feat(discovery): build_similarity_sources + worker sweep/trigger wiring

Adds registry.build_similarity_sources() (always constructs
ListenBrainzSource; reachability is a per-run health() concern, not a
startup gate) and wires discovery into the worker's main loop: a
scheduled sweep gated on discover.enabled + DISCOVER_TICK_SECONDS, and
a one-shot discover.requested trigger mirroring the existing
scan.requested pattern.

Also hardens run_discovery's health-check pass: a source whose
health() raises is now logged and skipped instead of aborting the
whole sweep (accepted finding from the Task-3 review).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

worker/lyra_worker/main.py

@@ -3,14 +3,19 @@ import time
 from lyra_worker.claim import claim_next
 from lyra_worker.config import get_config
 from lyra_worker.db import wait_for_db
+from lyra_worker.discovery import DiscoveryConfig, run_discovery
 from lyra_worker.library import clear_staging_root
 from lyra_worker.monitor import MonitorConfig, reconcile, sweep
 from lyra_worker.pipeline import run_pipeline
-from lyra_worker.registry import build_adapters, build_browser, build_probe, build_resolver, build_tagger
+from lyra_worker.registry import (
+    build_adapters, build_browser, build_probe, build_resolver,
+    build_similarity_sources, build_tagger,
+)
 from lyra_worker.scan import scan_library
 
 IDLE_SLEEP = 2.0
 MONITOR_TICK_SECONDS = 60.0
+DISCOVER_TICK_SECONDS = 300.0  # check the discovery interval every 5 min (interval itself is hours)
 DEST_ROOT = "/music"  # must match run_pipeline's default library root
 _TRUE = {"1", "true", "yes", "on"}
 
@@ -32,6 +37,14 @@ def _run_scan(conn, resolver, probe, browser, dest_root: str = DEST_ROOT) -> Non
     print(f"worker: library scan done — {result.imported} imported, {result.skipped} skipped", flush=True)
 
 
+def _run_discovery(conn, sources, browser, config=None) -> None:
+    cfg = DiscoveryConfig.from_config(config if config is not None else get_config(conn))
+    result = run_discovery(conn, sources, browser, cfg)
+    _set_config(conn, "discover.result", f"artists {result.artists}, albums {result.albums}")
+    _set_config(conn, "discover.requested", "false")
+    print(f"worker: discovery done — {result.artists} artists, {result.albums} albums", flush=True)
+
+
 def run_forever() -> None:
     conn = wait_for_db()
     clear_staging_root(DEST_ROOT)  # sweep any staging dirs orphaned by a prior crash
@@ -40,9 +53,11 @@ def run_forever() -> None:
     tagger = build_tagger()
     browser = build_browser()
     probe = build_probe()
+    similarity_sources = build_similarity_sources(get_config(conn))
     print(f"worker: {len(adapters)} adapter(s) enabled: {[a.name for a in adapters]}", flush=True)
     print("worker: waiting for jobs", flush=True)
     last_tick = 0.0
+    last_discover_tick = 0.0
     try:
         while True:
             config = get_config(conn)
@@ -56,6 +71,15 @@ def run_forever() -> None:
                     conn.rollback()
                 last_tick = now
 
+            dcfg = DiscoveryConfig.from_config(config)
+            if dcfg.enabled and now - last_discover_tick >= DISCOVER_TICK_SECONDS:
+                try:
+                    _run_discovery(conn, similarity_sources, browser, config)
+                except Exception as e:  # a discovery error must never kill the worker
+                    print(f"worker: discovery sweep failed: {e}", flush=True)
+                    conn.rollback()
+                last_discover_tick = now
+
             if str(config.get("scan.requested", "")).strip().lower() in _TRUE:
                 try:
                     _run_scan(conn, resolver, probe, browser)
@@ -64,6 +88,14 @@ def run_forever() -> None:
                     conn.rollback()
                     _set_config(conn, "scan.requested", "false")
 
+            if str(config.get("discover.requested", "")).strip().lower() in _TRUE:
+                try:
+                    _run_discovery(conn, similarity_sources, browser, config)
+                except Exception as e:  # a discovery error must never kill the worker
+                    print(f"worker: discovery run failed: {e}", flush=True)
+                    conn.rollback()
+                    _set_config(conn, "discover.requested", "false")
+
             job_id = claim_next(conn)
             if job_id is None:
                 time.sleep(IDLE_SLEEP)