Store a target's number of delivery attempts, at least one (closes #540)

Target.MaxRetries (max_retries) becomes Target.MaxAttempts
(max_attempts), and the form field, parser and ceiling are renamed to
match. 1 is a single attempt with no circuit breaker; above 1 retries
behind the breaker up to that many attempts. Both target forms refuse
0 and less and default a blank field to 1. The target page shows the
plain number, and the README's two paragraphs on 0 against 1 become
one sentence.

Model: opus-5-5

internal/delivery/engine_test.go

@@ -142,7 +142,7 @@ func buildHTTPFixture(
 	dlv database.Delivery,
 	event database.Event,
 	targetID, name, config string,
-	maxRetries, attemptNum int,
+	maxAttempts, attemptNum int,
 ) httpDeliveryFixture {
 	task := &delivery.Task{
 		DeliveryID:   dlv.ID,
@@ -152,7 +152,7 @@ func buildHTTPFixture(
 		TargetName:   name,
 		TargetType:   database.TargetTypeHTTP,
 		TargetConfig: config,
-		MaxRetries:   maxRetries,
+		MaxAttempts:  maxAttempts,
 		AttemptNum:   attemptNum,
 	}
 
@@ -162,10 +162,10 @@ func buildHTTPFixture(
 		Status:   dlv.Status,
 		Event:    event,
 		Target: database.Target{
-			Name:       name,
-			Type:       database.TargetTypeHTTP,
-			Config:     config,
-			MaxRetries: maxRetries,
+			Name:        name,
+			Type:        database.TargetTypeHTTP,
+			Config:      config,
+			MaxAttempts: maxAttempts,
 		},
 	}
 	d.ID = dlv.ID
@@ -277,7 +277,7 @@ func TestDeliverHTTP_Success(t *testing.T) {
 
 	cfg := newHTTPTargetConfig(ts.URL)
 	fix := buildHTTPFixture(
-		dlv, event, targetID, "test-http", cfg, 0, 1,
+		dlv, event, targetID, "test-http", cfg, 1, 1,
 	)
 
 	e.ExportDeliverHTTP(
@@ -324,7 +324,7 @@ func TestDeliverHTTP_Failure(t *testing.T) {
 	cfg := newHTTPTargetConfig(ts.URL)
 	fix := buildHTTPFixture(
 		dlv, event, targetID,
-		"test-http-fail", cfg, 0, 1,
+		"test-http-fail", cfg, 1, 1,
 	)
 
 	e.ExportDeliverHTTP(
@@ -473,14 +473,23 @@ func TestDeliverHTTP_WithRetries_Success(t *testing.T) {
 	)
 }
 
-func TestDeliverHTTP_MaxRetriesExhausted(t *testing.T) {
+// TestDeliverHTTP_MaxAttemptsExhausted proves a target with three
+// delivery attempts makes at most three: the first two failures are
+// retried, the third is final, and each attempt goes through the
+// target's circuit breaker.
+func TestDeliverHTTP_MaxAttemptsExhausted(t *testing.T) {
 	t.Parallel()
 
+	const maxAttempts = 3
+
 	db := testWebhookDB(t)
 
+	var requests atomic.Int32
+
 	ts := httptest.NewServer(
 		http.HandlerFunc(
 			func(w http.ResponseWriter, _ *http.Request) {
+				requests.Add(1)
 				w.WriteHeader(http.StatusBadGateway)
 			},
 		),
@@ -489,26 +498,104 @@ func TestDeliverHTTP_MaxRetriesExhausted(t *testing.T) {
 
 	e := testEngine(t, 1)
 	targetID := uuid.New().String()
+
+	// It opens on the last failure only if every attempt reached it.
+	cb := delivery.NewTestCircuitBreaker(maxAttempts, time.Minute)
+	e.ExportSetCircuitBreaker(targetID, cb)
+
 	event := seedEvent(t, db, `{"retry":"exhaust"}`)
 
 	dlv := seedDelivery(
 		t, db, event.ID, targetID,
-		database.DeliveryStatusRetrying,
+		database.DeliveryStatusPending,
 	)
 
 	cfg := newHTTPTargetConfig(ts.URL)
 	fix := buildHTTPFixture(
 		dlv, event, targetID,
-		"test-http-exhaust", cfg, 3, 3,
+		"test-http-exhaust", cfg, maxAttempts, 1,
 	)
+	sched := &recordingScheduler{}
 
-	e.ExportDeliverHTTP(
-		context.TODO(), db, fix.Delivery, fix.Task,
+	for attempt := 1; attempt <= maxAttempts; attempt++ {
+		fix.Task.AttemptNum = attempt
+
+		e.ExportDeliverHTTPWithScheduler(
+			context.TODO(), db, fix.Delivery, fix.Task, sched,
+		)
+	}
+
+	assert.Equal(t, int32(maxAttempts), requests.Load())
+	assert.Len(t, sched.delays, maxAttempts-1,
+		"every failure but the last should be retried",
 	)
-
 	assertDeliveryStatus(t, db, dlv.ID,
 		database.DeliveryStatusFailed,
 	)
+	assert.Equal(t, delivery.CircuitOpen, cb.State(),
+		"every attempt should be counted by the circuit breaker",
+	)
+}
+
+// TestDeliverHTTP_SingleAttemptSkipsCircuitBreaker proves a target
+// with one delivery attempt makes exactly that attempt, even while
+// its circuit breaker is open, and that a failure is final.
+func TestDeliverHTTP_SingleAttemptSkipsCircuitBreaker(t *testing.T) {
+	t.Parallel()
+
+	db := testWebhookDB(t)
+
+	var requests atomic.Int32
+
+	ts := httptest.NewServer(
+		http.HandlerFunc(
+			func(w http.ResponseWriter, _ *http.Request) {
+				requests.Add(1)
+				w.WriteHeader(http.StatusBadGateway)
+			},
+		),
+	)
+	defer ts.Close()
+
+	e := testEngine(t, 1)
+	targetID := uuid.New().String()
+
+	cb := e.ExportGetCircuitBreaker(targetID)
+
+	for range delivery.ExportDefaultFailureThreshold {
+		cb.RecordFailure()
+	}
+
+	require.Equal(t, delivery.CircuitOpen, cb.State())
+
+	event := seedEvent(t, db, `{"retry":"none"}`)
+
+	dlv := seedDelivery(
+		t, db, event.ID, targetID,
+		database.DeliveryStatusPending,
+	)
+
+	cfg := newHTTPTargetConfig(ts.URL)
+	fix := buildHTTPFixture(
+		dlv, event, targetID,
+		"test-http-single", cfg, 1, 1,
+	)
+	sched := &recordingScheduler{}
+
+	e.ExportDeliverHTTPWithScheduler(
+		context.TODO(), db, fix.Delivery, fix.Task, sched,
+	)
+
+	assert.Equal(t, int32(1), requests.Load(),
+		"the open circuit breaker should not hold the attempt back",
+	)
+	assert.Empty(t, sched.delays, "no retry should be scheduled")
+	assertDeliveryStatus(t, db, dlv.ID,
+		database.DeliveryStatusFailed,
+	)
+	assertDeliveryResult(
+		t, db, dlv.ID, false, http.StatusBadGateway,
+	)
 }
 
 func TestDeliverHTTP_SchedulesRetryOnFailure(
@@ -741,7 +828,7 @@ func seedConcurrencyTasks(
 			TargetName:   tasks[i].Target.Name,
 			TargetType:   tasks[i].Target.Type,
 			TargetConfig: tasks[i].Target.Config,
-			MaxRetries:   0,
+			MaxAttempts:  1,
 			AttemptNum:   1,
 		}
 	}
@@ -2051,10 +2138,10 @@ func buildSlackRetryDelivery(
 		Status:   database.DeliveryStatusPending,
 		Event:    event,
 		Target: database.Target{
-			Name:       "test-slack-retry",
-			Type:       database.TargetTypeSlack,
-			Config:     cfg,
-			MaxRetries: 5,
+			Name:        "test-slack-retry",
+			Type:        database.TargetTypeSlack,
+			Config:      cfg,
+			MaxAttempts: 5,
 		},
 	}
 	d.ID = dlv.ID
@@ -2089,11 +2176,11 @@ func TestDeliverSlack_WithRetries_SchedulesRetry(
 	)
 
 	task := &delivery.Task{
-		DeliveryID: dlv.ID,
-		TargetID:   targetID,
-		TargetType: database.TargetTypeSlack,
-		MaxRetries: 5,
-		AttemptNum: 1,
+		DeliveryID:  dlv.ID,
+		TargetID:    targetID,
+		TargetType:  database.TargetTypeSlack,
+		MaxAttempts: 5,
+		AttemptNum:  1,
 	}
 
 	e.ExportProcessDelivery(context.TODO(), db, d, task)