Format detection

openmassspec_io::detect_format(path) inspects the filesystem entry at path and returns a Detected { path, format } if and only if the signature of a supported vendor matches. The detection rules are:

Vendor	Path kind	Signature
Bruker	Directory	Contains analysis.tdf and analysis.tdf_bin.
Agilent	Directory	Contains AcqData/MSScan.bin.
Waters	Directory	Contains _HEADER.TXT.
Thermo	File	First 18 bytes match the Finnigan header (see below).
SCIEX	File	.wiff extension (case-insensitive) with a sibling <name>.wiff.scan file.
Shimadzu	File	.qgd or .lcd extension (case-insensitive) whose first 8 bytes are the CFBF/OLE2 signature.

For directories, the checks run in the order above (Bruker, then Agilent, then Waters) and stop at the first match. Bruker and Agilent bundles are both commonly named <run>.d/, so they are disambiguated by contents, not by the directory name - detection never inspects the extension for directory formats.

For files, the checks run Thermo, then SCIEX, then Shimadzu, and stop at the first match.

Thermo and Shimadzu detection are content-based, not purely extension-based. A .raw suffix is not sufficient (and not required) for Thermo: detect_format opens the file and checks whether bytes 2 through 17 equal the UTF-16LE string Finnigan, which is the Thermo Finnigan file signature. Shimadzu additionally requires the first 8 bytes to match the CFBF/OLE2 container signature - unlike SCIEX's .wiff, there is no sibling file to corroborate against, so the magic-byte check is the content-level signal used instead. Every other signature is a directory-entry or extension-only check, which keeps detection cheap even for stat-heavy filesystems.

Edge cases

• A directory that does not match any of the Bruker / Agilent / Waters content checks is returned as None, regardless of its name or extension. We do not heuristically descend looking for alternate bundle layouts.
• A symlink to a Thermo .raw file is treated as a regular file; the signature check reads through the link to the target's content.
• A .wiff file with no sibling .wiff.scan file is not detected as SCIEX - detect_format returns None even though the extension matches, because the reader needs the paired scan file.
• A .qgd or .lcd file whose first 8 bytes are not the CFBF/OLE2 signature is not detected as Shimadzu, even though the extension matches - this rejects garbage/renamed files the same way the SCIEX/Thermo checks do.
• Casing: the SCIEX .wiff and Shimadzu .qgd/.lcd extension matches are case-insensitive, but directory-bundle entry names are checked exactly as the vendor writes them (analysis.tdf, not Analysis.TDF; AcqData, not acqdata).

CLI behavior

vendor2mzml info /not/a/vendor/file.txt

exits with status 1 and prints error: ... does not look like a supported vendor format. There is no fallback to peeking file contents - if detection fails, the call fails.