Enum BackendError 

pub enum BackendError {
    MemWriter(MemWriterError),
    Sealed,
    Io(Error),
    Other(String),
    ParentMismatch {
        expected: String,
        actual: String,
    },
}

Errors surfaced by MemBackend.

The Sealed variant is the typed read-only signal — backends that physically cannot write (archive) return it from every mutating method. Callers (the engine’s mutation pipeline) branch on the discriminant before reaching the backend; a Sealed reaching this layer is a programming error in the upstream capability check.

Variants

MemWriter(MemWriterError)

Re-thrown from the existing MemWriterError surface so folder-backend implementations can lift MemWriter failures without lossy conversion.

Sealed

Backend physically rejects writes. Returned by the archive backend and any future read-only backend (e.g. registry pin).

Io(Error)

Filesystem IO failure outside the MemWriterError path.

Other(String)

Backend-specific failure not modelled by the variants above. Carries an agent-readable message; structured backend errors add their own variant.

ParentMismatch

Parent-ref pinning guard tripped on MemBackend::commit_with_expected_parent — the backend’s current head no longer matches the caller’s expected_parent. A sibling writer (another Engine instance, an out-of-band git pull, a manual git operation) advanced the on-disk state between the snapshot the caller pinned and now. The engine layer maps this into MEM_RELOADED / RENAME_PARTIAL_FAILURE depending on whether other mems already committed in the same logical operation. Today only the git-branch backend (planned override) produces this variant; folder and archive backends inherit the default impl of commit_with_expected_parent which delegates to commit without parent checking.

Fields

expected: String

actual: String

Trait Implementations

impl Debug for BackendError

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Display for BackendError

fn fmt(&self, __formatter: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Error for BackendError

fn source(&self) -> Option<&(dyn Error + 'static)>

Returns the lower-level source of this error, if any.

fn description(&self) -> &str

👎Deprecated since 1.42.0:

use the Display impl or to_string()

fn cause(&self) -> Option<&dyn Error>

👎Deprecated since 1.33.0:

replaced by Error::source, which can support downcasting

fn provide<'a>(&'a self, request: &mut Request<'a>)

🔬This is a nightly-only experimental API. (error_generic_member_access)

Provides type-based access to context intended for error reports.

impl From<BackendError> for EngineError

fn from(source: BackendError) -> Self

Converts to this type from the input type.

impl From<Error> for BackendError

fn from(source: Error) -> Self

Converts to this type from the input type.

impl From<MemWriterError> for BackendError

fn from(source: MemWriterError) -> Self

Converts to this type from the input type.