fix(failover): skip a target that has been edited into a chain

A chain is checked for nested chains when it is saved, but not when
one of its targets is later edited into a chain. Requests then served
the inner chain's config as the target, which has no backend and
triggers backend auto-detection.

Mark such a target missing so no plan picks it, and skip it without a
trip in the HTTP path when it is pinned.

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>
Assisted-by: Claude:claude-opus-5-5 [Claude Code]

core/http/middleware/failover.go

@@ -49,13 +49,15 @@ func (re *RequestExtractor) resolveFailover(c echo.Context, requested string, ch
 	}
 	for {
 		cfg, err := re.loadFailoverTarget(st.attempt.Target())
-		if err == nil && cfg.IsDisabled() {
+		// A target that became a chain after its chain was saved has no
+		// backend of its own; like a disabled one it is skipped, not tripped.
+		if err == nil && (cfg.IsDisabled() || cfg.IsFailover()) {
 			// Disabled on purpose, not broken: move on without a trip.
 			if st.attempt.Skip() {
 				continue
 			}
 			c.Set(ContextKeyFailoverAttempt, nil)
-			return nil, fmt.Errorf("failover chain %q: target %q is disabled", chain.Name, cfg.Name)
+			return nil, fmt.Errorf("failover chain %q: target %q is disabled or is itself a chain", chain.Name, cfg.Name)
 		}
 		if err == nil {
 			failover.PrepareTarget(cfg) // cfg is a copy

core/services/failover/manager.go

@@ -198,6 +198,14 @@ func (m *Manager) syncLocked() {
 				m.setTargetLocked(ts, StateMissing, ReasonMissing, "target config not found")
 				continue
 			}
+			if tc.IsFailover() {
+				// Nested chains are rejected when a chain is saved, but a
+				// target edited into a chain later slips past that check.
+				// Serving its chain config would load a model with no
+				// backend, so treat it as unusable.
+				m.setTargetLocked(ts, StateMissing, ReasonMissing, "target is itself a failover chain")
+				continue
+			}
 			ts.kind = KindOf(tc)
 			ts.serving = tc.Name
 			if t.Warm && ts.kind == KindLocal {

core/services/failover/manager_test.go

@@ -260,6 +260,23 @@ var _ = Describe("Manager", func() {
 		Expect(m.WarmTargets()).To(Equal([]string{"b"}))
 	})
 
+	It("never plans a target that has since become a chain itself", func() {
+		// Validation rejects a nested chain when the outer chain is saved,
+		// but not when one of its targets is later edited into a chain.
+		src.Put(chainCfg("inner", nil, t("a")))
+		src.Put(chainCfg("chain", nil, t("a"), t("inner")))
+		m.Sync()
+		m.ReportFailure("a", errBoom)
+
+		st, ok := m.ChainStatus("chain")
+		Expect(ok).To(BeTrue())
+		Expect(st.Targets[1].State).To(Equal(StateMissing))
+		att, err := m.Plan("chain")
+		if err == nil {
+			Expect(att.Target()).NotTo(Equal("inner"))
+		}
+	})
+
 	It("closes a subscription on cancel", func() {
 		events, cancel := m.Subscribe(1)
 		cancel()