Task: The feed seam: common producer interface + per-kind factory

The seam the original FX PoC architecture doc specified (design question 8, feed manager) finally exists: one common feed interface every producer implements, and a factory mapping asset class to producer builder. FX and IR curve producers are both behind it; every control-plane piece (folder cascade, per-config handler, controller, auto-start, ingest) dispatches through it.

• A common feed interface exists (generalizing IFxSpotFeed) exposing the shape both producers already have: source_name, qualifier, role, start, stop, and a conflict key for qualifier+role semantics.
• fx_spot_feed and ir_curve_feed both implement it; ir_curve_feed gains the interface it currently lacks.
• A factory maps asset class to producer builder; both kinds are constructible through it. The factory is the registration point for future asset classes.
• The factory lives where the doc specified: ores.marketdata.api hosts the interface; ores.synthetic.api registers the producers.

The seam is built in one pass over the producers, then wired through the factory:

1. Interface: IFeed replaces IFxSpotFeed in ores.marketdata.api (include/ores.marketdata.api/domain/i_feed.hpp). It exposes the shape both producers already have — source_name(), qualifier(), role(), start(), stop(), publish_count() — plus a conflict_key() that joins (qualifier, role) with a unit separator (the IR qualifier+role conflict semantics, expressed by the feed itself). start() drops the on_tick handler: the only caller passes a no-op, and both feeds publish to NATS themselves. ore_key() stays a concrete accessor on fx_spot_feed (FX-specific, no IR analog).

2. Producers move into ores.synthetic.api (include/ores.synthetic.api/feeds/

   • src/feeds/, namespace ores::synthetic::feed, ORES_SYNTHETIC_API_EXPORT):

   fx_spot_feed, ir_curve_feed, ir_curve_template_resolver, and the make_*_feed builders. fx_spot_feed gains a source_name constructor parameter and derives its qualifier from its ore_key via split_market_series_key at construction; ir_curve_feed gains : public IFeed and conflict_key(). synthetic_producer_subject moves with the FX producer so the factory builds subjects the same way the controller does.

3. Factory: feed_factory in the api maps a kind string to a producer builder (feed_build_context with the nats client pair + caller bearer token, and per-kind build inputs in a variant). make_default_feed_factory() registers both kinds — the registration point for future asset classes. make_fx_spot_feed builds from the persisted fx_spot_generation_config + gmm_component rows (mirroring the auto-start path; the FX vintage resolution stays in feed_controller::start until the client-supplied-params path is deleted by the control-plane task).
4. Service wiring: both auto-start walks dispatch through the factory. The FX controller gains add() (mirroring curve_feed_controller::add); both controllers accept IFeed. The ad-hoc start() path keeps its inline construction until the per-config control-plane task deletes it.
5. The api CMakeLists gains the producer deps (nats, marketdata.api, marketdata.client/core, database, refdata.core); component_files.cmake is regenerated; a factory test in the api tests covers both kinds, kind enumeration, and wrong-input rejection.

Manual QA scenarios (scaffolded via compass add test_scenario, run through the QA Validation Runner panel) that verify this task. Link new ones here as they're created; the scenario doc itself links back via its "Verifies task" field.

The seam is built and wired end to end:

• IFeed replaces IFxSpotFeed in ores.marketdata.api (domain/i_feed.hpp): source_name(), qualifier(), role(), conflict_key(), start(), stop(), publish_count(). start() takes no handler; both producers publish to NATS themselves. ore_key() remains a concrete accessor on fx_spot_feed.
• Both producers implement it. fx_spot_feed, ir_curve_feed and ir_curve_template_resolver moved to ores.synthetic.api (feeds/, namespace ores::synthetic::feed, ORES_SYNTHETIC_API_EXPORT); synthetic_producer_subject moved with the FX producer. make_fx_spot_feed builds an FX feed from its persisted config plus gmm_component rows (the factory path leaves the FX vintage lookup in feed_controller::start until the control-plane task deletes it); make_ir_curve_feed builds the IR feed, vintage resolution included.
• feed_factory maps a kind string to a producer builder: feed_build_context (nats client pair + caller bearer token) and per-kind build inputs in a variant; make_default_feed_factory() registers fx_spot and ir_curve — the registration point for future asset classes.
• Service wiring: both auto-start walks dispatch through the factory; both controllers accept IFeed; feed_controller::add() downcasts internally for status logging.
• The api CMakeLists gained the producer deps; component_files.cmake regenerated; feed_factory_tests.cpp covers both kinds, kind enumeration, unknown-kind and wrong-input rejection, and replacement registration.

Acceptance: the interface exists and generalizes IFxSpotFeed; both producers implement it (ir_curve_feed gained the interface it lacked); the factory constructs both kinds; the interface lives in ores.marketdata.api and the producers register in ores.synthetic.api. All met.

Verification: full build green; compass build rat green (60 suites); the new factory test 6/6 passing; the synthetic service restarted on the new build.