feat(#537): wire the extended progression write path into the async daemon

[jeremydmiller]

Closes #537. Companion Marten filing: JasperFx/marten#4981; surfaced by JasperFx/CritterWatch#750.

What

Extended progression tracking (ExtendedProgressionEnabled) created the schema columns (heartbeat, agent_status, pause_reason, running_on_node) and a faithful read surface, but no daemon path ever persisted them — "built and never connected" (#519). This PR adds the daemon-level write path, flowing through the store abstraction so Marten and Polecat implement only the store-side write.

Design

• IEventDatabase.WriteExtendedProgressionAsync(ShardState, CancellationToken) — the store-side persistence hook, default-implemented as a graceful no-op (the established pattern), so every existing store compiles and degrades silently until it implements the write. The documented contract forbids touching progression (last_seq_id-equivalents) from this path, so a telemetry write can never race a concurrent batch commit into losing or regressing progress.
• IEventStore.ExtendedProgressionEnabled (default false) — store-level gate, read live per publication so a runtime flip (e.g. CritterWatch's forced enable of the DI-registered IEventStoreInstrumentation) is honored.
• ExtendedProgressionWriter — a ShardStateTracker observer subscribed by JasperFxAsyncDaemon at construction (the same shape as StoreUriStampingObserver / SkippedEventsCountObserver):
  • Agent status transitions (Started / Paused + pause_reason / Stopped) write immediately — a paused or stalled shard is exactly when persisted status matters most (the CritterWatch node-down / HWM-frozen alerting case).
  • Heartbeat ticks (the agents' existing ~10s timer) and per-batch-commit publications are throttled to one write per 5s per shard, so the heartbeat column advances on every tick without turning every batch commit into an extra progression-table write. The heartbeat write path is deliberately not coupled to progress advance.
  • Writes are serialized on a background block and strictly best-effort: a throwing store write is logged at debug and never fails or stalls the shard; a slow database never backs up the tracker's publication loop.
  • Carries AssignedNodeNumber through to running_on_node when a distribution layer stamped it.

Test evidence

New EventTests.Daemon.ExtendedProgressionWriterTests (9 tests): transitions write through; heartbeats throttle per shard (FakeTimeProvider); zero writes when the store hasn't opted in; HighWaterMark/AllProjections and telemetry-less publications skipped; a throwing database write is swallowed and subsequent writes continue; node-number carry; and an end-to-end pass through a real ShardStateTracker + SubscriptionAgent (start → Running write with heartbeat, stop → Stopped write).

Full local runs green: EventTests 562/562, EventStoreTests 72/72, CoreTests 470/470.

Clean-room end-to-end (with the companion Marten branch implementing the store write): the preserved #537 repro (plain AddMarten().AddAsyncDaemon(Solo), one async projection, flag forced via the DI IEventStoreInstrumentation) on locally-packed JasperFx.Events 2.31.0-dev.1 + Marten 9.17.0-dev.1:

--- running, t+15s ---  Counters:All  seq=47   heartbeat=4:50:40 PM  agent_status=Running  pause_reason=NULL
--- running, t+30s ---  Counters:All  seq=97   heartbeat=4:50:55 PM  agent_status=Running  pause_reason=NULL
--- running, t+45s ---  Counters:All  seq=146  heartbeat=4:51:10 PM  agent_status=Running  pause_reason=NULL
=== stopping host ===
--- after host stop --- Counters:All  seq=146  heartbeat=4:51:15 PM  agent_status=Stopped

Previously (2.29.0/2.30.1/2.30.2 × Marten 9.16.x): every one of those columns NULL at all times.

Store-side follow-ups

• Marten (required for end-to-end): MartenDatabase.WriteExtendedProgressionAsync as an UPDATE-only decoration of mt_event_progression + the IEventStore.ExtendedProgressionEnabled override — companion PR on JasperFx/marten referencing #4981.
• Polecat: inherits the graceful no-op until it implements the write (polecat#323 remains the tracker; its heartbeat-on-progress-advance path is unaffected).

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