Enum ExecMode 

pub enum ExecMode {
    Dev,
    Prod,
}

The dev/prod execution mode (NS-A4, docs/stdlib-spec.md §4b, ruled 2026-07-18): the knob that decides WHERE execution stops on an unordered comparand — never WHAT values are fabricated.

The split is fenced to placement: it exists only where the prod behavior is defined, total, and fabricates no data. Ordering contexts qualify (sort/sorted/min/max; A7 adds heap_push): every element is preserved, the order is deterministic, saves/replay are safe. Fabrication never qualifies — int("potato"), OOB indexing stay always-fault in both modes. Effect rows are mode-independent (the checker doesn’t know modes exist).

• Dev (the default — the Rust dev-profile analogy, like debug-build overflow checks): a float NaN comparand in an ordering context is a turn-terminating RuntimeError::UnorderedComparand fault, surfacing the upstream bug at its first ordering consumption.
• Prod: the pinned non-fabricating total order applies — ordinary IEEE order with -0 == +0 as a tie, NaN greater than everything, NaN-vs-NaN ties (deliberately NOT IEEE totalOrder, whose -0 < +0 would split ordering from == on clean data). Execution keeps moving.

On NaN-free data the modes agree exactly and cohere with </==.

The knob’s home is project config (brink.toml profile) with a host-API override (ruled 2026-07-19; tooling wires the config side). This runtime mechanism is the host-API leg: set it via [Story::set_exec_mode] / [FlowInstance::set_exec_mode]. The mode is a host/build knob, not story state — it is never embedded in .inkb (mirroring dialect/types) and never persisted in saves.

Variants

Dev

Fault on unordered comparands (NaN) in ordering contexts.

Prod

Keep moving: place NaN by the pinned non-fabricating total order.

Trait Implementations

impl Clone for ExecMode

fn clone(&self) -> ExecMode

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for ExecMode

impl Debug for ExecMode

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

Formats the value using the given formatter.

impl Default for ExecMode

fn default() -> ExecMode

Returns the “default value” for a type.

impl Eq for ExecMode

impl PartialEq for ExecMode

fn eq(&self, other: &ExecMode) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for ExecMode