oaknut-filesystem 12.5.3

The pluggable filesystem contract for the oaknut family: detection, capabilities, geometry, partitions, and the identification coordinator.

oaknut-filesystem

The pluggable filesystem contract for the oaknut family — the base every Acorn (and, in principle, foreign) filesystem plugs into.

A filesystem is the unit of extension: Acorn DFS, Watford DFS, Opus DDOS, ADFS, AFS, … are peers, registered on the oaknut.filesystem entry-point axis (built on oaknut-extension). Each one:

• probes an image region and proposes what it is — with a confidence, evidence, and a candidate geometry;
• opens a region into a mount exposing a small core (list / stat / read / write / exists, and parsing its own path syntax) plus opt-in capability protocols (HierarchicalDirectories, AcornMetadata, BootOption, UserDatabase, RegionHost);
• declares its geometry grammar — the physical layouts it supports.

Two concerns are kept strictly apart:

• Geometry — the physical mapping of image bytes to logical sectors (track count, sides, interleave, density, CHS). This is the discimage DiscFormat layer, beneath the filesystem.
• Filesystem — the logical structure that turns sectors into files and directories.

This package also hosts the identification coordinator (identify()): it runs the registered filesystems over an image, ranks the candidates, and recurses into reserved regions (an ADFS host's tail, where an AFS or other filesystem may live) to produce a per-partition Identification tree.

It depends on no concrete filesystem package and imports none: filesystems are discovered purely through entry points, so any subset can be installed and the rest simply aren't handled.

See docs/dev/filesystem-extensions.md (architecture) and docs/dev/filesystem-extensions-plan.md (implementation plan).