fleetd #562 follow-up: extract loopHealthSource factory, pin its wiring

PR #579's inline `new FleetMcp.LoopHealthSource(poller::health, ...)` in
Fleetd.main had nothing a test could call directly. Measured: replacing
poller::health with a constant () -> RUNNING compiled clean and left all
1771 tests green (see issue #562 comment "HOLD on PR #579").

Extracts the inline construction to a package-private Fleetd.loopHealthSource
factory, the same style as the sibling capacitySource/healthCoverageSource
factories, and adds FleetdLoopHealthSourceWiringTest with three separate
assertions: the statusPoller half, the sessionReaper half, and the
reaper == null branch (still STOPPED).

fleetd/src/main/java/dev/ltms/fleet/Fleetd.java

@@ -666,8 +666,7 @@ public final class Fleetd {
             return configured == null ? null : configured.effectiveCredentialId();
         }, outagePolicy);
 
-        FleetMcp.LoopHealthSource loopHealth = new FleetMcp.LoopHealthSource(poller::health,
-                () -> reaper == null ? LoopWatchdog.State.STOPPED : reaper.health());
+        FleetMcp.LoopHealthSource loopHealth = loopHealthSource(poller, reaper);
         FleetMcp mcp = new FleetMcp(messages, workers, sessions, identity, presence,
                 primaryRegistry, callers, FleetMcp.AuthorizationMode.ENFORCED, metrics,
                 capacitySource(config, cfg, profile -> liveCountRef.get().apply(profile)),
@@ -1042,6 +1041,31 @@ public final class Fleetd {
         });
     }
 
+    /**
+     * fleetd #562 follow-up: package-private factory for {@code fleet_list}'s and {@code
+     * /healthz}'s {@code loopHealth} source, extracted out of {@code main} for the same reason
+     * {@link #capacitySource} and {@link #healthCoverageSource} were. Before this ticket the
+     * {@link FleetMcp.LoopHealthSource} was built inline with a bare {@code new}, so there was
+     * nothing a test could call directly — measured: replacing {@code poller::health} with a
+     * constant {@code () -> LoopWatchdog.State.RUNNING} at the call site compiled clean and left
+     * the full suite green, meaning the daemon could report the {@link StatusPoller} as always
+     * {@code RUNNING} even while it was actually stalled. That is a false negative on the exact
+     * signal this ticket exists to surface, and is the mirror of a false positive muting a real
+     * monitoring component — worse, because there is no noise for anyone to notice and then
+     * silence. {@link FleetdLoopHealthSourceWiringTest} calls this factory directly and pins both
+     * halves separately, plus the {@code reaper == null} branch below.
+     *
+     * <p>{@code reaper} may be {@code null} — a {@link SessionReaper} is only constructed when
+     * {@code lifecycle.idleTtlSeconds} is configured (see the {@code reaper} local above) — and
+     * this factory preserves the existing behaviour of reporting {@link LoopWatchdog.State#STOPPED}
+     * in that case, rather than a {@code NullPointerException} on the first {@code fleet_list} or
+     * {@code /healthz} call.
+     */
+    static FleetMcp.LoopHealthSource loopHealthSource(StatusPoller poller, SessionReaper reaper) {
+        return new FleetMcp.LoopHealthSource(poller::health,
+                () -> reaper == null ? LoopWatchdog.State.STOPPED : reaper.health());
+    }
+
     /**
      * fleetd #248: package-private factory for the member worktree/branch lookup {@link
      * CompletionResolver} uses to name a fallback report's worktree and branch (fleetd#241).

fleetd/src/test/java/dev/ltms/fleet/FleetdLoopHealthSourceWiringTest.java

@@ -0,0 +1,174 @@
+package dev.ltms.fleet;
+
+import dev.ltms.fleet.herdr.AgentControl;
+import dev.ltms.fleet.herdr.FakeHerdr;
+import dev.ltms.fleet.inject.Injector;
+import dev.ltms.fleet.inject.LoopWatchdog;
+import dev.ltms.fleet.inject.StatusPoller;
+import dev.ltms.fleet.mcp.FleetMcp;
+import dev.ltms.fleet.peer.Capability;
+import dev.ltms.fleet.peer.PeerHandle;
+import dev.ltms.fleet.peer.PeerLauncher;
+import dev.ltms.fleet.peer.SpawnRequest;
+import dev.ltms.fleet.placement.PlacementDecision;
+import dev.ltms.fleet.session.SessionManager;
+import dev.ltms.fleet.session.SessionReaper;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+
+import java.util.List;
+import java.util.Set;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+/**
+ * fleetd #562 follow-up (issue comment "HOLD on PR #579"): {@code Fleetd.main}'s {@code loopHealth}
+ * local used to be a bare {@code new FleetMcp.LoopHealthSource(poller::health, ...)} built inline,
+ * with nothing a test could call directly. Measured on that shape: replacing {@code
+ * poller::health} with a constant {@code () -> LoopWatchdog.State.RUNNING} at the call site
+ * compiled with 0 errors and left all 1771 existing tests green — the daemon could be changed to
+ * always report the {@link StatusPoller} as {@code RUNNING}, so the watchdog could never fire and
+ * a stalled poller would be invisible, while every test stayed green. That is exactly the false
+ * negative this ticket exists to prevent.
+ *
+ * <p>The five tests PR #579 added ({@code FleetMcpTest}, {@code FleetAppTest}) all build their own
+ * {@link FleetMcp.LoopHealthSource} directly with fixed lambdas — they prove the seam ({@code
+ * LoopHealthSource} reports what it is given) and nothing about what {@code Fleetd.main} actually
+ * gives it. This is the same hand-built-vs-config-wired shape as fleetd #561/#248/#426.
+ *
+ * <p>The fix extracts the inline {@code new} into {@link Fleetd#loopHealthSource}, a package-private
+ * factory in the same style as {@link Fleetd#capacitySource} and {@link Fleetd#healthCoverageSource}
+ * — which is exactly what makes it directly callable here. This test calls that factory with real
+ * {@link StatusPoller}/{@link SessionReaper} instances (never started, so no herdr or git I/O
+ * happens) and pins each half separately, plus the {@code reaper == null} branch: one invariant
+ * wired at three places needs three assertions, not one combined check whose non-zero total could
+ * hide a gap at any single place.
+ */
+class FleetdLoopHealthSourceWiringTest {
+
+    @Test
+    @DisplayName("the statusPoller half reports the real poller's health, not a hardcoded state")
+    void statusPollerHalfReflectsThePollersRealHealth() {
+        // Stopped without ever being started — stop() still marks the watchdog STOPPED. A poller
+        // that has never reported RUNNING is the discriminating case: if Fleetd.loopHealthSource
+        // ever hardcoded RUNNING (the exact mutation this test exists to catch), this would fail.
+        StatusPoller stoppedPoller = freshPoller();
+        stoppedPoller.stop();
+        SessionReaper unusedReaper = freshReaper(); // present only to satisfy the signature
+
+        FleetMcp.LoopHealthSource source = Fleetd.loopHealthSource(stoppedPoller, unusedReaper);
+
+        assertEquals(LoopWatchdog.State.STOPPED, source.statusPoller().get(),
+                "the statusPoller supplier must delegate to the real poller's health() — "
+                        + "replacing poller::health with a constant () -> RUNNING at the "
+                        + "Fleetd.loopHealthSource call site must fail this assertion");
+    }
+
+    @Test
+    @DisplayName("the sessionReaper half reports the real reaper's health, not a hardcoded state")
+    void sessionReaperHalfReflectsTheReapersRealHealth() {
+        StatusPoller unusedPoller = freshPoller(); // present only to satisfy the signature
+        SessionReaper stoppedReaper = freshReaper();
+        stoppedReaper.stop();
+
+        FleetMcp.LoopHealthSource source = Fleetd.loopHealthSource(unusedPoller, stoppedReaper);
+
+        assertEquals(LoopWatchdog.State.STOPPED, source.sessionReaper().get(),
+                "the sessionReaper supplier must delegate to the real reaper's health() — "
+                        + "replacing reaper.health() with a constant at the "
+                        + "Fleetd.loopHealthSource call site must fail this assertion");
+    }
+
+    @Test
+    @DisplayName("a null reaper (idle ttl not configured) still reports STOPPED, not a crash")
+    void nullReaperStillReportsStopped() {
+        // SessionReaper is only constructed when lifecycle.idleTtlSeconds is configured (see the
+        // `reaper` local in Fleetd.main) — a real deployment routinely passes null here. That null
+        // check is real behaviour, not a simplification to delete: it must keep reporting STOPPED
+        // rather than throwing a NullPointerException on the first fleet_list/healthz call.
+        StatusPoller runningPoller = freshPoller();
+
+        FleetMcp.LoopHealthSource source = Fleetd.loopHealthSource(runningPoller, null);
+
+        assertEquals(LoopWatchdog.State.STOPPED, source.sessionReaper().get(),
+                "reaper == null must still report STOPPED, exactly like an intentionally-stopped "
+                        + "reaper would — do not delete this null check to simplify the wiring");
+    }
+
+    /** Never started, so no herdr call is ever made; freshly constructed reports RUNNING. */
+    private static StatusPoller freshPoller() {
+        AgentControl agents = new AgentControl(new FakeHerdr());
+        return new StatusPoller(agents, new Injector(agents), 1000);
+    }
+
+    /** Never started, so no git/session I/O is ever made; freshly constructed reports RUNNING. */
+    private static SessionReaper freshReaper() {
+        return new SessionReaper(new SessionManager(new NeverSpawnsLauncher()), 60, 1000);
+    }
+
+    /**
+     * Same minimal shape as {@code FleetdBackendErrorSinkTest.NeverSpawnsLauncher} — every method
+     * throws or returns an empty/no-op value, since a {@link SessionReaper} that is only ever
+     * constructed and then stopped (never started) never calls any of them.
+     */
+    private static final class NeverSpawnsLauncher implements PeerLauncher {
+        @Override
+        public Set<Capability> capabilities() {
+            return Set.of();
+        }
+
+        @Override
+        public Set<Capability> capabilitiesFor(String profileName) {
+            return Set.of();
+        }
+
+        @Override
+        public PeerHandle spawn(SpawnRequest req) {
+            throw new UnsupportedOperationException("not reachable — this test never acquires a session");
+        }
+
+        @Override
+        public PeerHandle spawn(SpawnRequest req, PlacementDecision decision) {
+            throw new UnsupportedOperationException("not reachable — this test never acquires a session");
+        }
+
+        @Override
+        public Set<String> profiles() {
+            return Set.of();
+        }
+
+        @Override
+        public String defaultProfile() {
+            return null;
+        }
+
+        @Override
+        public String effectiveCwd(SpawnRequest req) {
+            throw new UnsupportedOperationException("not reachable — this test never acquires a session");
+        }
+
+        @Override
+        public List<String> parityOverlay(String profileName) {
+            return List.of();
+        }
+
+        @Override
+        public List<?> list() {
+            return List.of();
+        }
+
+        @Override
+        public int reapOrphanWorkers() {
+            return 0;
+        }
+
+        @Override
+        public void stop(String id) {
+        }
+
+        @Override
+        public boolean clearContext(String id) {
+            return false;
+        }
+    }
+}