image-ops.js is the whole surface: metadata() and writeThumbnail(), which are
the only two things ingest ever asked sharp for.
Format parity holds. jpeg/png/gif/tiff/bmp are native to Jimp; webp and avif go
through @jsquash WASM, whose bundled .wasm must be compiled by hand because the
packages locate it with fetch(file://) and Node has no file:// fetch — the only
symptom otherwise is a bare "fetch failed". heic is unsupported, as it already
was: sharp advertises heif but its prebuilt libvips refuses HEVC.
#170 is preserved by a different mechanism. Jimp applies EXIF orientation at
decode and rewrites the tag to 1, so metadata() reports display dimensions and
imageDisplayDims() runs as a no-op instead of swapping W/H a second time. The
helper stays in the path so the rule keeps living in one place.
Verified: 1643/1643 tests pass, and ingest was exercised in a child process with
node_modules/sharp moved aside — jpeg, EXIF-rotated jpeg, png, webp, avif, gif
all measured and thumbnailed correctly, corrupt input still yields nulls with no
phantom thumbnail_path.
KNOWN BLOCKER, do not ship as-is: Jimp is pure JS on the main thread, where sharp
handed work to a libvips threadpool. A 12MP photo goes 65ms -> 1079ms, and the
event loop stalls for 1003ms of it (sharp: zero stalls). thumbnail-backfill.js
walks a whole library at boot, so this reproduces #240 exactly — blocked loop,
missed heartbeats, panels marked offline, reconnect churn. Needs a worker_thread
offload before this is viable; image-ops.js is the seam for it.
