/**
 * Step overrides (spec §13.2/§13.3): replace any step, by name, with a stub — including one nested
 * inside a branch arm, loop/foreach body, parallel arm, or nested workflow. An override naming a step
 * the workflow does not contain fails immediately, at construction, rather than surfacing later as a
 * confusing mid-run failure or (worse) silently doing nothing.
 *
 * Implementation: an override is spliced into the node tree as an ordinary FUNCTION step, preserving the
 * REAL step's name/description/inputSchema/outputSchema/retry/maxDurationMs. Two things fall out of that
 * for free, with no engine changes at all:
 *  - the stub's return value is validated against the real step's declared `outputSchema`, by the SAME
 *    function-step validation every workflow already goes through (step-runner.ts) — a stub that has
 *    drifted from the contract it stands in for fails the test, not a silent divergence;
 *  - a stub that throws drives the real step's retry/crash/resume machinery (spec §13.3), because it now
 *    IS a function step under that policy — the otherwise-unreachable failure path becomes reachable
 *    without hand-rolling code that fails on purpose.
 *
 * `src/testing` stays a pure consumer of `src/flow` — no engine internals are touched, keeping the
 * override mechanism entirely a testing-layer concern (spec §13.1).
 */
import type { StepRunArgs, WorkflowDefinition } from "../flow/types.ts";
/** A step stub (spec §13.2): same shape as a function step's `run`, so a thrown error drives retry/crash/resume. */
export type StepOverride = (args: StepRunArgs<unknown>) => unknown | Promise<unknown>;
/** Per-step stubs, keyed by step name — any step, of any kind, anywhere in the tree. */
export type StepOverrides = Readonly<Record<string, StepOverride>>;
/**
 * Splice `overrides` into `workflow`'s node tree, returning a new `WorkflowDefinition`. Returns
 * `workflow` unchanged when there is nothing to override. Throws immediately when an override names a
 * step the workflow does not contain (spec §13.3).
 */
export declare function applyStepOverrides(workflow: WorkflowDefinition, overrides: StepOverrides | undefined): WorkflowDefinition;
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