1.0.0

First stable release. Hardens the runtime under contention and at high cardinality, brings the OTLP path up to spec, fixes deadlock and leak risks in the export pipeline, and lands a full audit of the documentation against the actual public API.

Added

• OTEL_METRIC_CARDINALITY_LIMIT (default 2000) caps distinct label sets per vector metric. Excess label sets aggregate into one shared series tagged otel.metric.overflow=true. Dropped count exposed via instrument_registry:cardinality_dropped/1.
• instrument_otlp_retry module: bounded exponential backoff with Retry-After honoured, classifying transport and HTTP errors per the OTel spec. Configurable via OTEL_EXPORTER_OTLP_MAX_RETRIES, OTEL_EXPORTER_OTLP_RETRY_INITIAL_DELAY_MS, OTEL_EXPORTER_OTLP_RETRY_MAX_DELAY_MS.
• Span attribute value length limit (OTEL_ATTRIBUTE_VALUE_LENGTH_LIMIT), per-event and per-link attribute count limits (OTEL_EVENT_ATTRIBUTE_COUNT_LIMIT, OTEL_LINK_ATTRIBUTE_COUNT_LIMIT); excess attributes counted in dropped_attributes_count and emitted as droppedAttributesCount in OTLP.
• Tracestate caps at 32 entries / 256 bytes; baggage caps at 180 entries / 8192 bytes per W3C trace-context.
• instrument_attributes:apply_limits/2,3 and truncate_value/2 helpers.
• Span Export Path section in the design and internals guide explaining the full chain from end_span to OTLP, with explicit notes that instrument_tracer_nif serves the flight recorder only.
• Test coverage for 28 documented public APIs that previously had no call sites in CT (propagation inject_headers/extract_headers/call_with_context/cast_with_context, context remove_value/spawn_link_with_context, config set_verbose_tracing/is_verbose_tracing/enable_exporter/disable_exporter, tracer record_exception/update_name, instrument_test:assert_log_trace_context, logger add_trace_context/emit, metric remove_label/clear_labels/set_gauge_to_current_time, exporter callback contracts).

Changed

• Batch processor force_flush/0 and the max-batch-size trigger no longer block the gen_server loop. An export worker is spawned and completion arrives as {export_done, ...}; concurrent flush callers are batched and replied to via gen_server:reply/2. A kill timer enforces export_timeout_millis without blocking the loop.
• instrument_exporter shutdown now casts the hook unregister so the reply path stays unblocked.
• instrument_span_processor:on_start/2 now has a 5 s safety timeout; the tracer hot path uses the inline persistent_term form.
• OTLP exporters return {error, retryable, _} vs {error, permanent, _}. The batch processor keeps retryable batches for up to max_batch_retries cycles and drops permanent errors.
• Probability sampler hashes the upper 8 bytes of the trace id, matching the Java/Go/Python reference SDKs.
• Status transitions now follow the OTel spec: unset -> ok|error, error -> ok (success overrides), error -> error updates the description, ok is final.
• Batch processor clamps max_export_batch_size to max_queue_size on init with a warning.
• Documentation snippets fixed across guides/, book/, and README.md: 6 syntax bugs, 8+ calls to non-existent or wrong-arity functions, wrong arg shapes for set_sampler, parent_based config, metric_view record literal, exporter_otlp:export, and stale config keys (schedule_delay_millis, export_timeout_millis).
• Book chapter prose smoothed for readability.

Fixed

• Histogram exemplar reservoirs are now freed on unregister.
• Registry unregister no longer scans the global persistent_term index; iterates the metric's own labels_map instead.
• Baggage set/remove/clear use set_current/1 so process-dictionary context tokens no longer accumulate.
• instrument_exporter_console:export/2 and instrument_metrics_exporter_console:exporter_export/2 no longer crash when configured with output => {file, Path}. The {file, Fd} wrapper used by shutdown/1 is now unwrapped before io:put_chars/2.

Removed

• instrument_exporter_kafka documentation section: the module never existed in src/exporters/.