Format MIME types and sniffing

Format	Detected as (format / variant)	MIME type	Extension (hint only)	Schema / spec
.dome packed	dome / zip	application/vnd.nativemind.freedome.dome+zip	.dome	schemas/dome/1.x/dome.schema.json, 01b
.dome unpacked	dome / directory	(directory)	*.dome/	same
.zelim JSON project (variant J)	zelim / json	application/vnd.nativemind.zelim+json	.zelim	schemas/zelim/{1.0,1.1}/zelim-project.schema.json
.zelim binary quantum scene (variant B)	zelim / binary	application/vnd.nativemind.zelim	.zelim	formats/zelim-binary.ksy
.boranko 1.1 folder	boranko / directory	application/vnd.nativemind.boranko+json (its data.json)	<name>_boranko/	schemas/boranko/1.1/boranko.schema.json
.boranko 1.1 packed for transport	boranko / zip	application/vnd.nativemind.boranko+zip	.zip / .boranko.zip	same
.boranko 1.0 single file	boranko / single-json	application/vnd.nativemind.boranko+json	.boranko	schemas/boranko/1.0/boranko.schema.json
.comics (Comics.Editor)	comics / data	application/vnd.nativemind.comics+zip	.comics	schemas/comics/1.0/comics-data.schema.json
.comics legacy (images only)	comics / legacy	application/vnd.nativemind.comics+zip	.comics	schemas/comics/1.0/comics-metadata.schema.json
FDMESH warp sidecar	(not sniffed; .dome entry)	application/vnd.nativemind.freedome.fdmesh	.mesh	formats/fdmesh.ksy

Sniffing order — one function in every codec

Content wins; the extension is never consulted. Reference: tools/sniff/formats.mjs (sniff); corpus: conformance/sniff/cases.yaml.

1. Directory: dome.json with "format": "dome" → dome/directory; else data.json whose root has a pages array → boranko/directory; else unsupported-format.
2. ZIP (50 4B 03 04; the container is opened with the .dome ZIP rules — entry-name guard, limits; a broken container fails with its problem, e.g. validation-failed pointer /entries/<i> for ../x): first entry mimetype = the .dome MIME → dome/zip; root dome.json with "format": "dome" → dome/zip + warning no-mimetype; root data.json with layers or sounds (or a data.json that does not parse — the decoder then fails with validation-failed) → comics/data; root data.json with pages, or <x>_boranko/data.json → boranko/zip; only images (+ metadata.json / info.json) → comics/legacy; else unsupported-format.
3. ZELIM at offset 0: a complete 64-byte header with bytes 5..7 = 0 → zelim/binary; otherwise (e.g. the 9-byte Sphere placeholders) unsupported-format.
4. Text: after an optional UTF-8 BOM and JSON whitespace (space, tab, CR, LF) the first byte is { and the document is UTF-8 JSON: header.format == "zelim" → zelim/json; a pages array and version absent or 1.0.x → boranko/single-json; anything else → unsupported-format.
5. Everything else → unsupported-format (415).

A .zelim that matches neither variant (JSON without header.format: zelim, PNG, .dome content …) is unsupported-format for a .zelim reader.