fix(failover): preserve manual bench against automatic cooldown downgrade

recordTransientFailure and benchNow unconditionally set manual=false and
reset until to now+cooldown. When the best-effort all-benched failover path
re-tries a model an operator manually benched via BenchModel, a subsequent
failure downgraded manual=true -> false and could shorten the operator's
window to the short auto cooldown.

Both functions now read existing state: if it is an active manual bench
(manual && now.Before(until)) they bump consecutiveFails but keep manual=true
and the later until. Non-manual or expired-manual state still gets the
automatic cooldown. Adds TestFailover_ManualBenchSurvivesAutomaticDowngrade
covering no-prior, prior-auto, active-manual, and expired-manual cases.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

v2/failover_test.go

@@ -300,3 +300,82 @@ func TestNewFailoverModel_Flattens(t *testing.T) {
 		}
 	}
 }
+
+// TestFailover_ManualBenchSurvivesAutomaticDowngrade is a regression test:
+// an active manual bench (long window) must NOT be cleared or shortened by the
+// automatic recordTransientFailure/benchNow paths. The best-effort all-benched
+// failover loop can re-try a manually benched model; if it fails, the automatic
+// logic previously overwrote manual=true -> false and shortened until to the
+// short auto cooldown. The operator's intent must win.
+func TestFailover_ManualBenchSurvivesAutomaticDowngrade(t *testing.T) {
+	resetHealthForTest()
+
+	const key = "p/manual"
+	longUntil := time.Now().Add(time.Hour)
+	shortCooldown := time.Minute
+	now := time.Now()
+
+	// Operator manually benches the model for a long window.
+	BenchModel(key, longUntil)
+
+	assertManualPreserved := func(stage string) {
+		t.Helper()
+		list := ListBenched()
+		var got *BenchedModel
+		for i := range list {
+			if list[i].Model == key {
+				got = &list[i]
+				break
+			}
+		}
+		if got == nil {
+			t.Fatalf("%s: %q missing from ListBenched; manual bench was cleared", stage, key)
+		}
+		if !got.Manual {
+			t.Errorf("%s: Manual=false, want true (automatic logic downgraded manual bench)", stage)
+		}
+		if !got.Until.Equal(longUntil) {
+			t.Errorf("%s: Until=%v, want %v (automatic logic shortened operator window)", stage, got.Until, longUntil)
+		}
+	}
+
+	// (c) Active manual bench hit by the automatic transient path.
+	benched, until := globalHealth.recordTransientFailure(key, shortCooldown, now)
+	if !benched {
+		t.Errorf("recordTransientFailure: benched=false, want true (model stays benched)")
+	}
+	if !until.Equal(longUntil) {
+		t.Errorf("recordTransientFailure: until=%v, want %v (long manual window preserved)", until, longUntil)
+	}
+	assertManualPreserved("after recordTransientFailure")
+
+	// (c) Active manual bench hit by the automatic auth-dead path.
+	until = globalHealth.benchNow(key, shortCooldown, now)
+	if !until.Equal(longUntil) {
+		t.Errorf("benchNow: until=%v, want %v (long manual window preserved)", until, longUntil)
+	}
+	assertManualPreserved("after benchNow")
+
+	// (d) Expired manual bench: automatic logic IS allowed to take over.
+	resetHealthForTest()
+	expired := time.Now().Add(-time.Hour)
+	BenchModel(key, expired)
+	until = globalHealth.benchNow(key, shortCooldown, now)
+	if want := now.Add(shortCooldown); !until.Equal(want) {
+		t.Errorf("benchNow on expired manual: until=%v, want auto cooldown %v", until, want)
+	}
+
+	// (a) No prior state and (b) prior automatic bench: automatic cooldown applies.
+	resetHealthForTest()
+	benched, until = globalHealth.recordTransientFailure(key, shortCooldown, now) // (a)
+	if !benched || !until.Equal(now.Add(shortCooldown)) {
+		t.Errorf("recordTransientFailure(no prior): benched=%v until=%v, want true %v", benched, until, now.Add(shortCooldown))
+	}
+	until = globalHealth.benchNow(key, shortCooldown, now) // (b) prior automatic state
+	if want := now.Add(shortCooldown); !until.Equal(want) {
+		t.Errorf("benchNow(prior auto): until=%v, want %v", until, want)
+	}
+	if list := ListBenched(); len(list) != 1 || list[0].Manual {
+		t.Errorf("automatic bench should not be Manual: %+v", list)
+	}
+}