0567 — Stop line as session summary

Context

[0562] fixed the stopped line as bound identity and nothing else, so a session ends without numbers — “it was flaky” has no evidence. Nothing in-process holds instrument state: the whole metrics pipeline is DB truth polled by the collector onto __system.metrics, and a single instance’s session contribution is unrecoverable from any query. OBS renders its outputs’ internal counters at stop; the OTel SDK is the accumulate-and-export template (in-process cumulative instruments, a periodic reader, a final in-memory collect at shutdown).

Decision

• The stopped line becomes the session summary: bound identity, session duration, and the instance’s lifetime counters — every counter printed even at zero, <verb>_count registry keys. Emitted on EVERY exit including fatal-error teardown (the error is still returned, never logged; the line reports the transition and the numbers). The line reads memory only, never the database — metrics never hold up a shutdown, and error teardown often means the database is unreachable.
• The counters are metrics machinery, not a log-side struct: atomic counter fields plus a Snapshot() read-model on the instance-side metrics producer (pkg/metrics/producer), the object already threaded into the message/exception consumer provisioners and already running in the instance’s errgroup — zero new threading; it outgrows its abandoned-events name at build. Bumps happen at the worker layer from facts in hand (the outcomes slice after Commit returns nil, the reclaim fact off ClaimedRangeData), never inside datastores.
• Transport splits by shape: counter bumps are in-memory only; a flush tick in the producer’s Run loop produces current totals as KindCounter Measurements — the Kind declared for running totals, first used here; otelvulkan already maps KindCounter to a monotonic observable. Event-shaped metrics keep their per-event produce.
• Instance-emitted measurements carry instance identity as a series attribute: a session uuid minted per Consume call for the session counters (one session spans several worker rows); worker-scoped metrics may carry their worker_instance id. Dead sessions’ series freeze and age out with topic retention.
• Counter set, exact names settled against the row statuses at build: claimed, success, superseded, ready, deferred, dead, reclaimed, quarantined, abandoned, lease_lost. The CONVENTIONS start-line amendment lands with the build.
• The producer’s produced counter alone waits on presence (13d): no producer lifecycle by prior decision, so its stopped line is the presence heartbeat goroutine’s stop.

Consequences

Every teardown ends with evidence, including database-down ones, and Prometheus gains per-instance counters with no otelvulkan change. Rejected: querying the topic at exit (a round trip for data the process already holds, and a DB dependency at teardown); per-bump produce (doubles the write load of every consumed message); counting in the log pipeline (Debug narration is level-filtered); a counters home in consumergroup vocabulary (pure read-models only).