Module codes 

Status codes — one table shared verbatim by the FFI return values and the pipe frame header (docs/ARCHITECTURE.md error code table).

Append only; renumbering is a breaking protocol change. Downstream, fmf-ffi’s contract_tests pin these against literals as an independent tripwire for accidental edits of this file.

Constants

INVALID_ARG

A caller-supplied argument was invalid (null/length contract violated, or a version mismatch on the pipe Hello handshake).

IO

An I/O error occurred (index file or volume read/write).

LOCKED

The index dir’s writer lock is held by another process (single-writer invariant, cross-process).

NOT_ADMIN

The operation needs administrator rights (MFT/USN access) that the caller lacks.

OK

Success.

PANIC

An internal panic was caught at the FFI/pipe boundary (catch_unwind); detail is available via fmf_last_error.

QUERY_SYNTAX

The query string failed to parse.

STALE

Structural generation moved (or a result handle was evicted) — the client re-runs the query.

VOLUME

A volume could not be opened or read (unsupported filesystem, missing, or otherwise unavailable).