@spec binding(t()) :: {:ok, map()} | {:error, atom()}

Return the explicitly versioned portable identity of a trusted definition.

This is not an executable continuation frame. It contains no functions, agent structs, model state, credentials, dependency objects or tracing context. Host references themselves must be nonsecret. A mutated definition is revalidated.

@spec new(keyword()) :: {:ok, t()} | {:error, atom()}

Validate a sequence definition without executing user code.

Required keyword options: :id, :version (nonempty UTF-8 strings, at most 512 bytes each), and :steps (1..255 atom-keyed maps with unique IDs). Optional kind: :sequence and failure_policy: :fail_fast are the only supported choices. Unknown or duplicate options are rejected.

Each step requires :id, an ExAgent struct in :agent, versioned references :definition, :policy, :model_ref, :output_ref, and :model_codec with dump/1 and load/2 functions. References use the existing %{id: ..., version: ...} convention (string keys also accepted). A mapping requires both :input (a pure arity-2 function) and :input_version (a version string). It will receive the initial input and confirmed outputs by step ID when execution is integrated. Without mapping, the first input is initial input and successors use prior output.

The complete encoded identity binding, including fingerprint, is limited to 65,536 JSON bytes. This is a definition limit, not a runtime journal reservation.

Resume a ready durable sequence from its exact public continuation reference.

Administrative recovery is explicit (ExAgent.Continuation.recover/3); this function never recovers an expired claim or refreshes a reference. Confirmed completed steps are data only. Options match run/3.

Execute a sequence using a required :continuation Writer configuration.

Optional :root_options restrict the shared scope; :step_options maps step IDs to ordinary run options. :observability and :trace_context are ephemeral. Returns a portable confirmed result, or a RunError with the confirmed partial. A failed checkpoint retains its retry token; retrying it never executes a step.

@spec validate_binding(t(), term()) :: :ok | {:error, atom()}

Validate stored identity against a freshly supplied trusted definition, without IO.

Malformed/future bindings reject as :invalid_composition_binding; well-formed changed identities reject as :composition_definition_changed. Never load host definitions or resolve modules from the stored binding. This check alone is not runtime admission, approval, or validation of a continuation's journal/ledger.