Copy execution transparency (Fáza 3)

Per-copy execution facts — latencia, realizovaný slippage, fill vs zlyhanie — zachytené pri každom pokuse o kopírovanie, surfacované ako per-profile transparency report. Vypnuté predvolene; povolte s App:Copy:TransparencyEnabled=true. Keď vypnuté, copy engine bajt-po-bajte nezmenený: host emituje do no-op sink, nič napísané.

Ako to funguje

CopyEngineHost ──Record(fact)──▶ ICopyEventSink
                                   │
             (transparency off) NullCopyEventSink   → zahadzuje (predvolené; nulové hot-path náklady)
             (transparency on)  ChannelCopyEventSink → bounded in-memory channel (DropOldest)
                                   │
                                   ▼
                          CopyExecutionDrainer (BackgroundService)
                                   │  batchuje každý App drain interval
                                   ▼
                          CopyExecution append-only table  ◀── GET /api/copy/profiles/{id}/transparency

• Hot path zostáva bez I/O. Host volá ICopyEventSink.Record(...) — non-blocking, nikdy-nehodí enqueue. Nikdy nečaká, nikdy sa nedotýka DB, nikdy neblokuje order execution.
• Strata preferovaná pred back-pressure. Channel bounded (CopyExecutionChannelCapacity) s DropOldest: ak DB drainer stojí, najstaršie transparency riadky dropnuté namiesto oneskorenia copy. Transparency = best-effort telemetria, nie trading dependency.
• Out-of-band perzistencia. CopyExecutionDrainer drainuje channel v batchoch (CopyExecutionDrainBatchSize) na CopyExecutionDrainInterval, píše CopyExecution riadky cez scoped DataContext. Finálny flush pri shutdown.
• Fakty, nie príkazy. CopyExecution = append-only log (ako InstanceLog/AuditLog), nie aggregate. Read model sa pýta priamo (CQRS-lite), aggregates in-memory.

Čo sa zaznamenáva

Jeden CopyExecutionRecord na pokus o kopírovanie na jednej destinácii:

Kind	Kedy	Nesie
Opened	copy order umiestnená	symbol, side, wire volume, master price, realizovaný slippage (points), latencia (ms)
Failed	copy open hodila/odmietnutá	symbol, side, master volume/price, latencia, dôvod zlyhania (exception type)

(Closed/Skipped/Reconciled existujú v enum pre budúcu expanziu.)

Report

GET /api/copy/profiles/{id}/transparency (owner-scoped) vráti, za najnovších 500 faktov:

• Summary — total, opened, failed, fill rate, priemerná latencia (ms), priemerný slippage (points).
• Recent — raw recent facts (destination, source position, symbol, side, volume, master price, slippage, latencia, dôvod, timestamp).

Konfigurácia (App:Copy)

Nastavenie	Predvolené	Efekt
TransparencyEnabled	false	Zapne per-copy fact capture + drainer pre node.

Channel capacity, drain batch size, drain interval = CopyDefaults konštanty (CopyExecutionChannelCapacity / CopyExecutionDrainBatchSize / CopyExecutionDrainInterval).

Testy

• Jednotka (CopyTransparencyTests) — úspešný open emituje Opened fact so správnym symbol/side/volume/latencia; odmietnutý open emituje Failed fact s dôvodom. Cez capturing sink.
• Integrácia (CopyExecutionDrainerTests, reálny Postgres) — drainer perzistuje buffered facts do CopyExecution log; prázdny sink nič nepíše.
• DST — host fire-and-forget s no-op default sink, takže deterministic copy stress suite zostáva zelená (23/23).