Extends #927 (which zero-inited telemetry_events_dropped) to every counter
whose label domain is bounded and known at startup, so metrics are present in
Prometheus before their first event — a missing series then signals a broken
scrape rather than "nothing happened yet".
- add initialize_bounded_metrics(instance_type) on PrometheusMetrics; call it
per-process from main.py (api) and deriver/__main__.py (deriver).
- extract a shared _touch() helper; refactor initialize_telemetry_dropped_metrics
onto it (that one stays per-emitter in start() — it's prefix-dependent).
- explicit ALL_EVENT_TYPES / HIGH_VOLUME_EVENT_TYPES registry in telemetry.events,
drift-guarded by tests that walk BaseEvent subclasses.
- only VALID (task_type, token_type, component) tuples for deriver_tokens (the
cartesian product would fabricate impossible always-0 series); only high-volume
event types for sampled_out; high-cardinality labels (endpoint, workspace_name)
left open.
- gauges: zero-init embed_now_tasks_in_flight + telemetry_buffer_size; add a new
message_embeddings_pending backlog gauge, set each reconciliation cycle and
zero-inited at deriver startup (Rajat's pending/in-flight ask).
- backfills the tests #927 shipped without.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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