OpenTelemetry instrumentation for the Statifier family of statechart packages.

Attaches to the public :telemetry events the family emits - starting with statifier's [:statifier, :session, ...] contract (Statifier.Session.Telemetry) - and turns them into OpenTelemetry spans, span events, and span links. The library depends only on opentelemetry_api; hosts bring their own SDK and exporter.

setup/0/setup/1 attach OpentelemetryStatifier.Handler.handle_event/4 to every name Statifier.Session.Telemetry.events/0 returns, one :telemetry.attach/4 call per name under a per-event handler id, so a raise in one event's handling never costs the others (deps/telemetry/src/telemetry.erl:109-116). teardown/0 detaches all of them.

A macrostep :start opens a root span named statifier.macrostep, and the :stop whose span_ref matches closes it, carrying statifier.session_id, statifier.trigger, statifier.outcome, the macrostep's counters, and its resulting statifier.configuration as attributes (OpentelemetryStatifier.Handler, OpentelemetryStatifier.SpanTable). Span start times come from each event's own monotonic_time, so a macrostep span's wall time tracks the statifier.duration measurement closely - with one documented exception. Statifier emits the :initialize macrostep's :start from the session's init/1 and its :stop from the following handle_continue, so that span opens after some of the work it covers, and reads materially shorter than statifier.duration reports. The skew is accepted rather than corrected; see the README and docs/adr/0003-handler-attach-and-span-table-mechanism.md.

Everything that fires between a :start and its :stop - the eleven [:statifier, :session, :effect, _] events, the nine [:statifier, :session, :trace, _] events, :interpret, :unroutable, and :halt - lands as a span event on the session's open macrostep span, attributes mapped uniformly by OpentelemetryStatifier.Attributes (locations flattened to statifier.source.line/.column, the raw effect struct never serialized, datamodel values excluded unless setup/1 received record_datamodel_values: true). Each macrostep span is the root of its own trace, stitched to its neighbors with span links: one to the same session's previous macrostep span, and - on a child session's :initialize macrostep - one to the invoking parent's macrostep span, resolved from the :init event's invoked_by. The bridge does not leak on crashes: :terminate removes the session's rows from the span table (ending a still-open macrostep span with an error status), and because :terminate does not fire on a brutal kill, OpentelemetryStatifier.SpanTable also sweeps on a timer, ending the orphaned spans of sessions whose process no longer exists the same way. With trace: false the core emits no trace-family events at all, so the bridge degrades to macrostep-grained spans with effect-level span events and needs no configuration of its own. The design this package implements lives in statifier-ex: docs/opentelemetry.md (span topology, context propagation, cardinality, failure tolerance) and st-ADR-0062 (packaging and scope).