# Internal: File Operations

`internal/fileops` owns the narrow mechanics for atomically visible replacement of one
byte file. Callers keep ownership of serialization, validation, cancellation,
and destination-directory policy.

## Destination Paths

Ordinary workspace replacement uses standard operating-system path semantics.
Callers with a root-scoped safety contract own that validation at their boundary.

Remote object acquisition uses a writer supplied by the storage owner. The
writer receives a `fileops`-owned, already-open sibling temporary file rather
than a mutable destination path. Callers still own remote object selection,
validation, conflict handling, and final mode.

Directory bundles are not promoted by `internal/fileops`; extraction owns its
validated Notarius bundle rename.

## Cleanup Contract

`RemoveAllUnderRoot` accepts an explicit root and a proper descendant, opens
that root with `os.OpenRoot`, and removes the normalized root-relative target
with `Root.RemoveAll`. It rejects root, traversal, and out-of-root targets; a
missing target is successful. `RemoveFileUnderRoot` additionally requires an
existing leaf to be regular. Command and post-publish policy remains owned by
`internal/app`.

## Bounded Reads

`ReadFileBounded` opens a normal path and reads at most its caller-supplied
limit. Credential mode policy and environment precedence remain owned by
`internal/app`.

## Replacement Contract

`ReplaceFileAtomic` requires an existing destination directory. It creates a
sibling temporary file, writes the complete byte sequence, applies the
caller-supplied mode, closes the file, runs an optional pre-rename check, and
replaces the destination with a rename.

The pre-rename check is the last point at which a caller can cancel without
installing a new destination. A failure before the rename leaves the old
destination unchanged and removes the temporary file. Successful replacement
provides atomic visibility; it makes no crash- or power-loss durability claim.

Replacement follows the operating system's same-filesystem rename semantics.
If a platform cannot replace an existing destination, the operation returns an
error and never removes the old file as an emulation step.

`WriteFileAtomic`, copy helpers, and downloaded temporary-file installation
retain their compatibility behavior of creating the destination parent with
the repository's workspace permissions before using this contract.